delta-Aminolevulinic acid synthase from Euglena gracilis.

delta-Aminolevulinic acid (ALA) synthase [succinyl-CoA:glycine C-succinyltransferase (decarboxylating), EC 2.3.1.37] activity was detected in cell extracts of the unicellular green flagellate alga Euglena gracilis. The enzyme was identified by substrate and cofactor requirements, and activity was proportional to number of cells extracted and duration of incubation. The incubation product was spectrophotometrically and chromatographically identical to ALA. ALA synthase activity is present in two wild-type strains, Z and bacillaris, and in nongreening, aplastidic strains derived from them. When grown in the dark, wild-type strains have amounts of ALA synthase activity equal to the amounts in their aplastidic derivative strains. Growth in the light or dark does not affect the level of ALA synthase activity in the aplastidic strains, but the wild-type strains have only one-third as much activity when grown in the light. We propose that ALA synthase is responsible for nonplastid tetrapyrrole biosynthesis in Euglena.