[Modification of micrococcal histidine decarboxylase with tetranitromethane].

Tetranitromethane inhibited distinctly the histidine decarboxylase activity at pH above 7.0. Spectral and fluorescence properties as well as amino acid composition of the transformed enzyme were studied. Nitration of tyrosine residues occurred simultaneously with oxidation of cysteine in a molecule of histidine decarboxylase treated with tetranitromethane, while the other amino acids such as tryptophane, histidine and methionine were not altered. The histidine decarboxylase pretreated with dithiothreitol, became insensitive to the tetranitromethane effect but complete inactivation of the enzyme was observed under these conditions. Possible mechanisms of the histidine decarboxylase inactivation are discussed.