FORMATION OF THE MICHAELIS COMPLEX WITHOUT INVOLVEMENT OF THE PROSTHETIC GROUP DEHYDROALANINE OF HISTIDINE AMMONIA-LYASE

The dehydroalanine-less S143G mutant of histidine ammonia-lyase was co nstructed and used for kinetic measurements with 5'-nitro-histidine as a substrate. The natural substrate histidine turned out to be a compe titive 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 dehyd roalanine prosthetic group does not play a role in formation of the Mi chaelis complex. (C) 1997 Elsevier Science Ltd.