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The PsbP protein is a thylakoid lumenal extrinsic subunit of photosystem II (PSII) specifically found in green plants, such as higher plants and green algae. The binding site of PsbP in PSII has not been determined because of the lack of the high-resolution 3D structure of green plant PSII. Recent studies indicate that the PsbR protein, which is specific to higher plants, is involved in the PsbP binding to PSII; however, the role of PsbR has not been clarified yet. In this study, we showed that PsbR was fractionated differently from PsbP when thylakoid protein complexes were solubilized and separated by sucrose density gradient ultracentrifugation. On the other hand, PsbP was dissociated more easily from the thylakoid membranes in Arabidopsis mutant lacking PsbR than in the wild type, when thylakoid membranes were washed by low-pH buffers or high-NaCl containing buffers. These results suggest that PsbR is not essential but has an auxiliary role for the PsbP binding to PSII.

Due to their superior electronic properties, carbon nanotubes are considered as specific candidates for future nanoelectronics. In this chapter we demonstrate that carbon nanotube-based field-effect transistors with an excellent electrical performance can be assembled bottom-up by applying alternating-current dielectrophoresis which constitutes a huge step forward into the direction of application of carbon nanotubes. Dielectrophoresis is known as a versatile tool for the manipulation of suspended particles in electrical fields. Here we use dielectrophoresis for various tasks related to the development of self-assembly strategies for the fabrication of carbon nanotube-based field-effect transistors: (1) Assembly of interconnects in a very controlled manner, (2) sorting of carbon nanotubes according to their electronic type and (3) reduction of the high contact resistance between the electrodes and the CNT by applying a second dielectrophoresis step with aqueous metal salt solutions.

Sedimentation equilibrium methods which are able to establish a solubility gradient for inorganic species in an ultracentrifugal field are presented. These methods are generally based on the concepts of density gradient and sedimentation equilibrium ultracentrifugation. However, in addition to the formation of a density or an equilibrium gradient, physicochemical parameters such as the pH or the solvent quality are varied throughout the solution column if appropriate high-density or high-molar-mass solutes are chosen or a mixture of solvents with different density is applied. This is demonstrated for two types of solubility gradients including for the case of a pH gradient; parameters for the adjustment of the overall pH are discussed. pH gradients were formed up to 3 pH units and are sensitive to addition of electrolytes, so they can only be applied to sparingly soluble salts. The gradual variation of the solubility of inorganic particles leads to the dissolution of the particles upon sedimentation when the dissolution point is reached. The ionic species formed show increased diffusion compared to the sedimenting particles, so they can diffuse back to regions of lower solubility and thus form a crystal again. This finally leads to an equilibrium situation for the critical crystal nucleus. In the case of a pH gradient with CdS, it is demonstrated that a transition from particles to dissolved ions indeed takes place and can be monitored in the analytical ultracentrifuge. For BaCrO4, the transition to the more soluble BaCr2O7 with decreasing pH can readily be monitored via the associated spectral changes, clearly demonstrating the possibility to perform chemical reactions in a pH gradient.

Comamonas acidovorans, formerly Pseudomonas acidovorans (ATCC 15668) (Tamaoka et al. 1987), possesses a regularly arrayed surface protein (Fig.1) which is packed in a simple “cobblestone” fashion. The p4 lattice has a centre-to-centre spacing of 11 nm (Chalcroft et al. 1986). This structural motif occurs in several species of the β-subdivision of purple bacteria (Fig.2) (Acker et al. 1975, Beveridge and Murray 1975, 1976, Lapchine 1979, Wells et al. 1983).

Mice selectively bred to produce low affinity antibodies are more susceptible to immune complex glomerulonephritis induced by daily injections of a foreign protein antigen than are mice selected to produce high affinity antibody. Development of disease is associated with an inability to produce the normal maturational switch from low to high affinity antibody. Low affinity NM mice, selected by their failure to show affinity maturation after injection of adjuvantised antigen showed an even greater susceptibility to disease. Sucrose density gradient ultracentrifugation studies showed that immune complexes formed in high affinity mice were large (19 S) and cleared rapidly from the circulation. Immune complexes in low affinity mice were significantly smaller. We propose that immune complex diseases may result from an inherited or acquired form of immunodeficiency favouring a predominantly low affinity antibody response. Immune complexes formed from low affinity antibody have a tendency to dissociate and form small (12–17 S) complexes in antigen excess which may deposit in filtering membranes such as the renal glomerulus.

