Search

The use of implantable biomaterials, such as artificial skin substitutes used for dermal defects, remains limited by the low angiogenic potential of these products. The rapid in vivo degradation of growth factors contributes to the limiting of angiogenesis in biomaterials. Here, we report on collagen sponges in which vascular endothelial growth factor (VEGF) was immobilized through physical binding to heparin, covalently incorporated in the matrix via cross-linking with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide. The in vitro release of VEGF over time and endothelial cell proliferation were investigated in matrices modified at varying heparin to EDC ratios either nonloaded or loaded with VEGF. ELISA demonstrated a significantly slower in vitro release of VEGF over a period of 5 days from heparinized matrices as compared to their unmodified and cross-linked counterparts. The effects of these modifications on the proliferation of endothelial cells and endothelial progenitor cells were evaluated after 1, 3 and 5 days either according to the bromodeoxyuridine assay or total cell counting with a Neubauer chamber. The endothelial and endothelial progenitor cells cultured in contact with heparinized matrices loaded with VEGF revealed both the highest rate of DNA synthesis and the highest total cell count. Furthermore, these results show that the cross-linking of collagen matrices – both in the presence and absence of heparin – leads to increases of the proliferative activities. We can assume that these changes lead to matrices with increased angiogenic capabilities.

The poor vascularization rate of matrices following cell invasion is considered to be one of the main shortcomings of scaffolds used in tissue engineering. In the past decade much effort has been directed towards enhancing the angiogenic potential of biomaterials. A great many studies have appeared reporting about enhancement of vascularization by immobilizing angiogenic factors, such as vascular endothelial growth factor (VEGF) and basic fibroblast growth factor-2 (FGF-2). We have also tried to achieve this goal by modifying collagen matrices by covalent incorporation of heparin into the matrices and loading them with VEGF. We and others have observed that loading angiogenic factors to heparinized materials markedly increases angiogenic capacity. In the present paper we also investigated the angiogenic properties of collagen matrices which were only cross-linked, i.e. in the absence of heparin. The angiogenic capacity of the modified matrices was evaluated using the chorioallantoic membrane assay. Differences in angiogenic potential were deduced from macroscopic and microscopic analyses of the chorioallantoic membrane, as well as from dry weight changes. Cross-linked only matrices and matrices both cross-linked and heparinized appeared to show a significantly larger angiogenic potential than unmodified matrices. As previously observed, loading VEGF to these matrices further stepped up angiogenic potential. Quite surprisingly, cross-linking had a substantial impact on angiogenic potential. In terms of magnitude, this effect was similar to the effect of loading VEGF to heparinized matrices. Both modification procedures resulted in an increase of average pore size within the collagen matrices, and this observation may explain the more rapid invasion of mouse fibroblasts into cross-linked and heparinized matrices. Form changes of the implants were also monitored during the in vivo contacts: cross-linked and heparinized matrices showed far better resistance against contraction, as compared to unmodified matrices. Results from the chorioallantoic membrane assay experiments were compared with data obtained from rat model experiments, which confirmed the results from the chorioallantoic membrane assay. This relatively simple assay was again shown to be extremely helpful in evaluating and predicting the angiogenic capabilities of biomaterials for use in tissue engineering and wound healing.

Since the survival of ingrowing cells in biomaterials for regenerative processes largely depends on the supply of nutrients and oxygen, angiogenesis plays an important role in the development of new materials for tissue engineering. In this study we investigated the possibility of enhancing the angiogenic properties of collagen matrices by covalent incorporation of the vascular endothelial growth factor (VEGF). In a previous paper we already reported the use of homo- and heterobifunctional cross-linking agents for modifying collagen matrices [1]. In the present work the angiogenic growth factor was linked to the collagen with the homobifunctional cross-linker disuccinimidyldisuccinatepolyethyleneglycol (SS-PEG-SS) in a two step procedure. The efficiency of the first reaction step-the reaction of SS-PEG-SS with VEGF--was evaluated by western blot analysis. After 10 minutes virtually all of the dimeric molecules VEGF were on average modified by conjugation with 1 cross-linking molecule. The biological activity of the conjugate was investigated by exposing endothelial cells to non-modified VEGF and to VEGF conjugated to the cross-linker. The conjugation only had a limited effect on the mitogenic activity of VEGF. We therefore applied the cross-linking reaction to the VEGF-collagen system. In a first approach the changes were evaluated by the in vitro exposure of HUVECs to non-modified matrices, to matrices in which the VEGF was simply admixed and to matrices in which the VEGF was covalently incorporated. The angiogenic properties were evaluated in vivo with the chorioallantois membrane model. In this assay the chorioallantois membrane of the chicken embryo was exposed to the same set of matrices. The covalent incorporation of VEGF has a small but significant effect both on the formation of microvessels in the chorioallantois membrane and the tissue ingrowth into the implant. The covalent incorporation of angiogenic growth factors may thus be considered as a promising approach for enhancing the angiogenic capabilities of collagen matrices. Also the cross-linking with the homobifunctional cross-linking agent has a positive effect on the angiogenic potential of the collagen matrices.

One of the prominent shortcomings of matrices for tissue engineering is their poor ability to support angiogenesis. We report here on experiments to enhance the angiogenic properties of collagen matrices. Our aim is to achieve this goal by covalently incorporating heparin into collagen matrices and by physically immobilizing angiogenic vascular endothelial growth factor (VEGF) to the heparin. The immobilization of heparin was performed with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) and N-hydroxysuccinimide (NHS). Carboxyl groups on the heparin are activated to succinimidyl esters, which react with amino functions on the collagen to zero length cross-links. This modification leads--in addition to the incorporation of heparin--to gross changes in in vitro degradation behavior and water-binding capacity. As a first approach to testing angiogenic capabilities, endothelial cells were exposed to nonmodified and heparinized collagen matrices. This exposure leads to an increase in endothelial cell proliferation. The increase can be further enhanced by loading the (heparinized) collagen matrices with VEGF. Evaluation of the angiogenic potential of heparinized matrices was further investigated by exposing them to the chorioallantoic membrane of chicken embryos and to the subcutaneous tissue of rats. Both approaches show that heparinized matrices have substantially increased angiogenic potential. In particular, the loading of heparinized matrices with VEGF invokes a further increase in angiogenic potential. It is apparent that the physical binding of VEGF to heparin allows for a release that is beneficial to angiogenesis. By varying the heparin and EDC/NHS concentrations during the modification process and by varying the loading with VEGF, the angiogenic potential as well as the degradation behavior can be adapted to obtain matrices that fulfill specific angiogenic requirements in the field of tissue engineering.

A novel technique is used to produce an open porous titanium dioxide/glass composite, named Ecopore, with promising structural and biological properties for the development as a bone graft. This study aims at a fast and lasting integration of the new material by means of biochemical surface modification. Surface etching of Ecopore, aminosilanization and covalent coupling of the cellular attachment mediator fibronectin was employed as modification strategy. In a comparison of different etching procedures, alkaline etching led to the highest density of amino functions after subsequent aminosilanization. Fibronectin was immobilized using a bifunctional aminoreactive PEG-linker. This protein coating improved the attachment of human osteoblast-like cells (HOB) on non-porous Ecopore as displayed by vital staining. XTT metabolism assays indicated an enhanced HOB growth in the initial phase of cultivation on fibronectin-coated versus non-coated specimens. In a first feasibility study, cultivation of HOB on coated porous Ecopore cylinders with a median pore size diameter of 130μm showed that cellular growth was uniform and dense on the external surface of the specimen, but was sparse in the interior pore system. Ecopore batches with larger pores will be modified and investigated in vitro and in vivo in the next step of the study.

