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 Ki value which was similar to its Km value with the wild-type enzyme. Thus the dehydroalanine prosthetic group does not play a role in formation of the Michaelis complex.