Effect of various concentrations of protein in chick diet upon the metabolic enzymes of glycine and serine.

The effect of feeding low protein diets with and without 2% glycine or 2% L-serine to chicks upon the enzymes concerned in the matabolism of glycine and serine has been determined. D-3-phosphoglycerate dehydrogenase (EC 1.1.1.s), hosphoserine phosphatase (EC 3.1.3.3), and serine hydroxymethyltransferase (EC 2.1.2.1) activities were significantly increased in livers from chicks fed 75% protein diets as compared to liver enzyme activities from chicks fed either 24% chick starter, 2% or 25% protein diets. Phosphoserine phosphatase activity was significantly higher in kidney tissue of chicks fed 75% protein diets. Livers from chicks fed 25% protein diets had a higher activity for D-3-phosphoglycerate dehydrogenase and phosphoserine phosphatase than did those fed chick starter or 2% protein diets. D-3-phosphoglycerate dehydrogenase and phosphoserine phosphatase activities were higher in livers from chicks fed 2% protein, 2% protein + 2% glycine, and 2% protein + 2% L-serine diets when compared to those from chicks fed low protein diets with supplemental methionine or cysteine. Serine dehydratase (EC 4.2.1.13), glycerate dehydrogenase (EC 1.1.1.29) and hydroxypyruvate-P: L-glutamate transaminase activities remained constant in livers from chicks fed all experimental diets. The uric acid concentration was significantly increased in plasma from chicks fed the high protein diets which suggests that D-3-phosphoglycerate dehydrogenase, phosphoserine phosphatase and serine hydroxymethyltransferase activities were increased because of the high requirement for glycine in uric acid formation. The 75% protein diet provided three times as much glycine as the 25% protein diet which may have met the increased need for glycine for uric acid formation.