Evidence for essential histidine and dicarboxylic amino-acid residues in the active site of UDP-glucose: solasodine glucosyltransferase from eggplant leaves

Effects of several chemical probes selectively modifying various amino-acid resi­dues on the activity of UDP-glucose : solasodine glucosyltransferase from eggplant leaves was studied. It was shown that diethylpyrocarbonate (DEPC), a specific modi­fier of histidine residues, was strongly inhibitory. However, in the presence of exces­sive amounts of the enzyme substrates, i.e. either UDP-glucose or solasodine, the in­hibitory effect of DEPC was much weaker indicating that histidine (or histidines) are present in the active site of the enzyme. Our results suggest also that unmodified resi­dues of glutamic (or aspartic) acid, lysine, cysteine, tyrosine and tryptophan are nec­essary for full activity of the enzyme. Reagents modifying serine and arginine resi­dues have no effect on the enzyme activity.