title: Kinetics of alpha-dicarbonyls reduction by L-glycol dehydrogenase from hen muscle.
abstract: Michaelis constants of L-glycol dehydrogenase from hen muscle (isozyme of pI 7.2) for the alpha-dicarbonyls tested (glyoxal, 2,3-pentanedione, methylglyoxal, and diacetyl) range from 35 microM for pentanedione to 0.41 mM for glyoxal. The enzyme shows a high affinity for NADPH, Km (2.2-3.1 microM), and Ks (1.2-1.9 microM) being so much lower than its tissue concentration that L-glycol dehydrogenase has to operate in vivo saturated with the coenzyme; this condition is very unfavorable to play a role in regulating the equilibrium oxidized/reduced forms of the pyridine nucleotides, as it has been proposed for some similar enzymes. Convergence of the double reciprocal plots and the pattern of inhibition by products and by acetone, a substrate analog, demonstrate that glyoxal reduction--and most likely that of diacetyl--proceeds via an ordered Bi-Bi mechanism in which NADPH is fixed before the addition of the carbonyl; the reduction of methylglyoxal and 2,3-pentanedione could follow the same model, but our experimental results are also consistent with that of Theorell-Chance.
mesh_terms: D000429:Alcohol Oxidoreductases / Q000378:metabolism*; D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D002645:Chickens; D003931:Diacetyl / Q000378:metabolism; D005260:Female; D007659:Ketones / Q000378:metabolism*; D007700:Kinetics; D009132:Muscles / Q000201:enzymology*; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D010422:Pentanones / Q000378:metabolism; D011765:Pyruvaldehyde / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D007659:Ketones; D010422:Pentanones; D009249:NADP; D011765:Pyruvaldehyde; D000429:Alcohol Oxidoreductases; C031043:L-glycol dehydrogenase; D003931:Diacetyl; C013186:2,3-pentanedione