Abstract
Summary
The inhibition of tryptophan pyrrolase in vitro by plasma and certain other native substances was investigated in an attempt to elucidate mechanisms responsible for the assumed decrease in activity of this enzyme in vivo during endotoxin poisoning. Results of kinetic studies eliminated the plasma inhibitor as a causal factor in the irreversible decrease in activity of tryptophan pyrrolase in whole homogenates of liver from endotoxemic mice. The enzyme was found to be inhibited by citrate, the concentration of which increased substantially in the liver during endotoxicosis. Unlike inhibition by plasma, citrate inhibition could not be reversed by excess hematin cofactor. It was therefore concluded that at least part of the decreased activity of tryptophan pyrrolase in whole homogenates of poisoned mice may be the result of inhibition by citrate.
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