Lactate dehydrogenase catalytic efficiency

Feeney, R., Clarke, A. R. Holbrook, J. J. (1990). A single amino acid substitution in lactate dehydrogenase improves the catalytic efficiency with an alternative coenzyme. Biochemical and Biophysical Research Communications, 166, 667-72. 

Place, A.R., and D.A. Powers (1979). Genetic variation and relative catalytic efficiencies lactate dehydrogenase-B allozymes of Fundulus heterocli-tus. Proc. Natl. Acad. Sci. USA 76 2354-2358. 

Molecular hydrogen is not very efficient in direct reduction of NAD+ and NAD(P)h however, can be used in coupled systems for regeneration of a hydrogen donor. As an example, pyruvate was catalytically hydrogenated to lactate, and the latter served as a hydrogen donor in the lactate dehydrogenase (LDH)-catalyzed regeneration of NADH [333] (Scheme 3.53). 

There have been extensive discussions in the literature regarding maximization of the catalytic efficiency of enzymes and the value of their internal equilibrium constants is the equilibrium constant between substrates and products of the enzyme when all are bound productively) (98-102). For example, the value of A int is near unity for both liver alcohol dehydrogenase (78) and lactate dehydrogenase (103) when measured with their natural substrates. The ability of these same enzymes to function with alternative substrates with widely differing external equilibrium constants raises important questions regarding the relationships of the internal thermodynamics of such reactions. 

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