3-Deuterio-L-malic acid obtained from the fumarase catalyzed hydration of fumaric acid in D 2O is shown to have the erythro configuration by n.m.r. comparison with stereospecifically synthesized threo-3-deuterio-DL-malic acid. The fumarase and aspartase systems thus operate by a trans mechanism as do the β-methylaspartase and cis-aconitase systems. Brewster's rules are applied to the problem of the stereochemistry of citric acid synthesized in the Krebs cycle and a configuration related to D-malic acid is arrived at. This configuration plus the α Ds,β Ls configuration of d-isocitric acid permits depiction of the stereochemical pathway of the cis-aconitase system and of the reactions of the Krebs cycle. The possibility that cis-aconitase exhibits a preferred direction for addition of OH, with concomitant trans addition of H, is discussed.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of the American Chemical Society|
|State||Published - 1961|
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