Little is known on the organization of the apolipoproteins on the plasma high density lipoproteins (HDL) surface and on the factors controlling the mass distribution of these apolipoproteins and their role in HDL structure and function. In a previous study using as a model system canine HDL, we showed that apo. A-II. because of its greater affinity for the hydrophilic-hydrophobic interface, can displace apo A-I from the HDL surface in a process which is not attended by a loss of lipids (1). We have now experimental evidence that the monomeric form of apo A-II, either reduced and carboxymethylated (RCM) human apo A-II or rhesus apo A-II,exhibit the same action. Fig. 1 shows the density gradient ultracentrifugation profile of an incubated mixture of canine HDL and human lipid-free apo A-II (B) or its monomeric counterpart (RCM apo A-II) (C). In this example the experimental conditions were chosen so that the amount of human apo A-II in the system was just enough to occupy the surface of canine HDL according to previous theoretical considerations (2,3). It is evident that in both cases at the end of the centrifugal run all of the apo A-II banded in the HDL region whereas the displaced apo A-I was near the bottom of the gradient.

Detection of satellite DNAs was stimulated by the development of density gradient ultracentrifugation methods. Equilibrium ultracentrifugation in the density gradient suggested by Meselson and co-workers (Meselson et al. 1957) is one of the most valuable methods of DNA fractionation and characterization. The method is based on the equilibrium distribution of the macromolecular material in the density gradient by sedimentation of a low molecular substance solution in a constant centrifugal field. At equilibrium, a stable concentration gradient of the low molecular substance is formed under the effect of two opposite actions: sedimentation and diffusion and, as a result, a gradual increase of density is observed towards the direction of the centrifugal force. The initial concentration of the low molecular substance, the centrifugal field, and the height of the liquid column can be so selected that at equilibrium the macromolecules will be pooled into the density gradient zone. The centrifugal field directs the macromolecules to a region where the sum of the forces acting on a given molecule is equal to zero. This tendency is opposed by the Brownian motion, and as soon as equilibrium is reached, the macromolecules form a zone in the density gradient, with a width inversely proportional to the molecular weight (Fig. 1).

Of the methods to measure VLDL triglyceride (TG) turnover in humans, the simplest is that utilizing 3H-glycerol. We showed that when simultaneous measurements were made with the radioglycerol method and the lipolytic rate method, a method which depends on different assumptions, similar turnover rates were obtained (Steiner and Murase, 1975). This paper will describe how the radioglycerol procedure has been used in humans in order to determine 1) whether VLDL behaves as a single homogeneous pool, 2) whether large VLDL is the only precursor for small VLDL, 3) whether LDL-TG is derived only via the smallest VLDL particles, and 4) the proportion of VLDL-Tg glycerol derived from plasma glycerol.

Currently the most widely used rabies vaccines for man are produced in animal brain tissue. Immunization with these vaccines can result in severe neurologic reactions. On the other hand the highly immunogenic and safe human diploid cell vaccine (HDCV) is difficult to produce and comparatively expensive.

The pseudomicellar (apolar core, polar surface-shell) model for spherical lipoproteins occurring in normal blood plasma provides a useful framework for evaluating the metabolism of the various lipid and protein components of triglyceride-rich lipoproteins. Available evidence indicates that this basic structure is retained from the time that the synthesis of these particles is completed in the Golgi apparatus of the cells of origin until they are finally taken up by the liver or transformed to low-density lipoproteins. Available evidence indicates that this basic structure is retained from the time that the synthesis of these particles is completed in the Golgi apparatus of the cells of origin until they are finally taken up by the liver or transformed to low-density lipoprotein. If this is so, it follows that the fractions of particle volume occupied by core and surface-shell of individual particles are essentially fixed by their size (1). Much of the surface-shell is composed of phospholipids, particularly in particles in the upper size range; proteins and cholesterol comprise an increasing fraction as size decreases.

