抄録
The functional groups of the plant myrosinase was investigated using reagents which discriminate the states of amino acids in protein. The enzymatic activity was inhibited by fluorodinitrobenzene (FDNB), trinitrobenzenesulfonic acid (TNBS) and monochlorotrifluoro-p-benzoquinone (CFQ), which are specific reagents for amino group, p-mercuribenzoate (PCMB) and 5-5'-dithio-bis-(2-nitrobenzoic acid), specific for -SH group, and p-diazobenzenesulfonic acid, specific for imidazole group. The rates of inhibition by FDNB and TNBS were accelerated by the addition of ascorbic acid (10-3M). The enzyme was inactivated when five amino groups of the enzyme reacted with CFQ. The enzyme was also inactivated when two -SH groups reacted with Ellman reagent, although four -SH groups were found by Ellman reagent in the denatured enzyme by SDS.
Plant myrosinase was found to be quite sensitive to photooxidation catalyzed by methylene blue. Amino acid analysis indicated that loss of the activity was due to degradation of histidyl residue of the enzyme. These results suggest that amino group, -SH group and histidyl residue constitute the active sites of the enzyme.