The realization of three-dimensional (3D) degradable matrices which slowly release bio-active components represents a major challenge in the field of tissue engineering. In this paper we report on the usage of commercially available bifunctional agents for both the covalent coupling of proteins to and the cross-linking of collagen matrices. Proteins – horse radish peroxidase (HRP) was used as a model protein – were cross-linked with either a homobifunctional (disuccinimidyldisuccinatepolyethylene-glycol) or a heterobifunctional (N-hydroxysuccinimidylvinylsulfonepolyethyleneglycol) agent. In the case of the heterobifunctional cross-linking agent the collagen matrices were previously modified with succinimidylacetylthioacetate in order to introduce sulfhydryl groups. As compared with control experiments a 10-fold and 50-fold increase of immobilized proteins were achieved with the homobifunctional and heterobifunctional cross-linker resp. The HRP–PEG conjugates demonstrated a better long-term stability as compared to the non-treated HRP. The effects of the cross-linking agents and the thiolation reagent succinimidylacetylthio acetate on the in vitro degradation of the collagen matrices by collagenase were also investigated. In particular the reaction with succinimidylacetylthio acetate appears to offer interesting opportunities both for coupling active proteins and modulating the degradation times of collagen matrices.

The application of collagen matrices in covering wound defects has been under investigation for quite some time. First applications led to the development of Integra®, a well-known product consisting of collagen and chondroitin sulfate cross-linked with glutaraldehyde and contained on a silicon foil. Application of this product requires a two-stage procedure necessitating hospitalisation of the recipient for about 2 weeks. Subsequent to vascularisation of the collagen, the foil is removed and the collagen surface is covered with autologous split skin in the second stage. The long hospitalisation period creates a need for a material of improved angiogenic capabilities.

This study aimed to analyze the role of endothelial progenitor cell (EPC)-derived angiogenic factors and chemokines in the multistep process driving angiogenesis with a focus on the recently discovered macrophage migration inhibitory factor (MIF)/chemokine receptor axis. Primary murine and murine embryonic EPCs (eEPCs) were analyzed for the expression of angiogenic/chemokines and components of the MIF/CXC chemokine receptor axis, focusing on the influence of hypoxic versus normoxic stimulation. Hypoxia induced an upregulation of CXCR2 and CXCR4 but not CD74 on EPCs and triggered the secretion of CXCL12, CXCL1, MIF, and vascular endothelial growth factor (VEGF). These factors stimulated the transmigration activity and adhesive capacity of EPCs, with MIF and VEGF exhibiting the strongest effects under hypoxia. MIF-, VEGF-, CXCL12-, and CXCL1-stimulated EPCs enhanced tube formation, with MIF and VEGF exhibiting again the strongest effect following hypoxia. Tube formation following in vivo implantation utilizing angiogenic factor-loaded Matrigel plugs was only promoted by VEGF. Coloading of plugs with eEPCs led to enhanced tube formation only by CXCL12, whereas MIF was the only factor which induced differentiation towards an endothelial and smooth muscle cell (SMC) phenotype, indicating an angiogenic and differentiation capacity in vivo. Surprisingly, CXCL12, a chemoattractant for smooth muscle progenitor cells, inhibited SMC differentiation. We have identified a role for EPC-derived proangiogenic MIF, VEGF and MIF receptors in EPC recruitment following hypoxia, EPC differentiation and subsequent tube and vessel formation, whereas CXCL12, a mediator of early EPC recruitment, does not contribute to the remodeling process. By discerning the contributions of key angiogenic chemokines and EPCs, these findings offer valuable mechanistic insight into mouse models of angiogenesis and help to define the intricate interplay between EPC-derived angiogenic cargo factors, EPCs, and the angiogenic target tissue.

The early observation of extra copper in preparations of cytochrome-c oxidase has recently lead to a renewed interest in its stoichiometry and possible redox function. In various, pure preparations (heme A contents close to the theoretical value of 9.79 nmol/mg protein for the 13-subunit bovine enzyme) protein-related metal stoichiometries of 3 Cu, 2 Fe, 1 Zn, 1 Mg/monomer with Mr 204266 were determined. Despite the presence of five potential redox metal ions, reductive and reoxidative titrations indicate the presence of only four one-electron-accepting/donating species in the ligand-free enzyme. Participation of two copper ions in a binuclear copper site acting as a one-electron acceptor may explain both the observed copper stoichiometry and the redox behaviour. The homology of the C-terminal sequence of subunit II with one of the copper-binding sites in nitrous-oxide reductases provides possible ligands for complexing two copper ions in a binuclear center.

