Reaction mechanism of lactate dehydrogenase

Abstract

The hepatic and renal lacticdehydrogenases of the chicken and the pig respectively, whilst showing a notable difference in their isoenzyme composition (one isoenzyme in the one belonging to the liver, and five ín the renal one), present a preponderance of H subunits according to the analogy in the valúes of their real kinetic parameters, and inhibition due to excess of their piruvate and lactate substrates.

According to Cleland’s theoretical predictions, the enzyme of both origins adapts itself to a sequential ordered mechanism classiníƒed as «bi-bi», the cofactor being the first substrate to be added, with the existence of at least two central ternary complexes.

This mechanism implies the existence of three essential active centres in the enzymatic molecule, in which piruvate and lactate occur together, whilst the cofactors are situated in a common active centre.

The balance constant of the system at pH 7.4 indícales that the reaction favours the formation of lactate and NAD, independen! of the isoenzyme composition.

The analogy in the valúes of the real parameters, in the inhibition by substrate and the reaction mechanism, would appear to suggest that kinetic behaviour is independent of the organ and species, and dependes fundamentally on the kind of predominant subunits.