Analogues of 1, 2-propanediol, inactivators of dioldehydrase I. Studies on the effect of 3-halo-1, 2-propanediols on the coenzyme B_(12) dependent dioldehydrase reaction II. Studies on the effect of an epoxide on dioldehydrase

Abstract

PART I: 3-Chloro-1, 2 -propanediol, 3 -bromo-1, 2-propanediol, and 3-iodo-1, 2-propanediol have been found to bind to dioldehydrase. Dissociation constants are approximately equal in each case. Binding occurs in a manner similar to that of the normal substrate, 1, 2-propanediol. All three compounds behave as competitive inhibitors while 3-chloro-1, 2-propanediol and 3-brom-1, 2-propanediol inactivate the holoenzyme as well. This inactivation process is irreversible and may involve the alkylation of sulfhydryl residues of dioldehydrase. Of the above compounds, only 3-chloro-1, 2-propanediol is converted to product; possibly β-chloropropionaldehyde is formed. PART II: 2, 3-Epoxypropanol (glycidol) has been found to bind to dioldehydrase. Its calculated dissociation constant is 8.8 X 10^(-4) M. It binds to dioldehydrase even though it has but one hydroxyl group. 2, 3-Epoxypropanol behaves as a competitive inhibitor. This compound also inactivates the holoenzyme. Unlike the compounds studied in Part I, it also inactivates the apoenzyme, although at a slower rate. Since epoxides are known to alkylate sulfhydryl groups, the above result suggests the presence of exposed sulfhydryl residues.