Two methods are described for the purification of cytochrome c oxidase from Triton X-100 extracts of the periplasma membrane of Paracoccus denitrificans . The first is a large-scale procedure for the preparation of 100–250 nmol of cytochrome c oxidase (10–20 mg) in 1 week. The second is a rapid procedure for isolating up to 25 nmol in 2–3 days. Owing to the high yields given by fast protein liquid chromatography (FPLC) on Mono Q columns, the overall yield is about 20%, whereas the yield in many other previously published procedures does not exceed 10%. The use of FPLC on Mono Q also offers a considerable saving of time.

The most commonly used biomaterials fail to ensure sufficient angiogenesis for fast in vivo incorporation. This results in central necrosis and consequent infection. One way of obtaining a high angiogenic response is the application of vascular endothelial growth factor (VEGF). To obtain a sustained release of these cytokines, heparin was incorporated into collagen matrices using 1-ethyl-3(3-dimethyl-aminopropyl) carbodiimide (EDC) and N-hydroxysuccinmide (NHS). The functionality of the heparinized collagen matrices was then enhanced by immobilization of VEGF via its heparin-binding domain. This procedure changed in vitro degradation behavior and water-binding capacity. Accelerated endothelial cell proliferation was also achieved. A range of different heparin and EDC/NHS concentrations in combination with VEGF induced variation in endothelial cell growth and tubulogenic formation. Polymerized collagen scaffolds presented biointeractive systems with integrated angiogenic activity. This may become a useful tool in the clinical therapy of disorders connected with wound healing.

The in vivo application of engineered matrices in human wound healing processes is often hampered by the slow rate of vascularization. Therefore much research is directed towards enhancing the angiogenic properties of such matrices. One approach for enhancing the vascularization is the incorporation of angiogenic growth factors. Recently, we and others have reported on immobilizing such factors into collagen matrices either by covalent attachment or by physical binding to covalently incorporated heparin. Especially the latter procedure has been shown to lead to substantial increase rates in vascularization in in vivo experiments. The increases have been proposed to depend on the sustained release of the incorporated angiogenic growth factors from the heparinized collagen matrices. In this paper, we report on investigations to study the release of vascular endothelial growth factor (VEGF) from collagen matrices under conditions which mimic potential in vivo situations. Relevant proteinase concentrations were deduced from in vitro experiments in which we evaluated the secretion of selected matrix metalloproteinases from fibroblasts in contact with collagen. The release of VEGF from non-modified, cross-linked and heparinized collagen matrices in the absence and in the presence of varying concentrations of proteinases was then determined by ELISA and liquid scintillation counting. The release behaviour appears to be controlled by both the presence of heparin and the levels of proteinases applied. Experiments with matrices containing radioactively labelled heparin suggest that VEGF release results from the consecutive and simultaneous release of three species of VEGF molecules that differ in their binding affinities to the differently modified collagen matrices. The species binding specifically to heparin most likely accounts for the previously observed increases in angiogenic potential between loading VEGF to non-heparinized and heparinized collagen matrices.

