[Specific binding of fluorescein bimercuric acetate by histidine decarboxylase from Micrococcus]

The SH-groups of histidine decarboxylase were modified by means of fluorescent probe--fluorescein bimercuric acetate (FMA). Native histidine decarboxylase bound 3 molecules of FMA with complete inhibition of the enzymatic activity. Binding of FMA with the enzyme was accompanied by distinct alteration in absorption and fluorescence spectra. The FMA was also used in studies of SH-containing peptides of histidine decarboxylase; acid SH-peptides obtained after tryptic hydrolysis appears to contain the cysteine of the enzyme active site.