Further Observations on Factors Affecting L-Cysteine Desulfhydrase Activity in Chick Liver

L-cysteine desulfhydrase activity in chick liver was reduced by feeding either a low-protein or a protein-free ration and was increased by feeding a high-protein ration rich in gelatin. Increasing the nitrogen levels of the ration by the addition of urea or ammonium citrate had little or no effect on the enzyme activity of chicks fed the rations. Intraperitoneal administration of L-cysteine or of L-histidine resulted in increased activity; DL-methionine, L-glutamic acid and L-arginine were not effective. The injection of cortisone or histamine resulted in an increase in cysteine desulfhydrase activity. The increased activity due to cortisone administration was prevented by simultaneous injection of vitamin B12. Stress resulting from restriction of water intake or fasting caused an increase in enzyme concentration. Intraperitoneal administration of dextrose during fasting arrested the increase. Feeding of thyroprotein resulted in a marked depression in cysteine desulfhydrase concentration, while inclusion of thiouracil in the ration increased activity of the enzyme.