The stereochemical courses of the reactions catalyzed by serine hydroxymethyltransferase (EC 18.104.22.168) and 5,10-methylenetetrahydrofolate dehydrogenase (EC 22.214.171.124) have been determined. The method employed was to prepare the labeled intermediates (6R,11R)- and (6R,11R)-5,10-methylene[l l-1H,2H]tetrahydrofolate by stereospecific chemical reduction and to determine their absolute stereochemistry at Cl 1 by the measurement of proton nuclear Overhauser enhancements (NOE's). Correlation of these results with those obtained by generating (6R)-5,10-methylene[l l-1H,2H]tetrahydrofolate enzymatically from (3S)- and (3R)-[3-1H,2H]serine with the transferase and from (6R)-5,10-methenyl[ll-2H]tetrahydrofolate via the dehydrogenase delineated the stereochemical paths of both enzymes. Serine hydroxymethyltransferase converts (3S)- and (35)-[3-1H,2H]serine to (65,1 15)- and (6R,11R)-5,10-methylene[l l-1H,2H]tetrahydrofolate, respectively, and the dehydrogenase stereospecifically removes HR. These results also were correlated with those obtained by Tatum et al. [Tatum, C. M.; Vederas, J.; Schleicher, E.; Benkovic, S. J.; Floss, H. G. J. Chem. Soc. Chem. Commun. 1977, 218–220] on thymidylate synthetase (EC 2.1.1.b) to further delineate the stereochemical course of the one carbon unit transfer and accompanying reduction catalyzed by that enzyme.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry