Effects of X-Ray Irradiation on Tryptophan Pyrrolase Induction In Vivo and In Vitro

Effects of whole body x-ray irradiation on the induction of tryptophan pyrrolase by tryptophan administration and also on the in vitro increment of tryptophan pyrrolase activity in rat liver homogenate incubated in tryptophan-containing complex medium were studied. 900 r of x-ray irradiation caused the increase in the substrate induced enzyme activity immediately as well as at 72 hours after exposure. The pattern of induction and decay course of tryptophan pyrrolase after tryptophan treatment, however, was not appreciably altered by x-ray irradiation. On the other hand, in vitro increments of tryptophan pyrrolase activity relative to original activity were significantly reduced in liver homogenate from x-ray irradiated rats, and this reduction in the in vitro inducibility by substrate addition in irradiated rat's liver homogenate was not prevented by prior treatment of irradiated animals with tryptophan. Possible roles of hormonal influences on the increased in vivo tryptophan pyrrolase induction after exposure and mitochondrial damage by x-ray irradiation relevent to the reduced in vitro inducibility are discussed. Acknowledgement-The author would like to thank Dr.keun-Bai Lee,professorof Biochemistry, and Dr. Min Wha Lee, Instructor of Biochemistry, Chonnam University Medical School, for advices and instructions. He is also indebted to De. Chi Yul Ahn, professor of X-ray, Catholic University Medical School and to Dr.DongJoon Kim, professor of Physiology, Ewha Woman's University Medical School, for their help performing of this investigation.