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Effect of Dietary Protein and Vitamin B₆ on Hepatic Thionase Activity^1,2,

Four Figures

Department of Agricultural and Biological Chemistry, The Pennsylvania State College, State College

A study has been made of the effects of diets which varied in their content of casein or of thio amino acids and of pyridoxine on the hepatic thionase activity of growing rats. In addition, the hepatic thionase activity of rats which had been depleted of their vitamin B₆ reserve and subsequently fed pyridoxine has been determined. Furthermore, the effectiveness of pyridoxal phosphate in restoring thionase activity to liver extracts obtained from vitamin B₆-deprived rats was investigated. The results of these studies are summarized as follows:

1. Growing rats maintained on a breeding colony ration exhibited increasing hepatic thionase activity during the first three weeks of the experimental period, followed by a subsequent decrease in thionase activity.

2. Rats maintained on the semisynthetic diets supplemented with pyridoxine also showed increasing hepatic thionase activity during the experimental period following one week of adaptation to the regimen.

3. A marked and rapid decrease in hepatic thionase activity was observed in rats maintained on vitamin B₆-deficient diets. The addition of casein or thio amino acids to a vitamin B₆-deficient diet containing 20% casein resulted in a more rapid decrease of hepatic thionase activity.

4. Rats maintained on diets deficient in vitamin B₆ and containing 40% casein or added thio amino acids manifested vitamin B₆ deficiency symptoms in a much shorter period of time than did rats maintained on a 20% casein regimen.

5. Rats which were deprived of vitamin B₆ for 21 days showed a rapid restoration of hepatic thionase activity following pyridoxine supplementation.

6. The addition of pyridoxal phosphate to liver extracts obtained from vitamin B₆-deprived rats restored hepatic thionase activity.

² Data taken from a thesis presented by Robert Q. Thompson to the Graduate School of The Pennsylvania State College in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

³ Now affiliated with the Research Department, Parke, Davis and Company, Detroit, Michigan.

Manuscript received 12 February 1953.