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The chemical shift of the C-2 imidazole protons of the histidine residues of pancreatic ribo-nuclease has been studied as a function of pH in 2H2O. Upon protonation of the imidazole ring the C-2 proton magnetic resonance signal shifts about 1.0 ppm to a lower field. Thus titration curves and approximate pK values of the histidine residues are obtained. The pK values of histidine 119 and histidine 12 of the active site are unusually low and shift by 1.0 and 0.7 units to higher values when the NaCl concentration is changed from 0.1 M to 0.4 M, whereas the pK value of histidine 105 shifts only by about 0.2 units. This indicates the presence of a positively charged group in the immediate environment of histidine 119 and histidine 12. The abnormal chemical shift of the histidine 48 C-2 proton at low pH is explained by means of an interaction of histidine 48 with the carboxylate anion of aspartic acid 14. From an analysis of the titration curves of histidine 119 and histidine 12 the existence of an enzyme species in which both imidazoles arc connected by a hydrogen bond is derived. The C-2 proton magnetic resonance signals of histidine 119 and histidine 12 shift to a lower field when inhibitors bind to the enzyme. Both histidines are then kept in a protonated form up to the pH range of 7–8. The apparent pK values are higher in the cytidine 2′-phosphate-ribonuclease complex than in the cytidine 3′-phosphate- ribonuclease complex. A similar shift of the histidine 119 and histidine 12 signals is observed with binding of pyrophosphate to ribonuclease indicating that only the phosphate group causes the behaviour of the histidines. Shifts of the C-6 proton magnetic resonance signal of the pyri- midine ring indicate an additional binding of the base to an aromatic side chain of the enzyme. The mechanism for the binding process proposed in previous papers by Witzel and coworkers in which histidine 119 and lysine 41 are the binding groups of the enzyme, whereas histidine 12 takes up a proton when being released from its binding to histidine 119, is in agreement with the results reported in this communication. [ABSTRACT FROM AUTHOR]

The effect of disodium cromoglycate (DSCG) on antigen-evoked histamine release from IgE-sensitized human skin in vitro has been studied using breast skin from six donors. Concentrations of DSCG ranging from 10-200/M did not produce any consistent effect on histamine release, the results ranging from moderate inhibition to moderate enhancement. With higher concentrations of DSCG (400-500 UM) enhancement of release occurred in nearly all experiments. Variation of antigen concentration did not modify the response to DSCG. These results do not support the possibility that DSCG may be effective in the treatment of immediate hypersensitivity reactions in human skin. [ABSTRACT FROM AUTHOR]

The study of the dissociation of Pila leopoldvillensis haemocyanin by means of light scattering has shown that the protein concentration has no influence upon the dissociation into halves and tenths. Different buffer ions were shown to have specific effects upon the dissociation of Pila haemocyanin: with maleate and phosphate the dissociation curves are shifted towards lower pH values; with imidazole and Tris the shift is in the opposite direction. Takening into account the high molecular weight of the protein, the binding of chloride ions, as determined by the ΔHp method, is very small. Therefore pure KCl solutions rather than buffers were used in further work on the dissociation of haemocyanin. In view of these observations an attempt is made to interpret the influence of the pH and ionic strength upon the dissociation-association reaction according to a sequential loop model: the forward and back reaction proceed along opposite sequential pathways, each starting with a particular change of the ionisation state of the wholes, halves or tenths. According to this reaction scheme the ionisation constant of the sites responsible for the dissociation into halves is 6.96; and that for the dissociation of halves into tenths is 9.65. [ABSTRACT FROM AUTHOR]

Crystalline phosphoglucomutase can be activated almost two-fold by preincubation in acid or alkali at optimal pH values of 3.5 and 10.5, respectively. The initial rate of such activation follows first order kinetics. Enzyme concentration affects the rate and extent of activation. This in turn is influenced by the salt concentration of the preincubation medium. Denaturation with loss of enzyme activity usually followed activation. However, stabilization of the activated state could be effected by imidazole, cysteine and EDTA in the presence of Mg2+. In the activated state there was no evidence of change in the molecular weight. [ABSTRACT FROM AUTHOR]

The stability constants of the ternary Cu2+ complexes, ethylenediamine-Cu2+-pyrocatechol and histamine-Cu2+-pyrocatechol dianion, were determined. Both complexes are more stable than one would expect on pure statistical reasons. The imidazole-containing ternary Cu2+ complex is, however, especially stable. For the equilibrium, Cu(histamine)2-+-Cu(pyrocatechol)2 [This symbol cannot be presented in ASCII format]2[(histamine)Cu(pyrocatechol)], the constant is log X = 4.86 (I = 0.1; T = 25°), while the statistical value is 0.6. These results were compared with those taken (or calculated) from the literature; it is concluded that the π-system of the ligands is important for such a great increase in stability. Furthermore, the Cu2+-histamine 1:1 complex selectively binds to O-ligands rather than to N-ligands. Thus, the first coordinated ligand has an influence on the kind of the second to be coordinated, i.e. the Cu2+-histamine 1:1 complex shows discriminating qualities. The significance of these results is discussed with regard to Cu-proteins, sines it is suggested for several enzymes that the imidazole group of histidine is involved with the binding of metal ions. [ABSTRACT FROM AUTHOR]

