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The Influence of High Glycine Diets on the Activity of Glycine-Catabolizing Enzymes and on Glycine Catabolism in Rats

Central Institute of Nutrition, Academy of Sciences of the German Democratic Republic, Arthur-Scheunert-Allee 114-116, 1505 Potsdam-Rehbruecke, German Democratic Republic

Male albino rats were adapted to isocaloric purified diets that differed mainly in their glycine and casein contents. Controls received a 30% casein diet. In experimental diets gelatin or gelatin hydrolysate was substituted for half of the 30% casein. An additional group was fed a glycine-supplemented diet, which corresponded in glycine level to the gelatin diet but in which the protein level was nearly the same as that of the casein control diet. Another group received a 15% casein diet. Rat liver glycine cleavage system, serine hydroxymethyltransferase and serine dehydratase activities were measured. ¹⁴CO₂ production from the catabolism of ¹⁴C-labeled glycine was measured in vivo and in vitro (from isolated hepatocytes). Serine dehydratase and glycine cleavage system activities were higher in animals fed 30% casein diets than in those fed 15% casein diets. Serine hydroxymethyltransferase activity of the cytosolic and mitochondrial fractions was highest when a high glycine diet (glycine administered as pure, protein bound in gelatin or peptide bound in gelatin hydrolysate) was fed. ¹⁴CO₂ formation from [1-¹⁴C]- and [2-¹⁴C]glycine both in vivo and in isolated hepatocytes was higher when a high glycine diet was fed than when a casein diet was fed. These results suggest that glycine catabolism is dependent on and adaptable to the glycine content of the diet. Serine hydroxymethyltransferase appears to play a major role in the regulation of glycine degradation via serine and pyruvate.

KEY WORDS: • glycine • catabolism • glycine cleavage system • serine hydroxymethyltransferase • serine dehydratase • liver

Manuscript received 4 February 1985. Revision accepted 23 December 1985.

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