ABSTRACT Isolated and hydrated complexes of the substrate (pyruvate) and inhibitor (oxamate) of lactate dehydrogenase (LDH) with imidazole and/or the guanidinium cation (models of the LDH pocket) were studied using the quantum-chemical methods (HF/6-31++G** and PCM(water)//HF/6-31++G**). For comparison, isolated and hydrated complexes of pyruvic and oxamic acids with imidazole and/or guanidine were also analysed at the same levels of theory. The calculations show that complexes of anions are more stable in water than complexes of acids. The estimated formation constants for complexes of oxamate are greater than those of pyruvate. This suggests that the inhibitor interacts with stronger strength with the LDH pocket than the substrate.
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