[Study of the role of histidine residues in the function of uridine phosphorylase from Escherichia coli K-12 by protein engineering].

Using site-directed mutagenesis, mutant genes of the E.coli UDPase that coded proteins with point substitutions of histidine residues (i.e., H8N, H47N, H101N, H122N, H152N, H179N, and H240N) were constructed. Study of the enzymatic activity of mutant UDPases showed that histidine-asparagine substitutions at the positions 47, 101, 152, 179, and 240 do not affect protein functioning. Whereas H122N and H8N substitutions inhibit the activity of UDPase by 60 and 100%, respectively. This evidences the important functional role of the His122 and His8 residues for the formation of the active site fo the enzyme.