Glycine decarboxylation in the porcine erythrocyte: Its relation to aminolevulinic acid synthesis

Abstract

1. 1. Available methods for measuring the rate of synthesis δ-aminolevulinic acid are not sufficiently sensitive for use with normal mammalian erythrocytes. Since glycine is decarboxylated in the course of δ-aminolevulinic acid synthesis, the rate of liberation of 14CO 2 from [I- 14C]glycine can be utilized as a sensitive measure of this reaction. Such a measure would be valid only if other pathways leading to glycine decarboxylation are not quantitavely significant in erythrocytes. For this reason, a study of the pathways leading to glycine decarboxylation in erythrocytes was made. 2. 2. Glycine decarboxylation in young erythrocytes was found to be inhibited by rans-aconitate, and the inhibition was partially reversed by α-ketoglutaric acid or succinate. 3. 3. At least 77% of α-ketoglutaric acid-dependent glycine decarboxylation was accounted for the synthesis of α-aminolevulinic acid. No evidence of other pathways of glycine decarboxylation in young erythrocytes was found. 4. 4. α-Ketoglutaric acid-dependent glycine decarboxylation was similar to the δ-aminolevulinic acid synthetase reaction in substrate-activity relationships, pH optima and the effects of inhibitors. 5. 5. Like δ-aminolevulinic acid synthesis, α-ketoglutaric acid-dependent glycine decarboxylation required an intact, sedimentable cell fraction and occured to a much greater extent in very young erythrocytes. 6. 6. Glycine was not converted to serine or glyoxylate in young erythrocytes. Glyoxylate was decarboxylated and the rate of decarboxylation was increased upon the addition of α-ketoglutaric acid. 7. 7. It is concluded that when appropriate conditions are selected, glycine decarboxylation in crythrocytes may be used as a measure of δ-aminolevulinic acid sythesis.