The determination of human-serum-cholinesterase activity with o-nitrophenyl butyrate.

Interference with the removal of oxaloacetate through citrate formation would naturally impair the catalytic oxidation of pyruvate. The inhibition of oxygen uptake stimulated by aspartate may well be another consequence of the same effect. A similar explanation can be offered for the inhibitory effect on glutamate oxidation, since oxobutyrate inhibits the removal of oc-oxoglutarate as well. a-Oxobutyrate, which inhibits the utilization of x-oxoglutarate, presumably enhances its formation from added citrate. Montgomery & Webb (1956) have reported a similar effect with another inhibitor of oxoglutarate oxidation, namely parapyruvate, in the presence of which the unaffected sections of the Krebs cycle proceed at a more rapid pace.