Inhibition of Glycine Oxidation in Cultured Fibroblasts by Isoleucine

Abstract

Extract: Cultured fibroblasts were shown to oxidize glycine to CO₂-Isoleucine (10 mM) inhibited glycine oxidation to CO₂ by about 60% in a concentration range of from 0.025 to 10 mM glycine in fibroblasts grown from a patient with β-ketothiolase deficienty. Glycine oxidation by control cell lines was not inhibited by isoleucine. These studies demonstrate an interrelation between isoleucine catabolism and glycine oxidation in fibroblasts cultured from a patient with the ketotic hyperglycinemia syndrome.

Speculation: Hyperglycinemia and hyperglycinuria seen in the “ketotic hyperglycinemia” syndrome would appear to be secondary to accumulation of products of isoleucine catabolism. Thus, the varying levels of glycine reported in the serum and urine of these patients probably reflect differences in protein and isoleucine intake than rather primary blocks in glycine metabolism.

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