Abstract
Rat liver glutathione reductase is markedly inhibited by the isolated reduced B-chain (phenylalanine chain) of insulin. The inhibition is progressive with time, of the irreversible type, and follows the characteristics of a bimolecular reaction. The reaction between enzyme and inhibitor is dependent upon the presence of small amounts of NADPH (>2.2x10-7 M). Reduced glutathione or cysteine completely and rapidly reactivates the enzyme, glutathione being more active than cysteine. Insulin, reduced or sulphonated A-chain of insulin has no effect on the enzyme. The sulphonated B-chain has a slight inhibitory effect. No inhibition is found on yeast glutathione reductase. It is possible that the inhibition of glutathione reductase by the B-chain may be of importance in regulating the amount of GSH available for the glutathione-insulin transhydrogenase reaction, thus providing a regulatory feed-back cycle.
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