Enzyme Mechanism - Examples
We discussed dehydrogenases as having two domains one for NADH binding and one for other substrate in lecture 10. These enzymes often have the ability to make stereospecific products like L-malate and L-lactate. How is stereospecificity achieved in dehydrogenases? For lactate dehydrogenase (LDH), Arg-171 holds the carboxylate group of pyruvate (CH3-CO-COO-) while His-195 provides a proton to the carbonyl on carbon-2 to make the stereospecific product.
Figure 12. Interconversion of Pyruvate/NADH and Lactate/NAD+/H+ catalyzed by lactate dehydrogenase (LDH).
Figure 13. The active site of LDH showing NADH and pyruvate bound by various amino acid side chains.
Figure 14. Model of LDH Catalytic Mechanism showing stereospecific transfer of hydride anion from NADH to pyruvate which is held in position by Arg-171 side chain.
Figure 15. More general view of the LDH Catalytic Mechanism showing the role of specific amino acid side chains.
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©Wilbur H. Campbell, 1995; wcampbel@mtu.edu