A series of linear and cyclic derivatives of histidyl-tryptophan was synthesized for the study of intramolecular indole-imidazolium interaction. The absorption spectrum and the fluorescence intensity of each of the peptides were examined in aqueous solution when the imidazole side chain was protonated (pH < 4) and uncharged (pH > 9). The absorption spectra of the protohated peptides show hypochromism around 280 mμ, whereas at shorter wavelengths hyperchromism appears. The hyperchromism is most, intense around 240 mμ and it is attributed to the charge-transfer band of the intramolecular indole-imidazolium complex. The fluorescence intensity of all tested histidyl-tryptophan peptides drops markedly with protonation of the imidazole side chain. The change in fluorescence intensity with pH superimposes to the potentiometric titration curve of the imidazole residue. From the preceeding results it may be concluded that (a) the electron affinity of imidazolium is smaller than that of the positively charged nicotinamide by 1.2 eV and (b) the indole-imidazolium complex is not of a sandwich type. It is suggested that the charge-transfer bond of this complex is located between the C-2-C-3 bond of the indole and the plus charge center of the imidazolium. [ABSTRACT FROM AUTHOR]

Active chloride uptake by cells of Chara corallina decreases as the pH of the bathing solution is increased, using a range of buffers. Superimposed on this effect, large stimulations of Cl[SUP-] uptake can be obtained by the addition of imidazole and tris buffers or ammonium sulphate. 'Stimulated' or 'normal' Cl[SUP-] influxes respond similarly to the presence of metabolic inhibitors. It is suggested that these effects are not due to changes in photosynthesis or respiration, but reflect the dependence of Cl[SUP-] transport on the pH gradient across the plasmalemma. Possible ways in which Cl[SUP-] transport might be linked to H[SUP+] or OH[SUP-] fluxes are discussed. It is proposed that the pH gradient across the plasmalemma is controlled by charge-separating reactions which produce an active H[SUP+] efflux, and that Cl[SUP-] uptake is linked to OH[SUP-] efflux by ion-exchange reactions. The metabolic implications of this scheme are discussed in detail, with reference to previous work on Characean and other plant cells. [ABSTRACT FROM AUTHOR]

This study describes a human IgG autoantibody detected by immunofluorcsccnce, found in four out nf 1410 (O.V',,) mixed hospital patients' sera and which reacted exclusively with tissue mast cell (MC) granules in a non-species specific manner. No reaction occurred with blood basophils. suggesting that their granules differ from those of tissue MC. Experiments so far indicate that the antigen is in the amphophihc protein matrix of the granules. Histamine and 5HT cannot be involved since granules showed positive fluorescence following their release and commercial heparin could not absorb out the fluorescence. The antibodies did not cause MC degranulation or histamine release in vitro and antigenic determinants could not be demonstrated on the MC membrane, unlike similar antibodies produced experimentally. [ABSTRACT FROM AUTHOR]

Incubation of sensitized peritoneal or pleural cells, or isolated mast cells, taken from rats previously infected with the nematode, Nippostrongylus brasiliensis, but not of cells taken from parasite-free controls, with concanavalin A in vitro induces the release of histamine. The release mechanism triggered by Con A is virtually completed within 60 sec, depends on temperature, but not on the presence of complement, and is inhibited by sympathomimetic amines. It therefore shows striking similarities to the anaphylactic reaction induced by the specific allergen. The mechanism by which histamine release is triggered by Con A is discussed, considering the observations that trypsinized Con A is no longer able to induce histamine release, that the presence of high concentrations of trypsinized Con A inhibits the release of histamine by subsequently added Con A or allergen, and that certain carbohydrates inhibit the release of histamine induced by both Con A and allergen. Although some of the data suggest a similarity in the structure of the antigenic determinant in the Fab fragment of IgE and the receptor site for Con A, it seems more likely that Con A is reacting mainly by cross-linking of Fc regions of the immunoglobulin molecule. [ABSTRACT FROM AUTHOR]

The article presents information on a case of hereditary angio-neurotic oedema, successfully treated with ε-amlnocaproic acid. A patient with clinical and laboratory findings characteristic of hereditary angioneurotic oedema was investigated. The patient was observed for a period of 5 weeks, during which he had four attacks. ε-Aminocaproic acid was then given continuously for 5 months, during which time the patient had no attacks. The studies on histamine metabolism revealed no significant changes with the exception of the urinary excretion of histamine, which was moderately increased towards the end of the period studied.

1. Diethylpyrocarbonate reacts specifically with histidine residues in human ceruloplasmin at pH 6. 2. Carbethoxylation of imidazole groups in ceruloplasmin does not affect the optical absorption in the visible region which is due to paramagnetic Type-1 copper or diamagnetic copper, but has a pronounced effect on electron paramagnetic resonance (EPR) spectra of the protein. The ERP-spectral changes do not involve the Type-1 copper signal or a conversion of diamagnetic copper into paramagnetic copper but indicate a change in the binding situation of Type-2 copper. ERP spectra of the modified protein are pH-dependent over the range pH 5-7. Carbethoxylation of ceruloplasmin and the concomitant ERP--spectral changes parallel a decrease in oxidase activity towards ferrous ions and dimethyl-p-phenylenediamine. Inhibition by diethylpyrocarbonate can be (At least partially) reversed by treatment with hydroxylamine at pH 7, which also restores the ERP spectrum of native ceruloplasmin. [ABSTRACT FROM AUTHOR]