The Biosynthesis of δ-Aminolevulinic Acid in Higher Plants: II. Formation of 14C-δ-Aminolevulinic Acid from Labeled Precursors in Greening Plant Tissues 1

TLDR: It appears probable that greening higher plant tissues possess an alternate route to δ-aminolevulinic acid in which the carbon skeleton of glutamate (and α-ketoglutarate) is incorporated intact into the first committed metabolite of the chlorophyll pathway.

Abstract: δ-Aminolevulinic acid was accumulated by greening cucumber ( Cucumis sativus L. var. Alpha green) cotyledons, barley ( Hordeum sativum var. Numar) leaves, and bean ( Phaseolus vulgaris L. var. Red Kidney) leaves in the presence of various 14 C-labeled precursors and levulinic acid, a competitive inhibitor of δ-aminolevulinic acid dehydrase. The radioactivity in the accumulated δ-aminolevulinic acid was measured. The most effective labeled precursors were the 5 carbon dicarboxylic compounds glutamate, glutamine, and α-ketoglutarate. 14 C-Labeled glycine and succinate were relatively poor. The carboxyl and the methylene carbons of glycine were incorporated into δ-aminolevulinic acid to about equal extent. The carboxyl carbon of glutamate was incorporated almost as well as the internal carbons of the same compound. These results are inconsistent with the succinyl CoA-glycine succinyl transferase (δ-aminolevulinic acid synthetase) mode of δ-aminolevulinic acid production. When the same experiments were performed on turkey blood (which, as avian blood in general, possesses δ-aminolevulinic acid synthetase), δ-aminolevulinic acid was labeled most effectively from glycine-2- 14 C, moderately well from glycine-1- 14 C and glutamate-3,4- 14 C and not at all from glutamate-1- 14 C. It appears probable that greening higher plant tissues possess an alternate route to δ-aminolevulinic acid in which the carbon skeleton of glutamate (and α-ketoglutarate) is incorporated intact into the first committed metabolite of the chlorophyll pathway.