Synthesis of Δ-aminolevulinic acid and chlorophyll by isolated chloroplasts

Abstract

Plastids isolated from immature spinach and greening barley or maize leaves incorporate L-glutamate-14C or α-ketoglutarate-14C into δ-aminolevulinate in the presence of levulinate. In its absence barley plastids incorporated L-glutamate-14C into chlorophylla. Optimal incorporation of label was obtained with plastids isolated and incubated in glycerol containing media. The half-life of the δ-aminolevulinate forming activity of the plastids was 5 min at 22°C and 1 hour at 0°C. In these plastid preparations δ-aminolevulinate synthesis is stimulated by light, ATP and aerobic conditions. Experiments employing photosynthetic inhibitors and artificial electron donors indicate the light stimulation to be indirect by provision of ATP and reducing power. Aminooxyacetate, DL-β-hydroxyglutamate and glyoxylate inhibited the synthesis of δ-aminolevulinate. In precursor competition experiments with α-ketoglutarate, L-glutamate is preferentially incorporated into δ-aminolevulinate. The plastids formed nmolar quantities of chemically identifiable δ-aminolevulinate.