Previous studies have established that low density lipoproteins (LDL) incubated with malondialdehyde (MDA) and oxidized LDL undergo extensive modification in structure and are specifically recognized by the acetyl-LDL receptor of the macrophages (Fogelman et al. 1980; Henriksen et al. 1981; Steinbrecher et al. 1985). Oxidatively modified LDL are also potentially toxic to endothelial cells (Hessler et al. 1983). The addition of pantethine [D-bis(N-pantothenil-B-aminoethyl)-disulfide] in vitro during the incubation of LDL with O2 prevents the increase of the electrophoretic mobility, the increase of MDA content and the appearance of apoB aggregates in oxidized LDL (Bittolo Bon et al. 1985). The aim of the study was to assess the effect of treatment with pantethine in modifying the LDL peroxidation in vitro. Moreover, the effect of the drug on an LDL subfraction was studied, which was by ion exchange chromatography, that according to our data represents on aliquot of human LDL peroxidized in vivo.

Isothermal calorimetry measures the enthalpy change involved in a chemical reaction. When adapted to the microscale, it quantitates the amount of millijoules associated at a given temperature with the mixing and reassembly of biochemicals, i.e., in our case an apoprotein solution and a phospholipid dispersion. The extent of reassembly and the complex composition can be derived from density gradient ultracentrifugation experiment performed in parallel with the microcalorimetric measurements (Rosseneu et al., 1974).

The difference in relative biological activity between isolated chemically purified endotoxic lipopolysaccharide (LPS) and endotoxins generated in situ with intact bacteria used in models of pathogenic infection is an important consideration for interpretation of experimental studies of pathogenesis. We have addressed this problem by establishing an in vitro model in which endotoxins are generated in their normal state following phagocytosis of intact bacteria. These studies have been facilitated by labeling specifically the LPS component of E. coli with tritiated galactose by growing an expimerase deficient strain of this organism in the presence of 3H-galactose. Macrophages are allowed to phagocytose the organisms for several hours followed by removal of unphagocytosed E. coli. This procedure results in more than 90% of the macrophage associated labeled bacteria being internalized. After 48–72 h of subsequent incubation, the radiolabeled material is harvested from the culture supernatant and from macrophage lysates. A partially purified LPS is obtained by phenol-water extraction. As a control in these studies, E. coli organisms are incubated with culture medium and then subjected to phenol-water extraction. The extracted LPS is purified by isopycnic density gradient ultracentrifugation to obtain LPS free from the majority of non-LPS-associated components.

Photosystem I (PS I) particles were isolated from sorghum thylakoids by Triton-X-100 solubilisation. The purified photosystem I particles possessed a chlorophyll/P700 ratio of 180 and a chlorophyll a/b ratio of 10. The polypeptide composition of the isolated PS I complex revealed a dominant 68kD polypeptide, four polypeptides in the range of 18–25kD associated with LHC-I and six minor polypeptides in the range of 8–24kD. The chlorophyll-protein (chl-protein) complexes of PS I were isolated from the purified particles by centrifugation in SDS sucrose density gradients. The complexes were designated as CP I, CP Ia and LHC-I. Sucrose density gradient ultracentrifugation resulted in two chlorophyll protein complexes associated with LHC-I-730 which were identified by their fluorescence emission spectra.

Previous studies from this laboratory have demonstrated the existence of a minor fraction of macrophage RNA which has a banding density in cesium sulphate solution lighter than that of the bulk of the cellular RNA (Gottlieb et al., 1967). If rat macrophages are exposed to T2 bacteriophage, nearly all of the immunogenic activity attributed to the RNA of the macrophage is found in the minor light density fraction. The immunogenic activity of the minor band, as well as its ability to band in a cesium sulphate density gradient, is destroyed by incubation with pronase. This report presents additional information regarding the purification of this minor RNA-protein complex of macrophages and the determination of some of its properties.