Purification and Properties of Solubilized Mitochondrial δ-Aminolevulinic Acid Synthetase and Comparison with the Cytosol Enzyme

Abstract

Abstract δ-Aminolevulinic acid synthetase extracted from porphyric liver mitochondria by sonication or freeze-drying was found to be excluded from Sephadex G-200, and other studies revealed that activity was associated with a large aggregate. In contrast, aminoacetone synthetase behaved as a soluble enzyme with a molecular weight of 64,000. By treating the aggregate with both sodium chloride and dithioerythritol, δ-aminolevulinic acid synthetase activity was released to yield a soluble form of enzyme of molecular weight 77,000, as determined by Sephadex gel chromatography. This form of the enzyme was purified 40-fold from rat liver mitochondria by a method involving affinity chromatography. Antibodies prepared against the purified mitochondrial enzyme cross-react with the cytosol enzyme, although Sephadex chromatography indicates its molecular weight to be 178,000. No enzymically inactive, immunologically reactive precursor of δ-aminolevulinic acid synthetase could be detected in normal rat liver. End product inhibition by hemin was found to be 50% at 10 µm.