The vascularization of engineered tissues in many cases does not keep up with the ingrowth of cells. Nutrient and oxygen supply are not sufficient, which ultimately leads to the death of the invading cells. The enhancement of the angiogenic capabilities of engineered tissues therefore represents a major challenge in the field of tissue engineering. The immobilization of angiogenic growth factors may be useful for enhancing angiogenesis. The most potent angiogenic growth factor specific to endothelial cells, vascular endothelial growth factor (VEGF), occurs in several splice variants. The variant with 165 amino acids both has a high angiogenic activity and a high affinity for heparin. We therefore incorporated heparin molecules into collagen matrices by covalently cross-linking them to amino functions on the collagen. Physical binding of VEGF to the heparin may then prevent a rapid clearance from the implant, while the release rate may become coupled to the degradation of the collagen matrix. The modified matrices were characterized by determination of the extent of the heparin immobilization, the in vitro degradation rate by collagenase. For testing the angiogenic properties, non-modified and heparinized collagen specimens were – either loaded with VEGF or non-loaded – subcutaneously implanted on the back of rats. Specimens were explanted after varying periods of implantation, the dry weights and the hemoglobin contents, as well as immunostained histological sections were evaluated: heparinized collagen matrices loaded with VEGF are vascularized to a substantially higher extent as compared to non-modified matrices.

Soft tissue defects represent a challenge in plastic surgery. Therefore many research efforts have focused onto materials that support tissue formation and especially angiogenesis. But still most of the commercially available products can serve only as temporary coverage due to the small angiogenic potency.

In this study, we introduce a porous composite material, termed "Ecopore", and describe in vitro investigation of the material and its modification with fibronectin. The material is a sintered compound of rutile TiO2 and the volcanic silicate perlite with a macrostructure of interconnecting pores. It is both inexpensive and easy to manufacture. We first investigated Ecopore for corrosion and leaching of elements in physiological saline. The corrosion supernatants did not contain critical concentrations of toxic trace elements. In an in vitro model, human primary osteoblasts (HOB) were cultured directly on Ecopore. HOB grew on the composite as well as on samples of its single constituents, TiO2 and perlite glass, and remained vital, but cellular spreading was less than on tissue culture plastic. The pro-inflammatory cytokines IL-1 and TNF-alpha were below detection limits in HOB culture supernatants, whereas IL-6 was detectable on a low level. To enhance cellular attachment and growth, the surface of the composite was modified by etching, functionalization with aminosilane and coupling of fibronectin. This modification greatly enhanced the spreading of HOB, indicated by vital staining and Sodium 3'-[1-(phenylaminocarbonyl)-3,4-tetrazolium]-bis (4-methoxy-6-nitro) benzene sulfonic acid hydrate (XTT) metabolism assays. HOB grew on the entire visible surface of porous fibronectin-modified composite, expressing alkaline phosphatase, a mature osteoblast marker. We conclude that Ecopore is non-toxic and sustains HOB growth, cellular spreading being improvable by coating with fibronectin. The composite may be usable in the field of bone substitution.

Multifrequency electron paramagnetic resonance (EPR) spectra of the Cu(II) site in bovine heart cytochrome c oxidase (COX) and nitrous oxide reductase (N2OR) from Pseudomonas stutzeri confirm the existence of Cu-Cu interaction in both enzymes. C-band (4.5 GHz) proves to be a particularly good frequency complementing the spectra of COX and N2OR recorded at 2.4 and 3.5 GHz. Both the high and low field region of the EPR spectra show the presence of a well-resolved 7-line pattern consistent with the idea of a binuclear Cu center in COX and N2OR. Based on this assumption consistent g-values are calculated for gz and gx at four frequencies. No consistent g-values are obtained with the assumption of a 4-line pattern indicative for a mononuclear Cu site.

The multicopper proteins, nitrous-oxide reductase (N2OR) and cytochrome c oxidase (COX), were investigated by EPR spectroscopy at microwave frequencies 2.4-35 GHz. Our results support a Cu-Cu interaction in COX and N2OR. At least 10 lines in the 2.7-GHz, 12 lines in the 4.6-GHz and 14 lines in the 9.2 GHz spectra were resolved for N2OR. Eight copper lines at 2.7 GHz, about nine lines at 4.6 GHz and about six lines at 9.2 GHz were resolved for COX. Simulations of the EPR spectra were consistent with most of the resonances of the multiline spectra, including regions in the center of the spectra where overlap of the three seven-line patterns is proposed. These simulations indicated that Cu-Cu interaction, in a mixed-valence [Cu(1.5) ... Cu(1.5)], S = 1/2 site is consistent with, if not proof of, the unusual spectral features observed for N2OR and COX.

