Purification, Characterization, and Fractionation of the delta-Aminolevulinic Acid Synthesizing Enzymes from Light-Grown Chlamydomonas reinhardtii Cells

Abstract

The synthesis of delta-aminolevulinate from glutamate by Chlamydomonas reinhardtii membrane-free cell homogenates requires Mg(2+), ATP, and NADPH as cofactors. The pH optimum is about 8.3. When analyzed by a Fractogel TSK gel filtration column the delta-aminolevulinate synthesizing enzymes, including glutamate-1-semialdehyde aminotransferase, elute with an apparent molecular weight of about 45,000. The enzymes obtained from the gel filtration column were separated into three fractions by affinity column chromatography. One fraction binds to heme-Sepharose, one to Blue Sepharose, while the enzyme converting the putative glutamate-1-semialdehyde to delta-aminolevulinic acid is retained by neither column. All three fractions are necessary for the conversion of glutamate to delta-aminolevulinate. The delta-aminolevulinate synthesizing enzymes from Chlamydomonas are sensitive to inhibition by heme but not sensitive to inhibition by protoporphyrin.