The Effect of X-irradiation on the Activation and Induction of Rat Liver Tryptophan Pyrrolase by Substrate and Hormone

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The 500R whole body X-irradiation inhibited the increase in holotryptophan pyrrolase activity which were induced by the single administration of cortisone or L-tryptophan in the adrenalectomized rats. However, no inhibitory effect of X-irradiation was found in the activity of holo-tryptophan pyrrolase which was induced by the combined administration of cortisone and L-tryptophan. It was suggested that the radiation effect on holo-tryptophan pyrrolase formation in the cortisone induction was the result of inhibited conversion of apo-tryptophan pyrrolase to holo-tryptophan pyrrolase, whereas apo-tryptophan pyrrolase formation was scarcely affected by X-irradiation. On the other hand, in the tryptophan-induction an inhibition occurred in other processes, presumably in apo-tryptophan pyrrolase formation. The mechanism underlying the elimination of inhibitory effects of X-irradiation under the coexistance of cortisone and tryptophan was discussed.
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