Metal Ions in Enzymes Using Ammonia or Amides

Abstract

A variety of enzymes important in the utilization, production or transfer of ammonia was examined. Several were found including the L-histidine and L-phenylalanine ammonia-lyases and some enzymes that utilize glutamine or ammonia in amidotransferase reactions, all of which show evidence for the involvement of as yet unreported transition metal ions in their mechanism of action. Catalysis by metalloenzymes may be a reflection of the chemistry of the metal ion itself as a Lewis acid. Perhaps too much emphasis has been placed on supposed special characteristics (such as strain, entasis) of the enzyme-metal ion association. The mechanism of catalysis of hydrolysis of specific substrates by carboxypeptidase A was discussed.