Stereoselective reactivity of the SH groups of yeast glyceraldehydephosphate dehydrogenase in the allosteric T and R states

Abstract

Yeast glyceraldehyde-3-phosphate dehydrogenase as a typical SH enzyme is inactivated by the antipodes of a-iodopropionic acid and its amide at different rates. The apoenzyme reacts faster with the D(+) antipode of the free a-iodopropionic acid (k_D/k_L = 6.8) and the L(−) antipode of the amide (k_L/k_D = 3). On addition of NAD⁺ the stereoselectivity of the SH group towards a-iodopropionic acid is inverted, that towards the amide is enlarged, the rate relationships depending on the NAD⁺ concentration. The results were interpreted by the assumption, that the allosteric T state of the enzyme reacts most rapidly with the D(+) antipodes, whereas the R state favours the L(−) antipodes of the alkylation reagents. The dependence of the reaction rates on the NAD⁺ concentration could be fitted to the allosteric function of state .