HETEROGENEITY IN THE RAPIDLY EXCHANGING METALS OF HORSE LIVER ALCOHOL DEHYDROGENASE

Abstract

This chapter discusses heterogeneity in the rapidly exchanging metals of horse liver alcohol dehydrogenase. Liver alcohol dehydrogenase is a metalloenzyme containing four gram atoms of zinc. Two of the zinc atoms are at each of the two catalytic sites while two of the metal atoms are located 20 Å from the catalytic site. The zinc atoms of the enzyme can be partially or completely replaced by cobalt with retention of enzymatic activity. The characteristics of the metals of Co4-LADH represent an average of metal at the catalytic sites and at the non-catalytic sites and, hence, are not useful in differentiating the properties of the two classes of metal in the enzyme. In contrast, cobalt/zinc LADH hybrids in which the site of metal substitution is known are potentially valuable in defining the functional roles of the two classes of metal. The chapter also discusses the spectral and kinetic properties of two hybrid enzymes, CoZn3-LADH and Co2Zn2-LADH in an effort to establish the site(s) of metal substitution.