CATALYSIS BY METALLOENZYMES.

A brief survey of the roles of metalloenzymes is given documenting their participation in all aspects of cellular metabolism including the biosynthesis and degradation of specific metabolites as well as DNA, RNA and protein synthesis. Focus on the details of a metal-assisted enzyme catalytic mechanism will be illustrated by a Zn metalloenzyme, alkaline phosphatase, which is a dimeric enzyme containing both catalytic and structural Zn(II) ions as well as Mg(II) sites. Substitution of first transition metal ions and Cd(II) for the native Zn(II) ion in this phosphomonoesterase and transferase produces enzymes of widely different turnover numbers and allows the application of optical absorption spectroscopy (Co), ESR (Mn, Co, Cu) and **1**1**3Cd NMR to the determination of the structure of the metal site. The protein structure and metal ligands have been explored by **1**3C and **1**9F NMR using **1**3C and **1**9F labelled amino acids to biosynthesize the protein. The phosphorylated intermediates along the reaction path are present in sufficient equilibrium concentrations to be studied by **3**1P NMR. The resultant detailed description of the active center has been achieved by methods which determine the dynamic solution structure of the molecule and are potentially applicable to many large multimeric metalloenzymes.