Serine Biosynthesis in Rat Liver
REGULATION OF ENZYME CONCENTRATION BY DIETARY FACTORS
Harold J. Fallon 1, Edward J. Hackney 1, and William L. Byrne 1
From the
1 From the Departments of Medicine and Biochemistry, University of North Carolina School of Medicine, Chapel Hill, North Carolina, and the Department of Biochemistry, Duke University Medical Center, Durham, North Carolina
3-Phosphoglycerate dehydrogenase, phosphoserine phosphatase, d-glycerate dehydrogenase, and serine dehydratase have been measured in rats fet diets containing variable amounts of protein. Rats fed 2% casein diets for 7 days had a marked increase in 3-P-glycerate dehydrogenase and P-serine phosphatase and a simultaneous decline in serine dehydratase when compared to rats fed chow or a 25% casein diet. The increased enzyme levels were prevented by the addition of 1% cysteine to the 2% casein diet but this did not alter the decline in serine dehydratase. On 88% casein diets a depression of 3-P-glycerate dehydrogenase and P-serine phosphatase resulted, while prompt increase in serine dehydratase occurred. No reproducible changes in d-glycerate dehydrogenase occurred on any of the diets studied.
The administration of actinomycin D on several schedules consistently caused an inhibition of the changes noted with the 2% casein diet. These observations plus studies with cycloheximide suggest that the observed alterations in enzyme concentrations may be mediated by altered rates of enzyme synthesis.
Studies of potential feedback inhibitors of the reactions measured were negative for 3-P-glycerate dehydrogenase and d-glycerate dehydrogenase. Inhibition of P-serine phosphatase by l-serine may have physiological significance in mammals. The inhibition of serine dehydratase by l-cysteine is described.
Submitted on November 4, 1965
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