Preparations and protein chemical characterizations performed with cytochrome c oxidase (E.C. 1.9.3.1) from the purple bacterium Paracoccus denitrificans are reviewed. The simplest catalytically competent complex of the enzyme consists of two subunits of 62012 and 2799 Da. The theoretical heme a/protein ratio of the purified enzyme is 22.0 nmol/mg. The amino acid sequences of both proteins are compared with examples of subunits I and II of mitochondrial terminal oxidases from the main kingdoms of eukaryotes. The significance of the emerging conserved features such as membrane penetration patterns, invariant residues, stoichiometry, and sites of prosthetic groups are discussed. The Paracoccus enzyme represents the only prokaryotic oxidase detailed so far, which is directly related to the mitochondrial oxidases by common ancestry in the growing O2 atmosphere.

Metal contents of preparations of procaryotic (Paracoccus denitrificans) and eucaryotic (beef heart) cytochrome c oxidases have been determined by inductively coupled plasma atomic emission spectroscopy and shown to be stoichiometrically related to the protein contents. The results show that oxidases which possess subunits I and II have three copper atoms besides hemes a and a3 (Paracoccus denitrificans, Cu: 2.97 +/- 0.08 and Fe: 2.09 +/- 0.10; bovine heart, Cu: 2.83 +/- 0.07 and Fe: 1.94 +/- 0.12). Together with data reported for the c1 aa3 oxidase from Thermus thermophilus, the following conclusions can be drawn. Subunit I binds two copper atoms and both hemes a and a3 and thus is the universal terminal oxidase of this spectral type. Subunit II binds one copper and functions as an electron conductor. The mitochondrial respiratory complex IV binds, in addition to three copper and two hemes a, stoichiometric amounts of magnesium and zinc (bovine heart Mg: 0.98 +/- 0.05 and Zn: 1.01 +/- 0.04).

Cytochrome c oxidase (EC 1.9.3.1) is the terminal enzyme of the mitochondria respiratory chain catalysing electron transfer from cytochrome c to molecular oxygen [ 1,2]. The molecular mechanism of this process is still not understood. At present, little is known about such important structural features as the position of the prosthetic groups or the location and characteristics of the cytochrome c binding sites in the cytochrome c oxidase complex 131. The aim of this paper is to provide information about this latter problem as part of a more general effort of our laboratories to elucidate the relationship between structure and functions of cytochrome c oxidase. as in [S]. Cytochrome c oxidase was isolated from beef heart as in [7], the final dialysis step was omitted. The activity, measured polarographically in 0.5% Tween 80, 50 mM phosphate buffer (pH_7i4) ranged_fym 130170 mol cytochrome c. s . molaa3 . The covalent enzyme-substrate complex was

Recent structure determinations suggested a new binding site for a non-redox active metal ion in subunit I of cytochrome c oxidase both of mitochondrial and of bacterial origin. We analyzed the relevant metal composition of the bovine and the Paracoccus denitrificans enzyme and of bacterial site-directed mutants in several residues presumably liganding this ion. Unlike the mitochondrial enzyme where a low, substoichiometric content of Ca2+ was found, the bacterial wild-type (WT) oxidase showed a stoichiometry of one Ca per enzyme monomer. Mutants in Asp-477 (in immediate vicinity of this site) were clearly diminished in their Ca content and the isolated mutant enzyme revealed a spectral shift in the heme a visible absorption upon Ca addition, which was reversed by Na ions. This spectral behavior, largely comparable to that of the mitochondrial enzyme, was not observed for the bacterial WT oxidase. Further structure refinement revealed a tightly bound water molecule as an additional Ca2+ ligand.

