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PubMed1980

[Proteolysis as an approach to the study of protein distribution in the membrane of Micrococcus lysodeikticus].

Treatment of M. lysodeikticus protoplasts with subtilisin or pronase did not affect their permeability and led to a digestion of 20--30% of protein. DS-Na electrophoresis of protoplast membranes resulted in disappearance of three protein bands. This suggests that the outer surface of M. lysodeikticus protoplasts contains three proteins other than respiratory chain enzymes, which are subjected to an attack by proteinases. Treatment of the M. lysodeikticus membranes, isolated by osmotic shock, with proteinases resulted in a digestion of 20--50% of protein. The factors preventing the interaction between the membrane components (e.g. decrease of Mg2+ concentration, ultrasound, KCl, EDTA and particularly detergents) favoured the proteolysis; however, the bulk of the proteins remained insensitive to the effect of proteinases. The membranes pretreated with DS-Na or chlorophorm--methanol mixture proved to be good substrates for proteinases. Treatment of the membrane fraction with proteolytic enzymes allowed to obtain some data on localization of respiratory chain enzymes in the membrane stroma of M. lysodeikticus. Thus, cytochrome c is localized nearer to the membrane surface than cytochromes a and b, while malate dehydrogenase is plunged deeper into the membrane stroma as compared to NADH dehydrogenase.

Cell Membrane↗
PubMed1981

[Role of tryptophan in the enzymatic activity of histidine decarboxylase from Micrococcus sp. n].

The effect of N-bromosuccinimide (BSI) on micrococcal histidine decarboxylase in 0.07 M phosphate buffer, pH 5.6 was studied. Data from spectral and amino acid analyses suggest that at 20-fold molar excess of BSI three of 12 tryptophane residues undergo selective modification, resulting in 80-85% loss of the enzyme activity. Using fluorescent method and polyacrylamide gel electrophoresis, it was shown that modification of these reactive tryptophane residues does not cause structural changes of the enzyme. Presumably tryptophane residue responsible for enzymatic activity are either located in the enzyme active site of close to it. At 40-50-fold molar excess of BSI 6 to 9 tryptophane and 2 to 3 cysteine residues are subjected to modification; the other 3 tryptophane residues are unaffected by BSI. These are probably located deep inside the histidine decarboxylase molecule. The maximum of the protein fluorescent spectrum during modification of the 40-50-fold molar excess of BSI is shifted towards higher wavelength values, thus suggesting conformational changes of the enzyme. It can be therefore assumed that the enzyme molecule contains at least 2 groups of structurally and catalytically essential tryptophane residues which significantly differ in reactivity. Some diazonium salts were shown to inhibit micrococcal histidine decarboxylase. The kinetics of the inhibiting effect of these compounds were investigated.

Amino Acids↗
PubMed1978

[Has the respiratory chain of Micrococcus lysodeiktocus any redox components on the outer surface of cytomembrane?].

M. lysodeikticus protoplasts have catalyzed the reduction of 5.10(-4) M ferricianide by endogenous substrates if the respiratory chain is inhibited by cyanide or anaerobiosis. A disturbance of the protoplast permeability by osmotic shock or Triton X-100 treatment resulted in the decrease of the endogenous ferricianide reduction rate and in simultaneous stimulation of malate ferricianide reductase activity in dehydrogenase site of the inner membrane surface. Reactivation of endogenous ferricianide reduction by protoplasts and the loss of malate stimulating activity were observed in hyperosmotic medium. Unlike malate oxidation by osmotically shocked protoplasts, endogenous protoplast repiration was resistant to ferricianide 5.10(-4) M). The latter, being added to protoplasts, induced the oxidation of anaerobically reduced cytochromes b556+560, and it practically did not affect cytochromes c552 and a601. The data obtained suggest that at least one of the respiratory chain components is arranged on the outer side of the protoplast membrane. This component is probably located in the cytochrome region. The results obtained confirm the hypothesis on transmembrane organization of the respiratory chain in M. lysodeikticus.

Cell Membrane↗