Abstract:
In recent years it has been recognised that metal ions must play an important role in enzymatic reactions. A large number of enzymes are known to have metal ions associated with them, and the presence of these ions is necessary for the enzymes to exhibit catalytic activity. Among the most common Dixon and Webb, Enzymatic Reactions, 2nd Ed. Longmans 1964. of these metal ion cofactors are: manganese(II), magnesium(II), calcium(II), copper(II), iron(II), nickel(II), cobalt(II), and zinc(II). This interesting observation has aroused much speculation as to the mechanism of metal ion activation of enzymes. Several non-enzymatic reactions are catalysed by transition metal ions and these make interesting model systems for the enzymatic reactions.
Metal ions may exhibit catalytic activity in two distinct types of reaction in homogeneous systems:
(a) Reactions in which a valency change occurs in the metal ion.
(b) Reactions in which catalysis is due to the initially fast formation of a complex between metal ion and substrate followed by some reaction of this complex, which does not involve a change in the valency state of the metal ion.
