Formation of the Michaelis complex without involvement of the prosthetic group dehydroalanine of histidine ammonialyase

The dehydroalanine-less S143G mutant of histidine ammonia-lyase was constructed and used for kinetic measurements with 5'-nitro-histidine as a substrate. The natural substrate histidine turned out to be a competitive inhibitor of the mutant enzyme and exhibited a K-i value which was similar to its K-m value with the wild-type enzyme. Thus the dehydroalanine prosthetic group does not play a role in formation of the Michaelis complex. (C) 1997 Elsevier Science Ltd.