What is the purpose of LD in the kinetic method of Henry for AST?

In the context of the kinetic method of Henry for measuring AST (aspartate aminotransferase), the role of LD (lactate dehydrogenase) is critical for ensuring the accuracy and efficacy of the assay. The correct choice highlights that LD rapidly exhausts endogenous pyruvate during the lag phase of the reaction.

During the kinetic assay, the initial phase often experiences a buildup of substrates and products, which could interfere with accurate measurements. By depleting endogenous pyruvate, LD helps to mitigate the risk of product inhibition. This action not only prevents the buildup of pyruvate but also stabilizes the reaction environment, allowing for a clearer monitoring of AST activity as changes in absorbance can be detected more precisely without the interference of excess substrates. This is crucial for maintaining the integrity of the assay and ensuring that the measured activity reflects the actual enzyme kinetics.

The other choices, while they discuss important aspects of enzymatic reactions and product interactions, do not accurately describe the specific role of LD in this method. For instance, the generation of NADH is critical in other biochemical reactions, but the focus in this context is specifically about controlling substrates and preventing inhibition, which is why the function of exhausting endogenous pyruvate is vital.