DPN-linked sn-glycerol-3-phosphate dehydrogenase. Cyclopentanoid analogues mimic the active rotameric state of the...

Five diastereoisomeric cyclopentane-1,2,3-triol monophosphate analogues of sn-glycerol 3-phosphate have been studied as substrates and inhibitors of sn-glycerol-3-phosphate dehydrogenase (EC 1.1.18) of rabbit skeletal muscle. Of the five analogues, only two were substrates, DL-1,2,3/0-1P (analogue I) and DL-1,2/3-1P (analogue II). The rest were weak competitive inhibitors of the enzyme. Initial rate kinetic studies of the substrate-active analogues analyzed by a rapid equilibrium random-order mechanism showed that Ks (I) = 4.6 +/- 2.6 mM; Ks (II) = 2.2 +/- 0.6 mM compared with Ks (DL-glycerol-3-P) = 2.4 +/- 0.9 mM. Correlation of the structures of the five analogues with their activities indicates that the enzyme requires a syn orientation of the carbon-oxygen bonds about C-2 and C-3 for activity, which is optimized by an anti relationship between the hydroxyl groups at C-1 and C-2 of the cyclopentanetriol monophosphates. These results are used to deduce the conformation of sn-glycerol-3-P as it is bound in the active site of the enzyme.