Dicyclohexylcarbodiimide (DCCD) reacted with beef heart cytochrome c oxidase to inhibit the proton-pumping function of this enzyme and to a lesser extent to inhibit electron transfer. The modification of cytochrome c oxidase in detergent dispersion or in vesicular membranes was in subunits II–IV. Labelling followed by fragmentation studies showed that there is one major site of modification in subunit III. DCCD was also incorporated into several sites in subunit II and at least one site in subunit IV. The major site in subunit III has a specificity for DCCD at least one order of magnitude greater than that of other sites (in subunits II and IV). Its modification could account for all of the observed effects of the reagent, at least for low concentrations of DCCD. Labelling of subunit II by DCCD was blocked by prior covalent attachment of arylazidocytochrome c, a cytochrome c derivative which binds to the high-affinity binding site for the substrate. The major site of DCCD binding in subunit III was sequenced. The label was found in glutamic acid 90 which is in a sequence of eight amino acids remarkably similar to the DCCD-binding site within the proteolipid protein of the mitochondrial ATP synthetase.

Bioenergetic processes as photosynthesis and respiration occupy pride of place in biochemistry as well from their reaction quantity and their meaning for the maintainance of life as from the interest biochemists have focussed on them. From a proteinchemist standpoint, however, analytical progress in this field has come up only slowly if at all. The reason for this is that the main reactions of energy conversion are catalyzed by multisubunit membrane enzymes, the attempts at isolation, purification, crystallization and proteinchemical characterization of which being futile if they follow the rules of common biochemical methodology. Thus none of the eucaryotic photosynthetic or respiratory enzyme complexes has been completely described by proteinchemical methods nor has a 3d crystallization suitable for x-ray analysis been achieved. In the following we focus the problem of obtaining and evidencing integrity with one of the proteinchemically better characterized enzymes, the terminal complex IV of the mitochondrial respiratory chain, cytochrome c oxidase (EC.1.9.3.1) which we have analyzed in recent years.

Polypeptide VII of cytochrome c oxidase was isolated and purified by gel filtration on Bio-Gel P-10 in 10% acetic acid. Automatic Edman degradation of this peptide chain was not successful, because it is blocked at the N-terminus. The amino acid analysis shows a relatively high content of hydrophilic residues (54%). On the basis of this analysis and the apparent molecular weight by sodium dodecyl sulfate gel electrophoresis and gel filtration, a chain length of about 80 residues was calculated. Among the tryptic peptides one blocked heptapeptide was found. Cleavage of this peptide with thermolysin gave two peptide fragments, one of which was not retained on a cation exchange resin. Mass spectrometric sequence determination of this peptide revealed the structure Ac-Ala-Glu-Asp for the N-terminus of polypeptide VII. Treatment with carboxypeptidase A at two different pH values showed that the C-terminal amino acid is isoleucine and the penultimate amino acid is lysine.

The sequence determination of polypeptide VII from beef heart cytochrome c oxidase is described. The amino acid sequence is deduced from overlapping tryptic peptides and peptides obtained after cleavage with Staphylococcus aureus protease. The protein consists of 85 amino acids corresponding to a Mr of 10026, in agreement with a value of 9500 obtained by sodium dodecyl sulfate gel electrophoresis. The amino acid sequence around the only methionine present is very similar to sequences around the invariant heme binding methionine of the cytochrome c family. This similarity suggests that the protein is one of the heme bindings subunits of the oxidase.

The O2 and CO Bohr effects of monomeric and dimeric hemoglobins of the insect Chironomus thummi thummi were determined as proton releases upon ligation. For the O2 Bohr effect of the monomeric hemoglobin III a maximum value of 0.20 H+/heme was obtained at pH 7.5. Upon ligation with CO, however, only 0.04 H+/heme were released at the same pH. In agreement with this finding isoelectric focusing experiments revealed different isoelectric points for O2-liganded and CO-liganded states of hemoglobin III. Analogous results were obtained in the cases of the monomeric hemoglobin IV and the dimeric hemoglobins of Chironomus thummi thummi; here O2 Bohr effects of 0.43 and 0.86 H+/heme were observed. For the corresponding CO Bohr effects values of 0.08 and 0.31 H+/heme were obtained respectively. On the basis of the available structural data the reduced CO Bohr effect in hemoglobin III is discussed as arising from a steric hindrance of the CO ligand by the side chain of isoleucine-E11, obstructing the movement of the heme-iron upon reaction with carbon monoxide. It should, however, be noted that ligands, according to their different electron donor and acceptor properties, may generally induce different conformational changes and thus different Bohr effects, in those hemoglobins in which distinct tertiary and/or quaternary constraints have not evolved. The general utilization of CO instead of O2 as allosteric effector is ruled out by the results reported here.

