Thiol-catalyzed formation of lactate and glycerate from glyceraldehyde.
The formation of lactate from glyceraldehyde is catalyzed by the thiol, N-acetylcysteine, at ambient temperature in aqueous sodium phosphate (pH 7.0). The rate of lactate formation is more rapid at higher concentrations of sodium phosphate and is essentially the same in the presence and absence of oxygen. The formation of lactate is efficient, but proceeds slowly with an 8.8% yield of lactate after 16 days from 10 mM glyceraldehyde in the presence of 12.5 mM N-acetylcysteine and 500 mM sodium phosphate (pH 7.0). The formation of glycerate from glyceraldehyde, that occurs in the presence of oxygen and to a small extent when oxygen has been removed, is also catalyzed by the thiol, N-acetylcysteine, under the same conditions. The dramatic increase in the rate of glycerate formation that is brought about by the thiol, N-acetylcysteine, is accompanied by an equally dramatic decrease in the rates of production of glycolate and formate. Presumably, the thiol-dependent formation of lactate and glycerate occurs via their respective thioesters. The significance of these reactions to molecular evolution is discussed.