If one asks, which criteria might be mandatory for the opinion on an enzyme complex, the function of which is not yet fully understood, the integral stoichiometry of all components of the isolate must be considered a guideline for preparation and purification besides known enzymatic activities and pertinent spectral properties. Application of this principal chemical rule is especially necessary in those fields of work, where our methods leave doubt, whether what we obtain is a faithful representation of what exists in nature. This is the case with the respiratory enzyme complexes, e.g. mitochondrial cytochrome c oxidase. The solubilisation and purification of this enzyme from the mitochondrial (or bacterial) membrane has in many cases not met the above criterion. The complete proteinchemical description of the so far most complex type of this enzyme, obtained from bovine heart, and its comparison with simpler eucaryotic and procaryotic oxidases defines the structure of integral preparations more precisely and at the same time is a guide to the function.

In recent years, aminoacid sequence analysis has been extended to hydrophobic proteins, especially those which are constituents of biological membranes and are known as integral or intrinsic membrane proteins. Both expressions refer to the fact that parts of the structures of such proteins extend into and more often penetrate the lipid bilayer of biomembranes, giving rise to a firm association between the hydrocarbon chains of the fatty acids or cholesterol and protein domains made up from about 12 mostly hydrophobic amino acids out of the 20 known to build the protein structure. Integration of these residues into the membrane — most often in ~20-membered helical conformation — is governed by the free energy (-ΔG) of their transfer from a random coil configuration in the aqueous phase into an ordered (helical) conformation in the lipid phase [1].

For the monomeric hemoglobins III and IV and the dimeric hemoglobins of Chironomus the tryptophan circular dichroism reports different conformational response to binding of different ligands. The fine structure bands at 292 nm are most strongly developed in the unliganded state and considerably reduced in the oxy form. The spectrum of the CO derivative is intermediate but clearly more deoxy-like. This finding correlates well with the corresponding Bohr effect magnitudes determined by measuring proton release upon ligation. Infrared difference spectroscopy on O2versus CO derivatives in aqueous solution shows a normal O2 stretching band position at 1107 cm−1 characteristic of asymmetric oxygen binding. The CO stretching band, however, is consistently blue-shifted by 11–13 cm−1 from the 1951 cm−1 position observed with mammalian hemoglobins, indicating reduced CO binding strength. Structural factors relevant to an explanation of the observed phenomena are discussed.

Subunit II of cytochrome-c oxidase contains a redox centre, CuA, with unusual spectroscopic properties; this site consists of two copper atoms and acts as the entry point for electrons from cytochrome c. We have constructed a site-directed mutant of cytochrome-c oxidase from Paracoccus denitrificans in which the CuA site has been disturbed by replacement of Met227 with isoleucine. The purified, fully assembled enzyme complex has been investigated with various techniques including metal analysis, EPR and visible spectroscopies, steady-state and fast kinetics. The stoichiometry of the metals in the enzyme remains unchanged but a clear perturbation of the CuA site can be observed in the EPR and near-infrared optical spectra. It is concluded that in the mutant CuA is still binuclear but that the two nuclei are no longer equivalent, converting the delocalized [Cu(1.5)....Cu(1.5)] centre of the wild type into a localized [Cu(I)....Cu(II)] system. Changes in the overall kinetics of the mutant are correlated with a diminished electron transfer rate between CuA and heme alpha.