SOLUBLE HEPATIC δ-AMINOLEVULINIC ACID SYNTHETASE: END-PRODUCT INHIBITION OF THE PARTIALLY PURIFIED ENZYME

Abstract

The present study confirms the existence of hepatic delta-aminolevulinic acid synthetase in the cytosol of the liver, suggests that this enzyme may be in transit to the mitochondria, and defines some of the characteristics of the partially purified enzyme. The substrate and cofactor requirements are similar to those of mitochondrial delta-aminolevulinic acid synthetase. Heme strongly inhibits the partially purified enzyme. A number of proteins that bind heme block this inhibition, which explains previous failures to demonstrate heme inhibition in crude systems. End-product inhibition of delta-aminolevulinic acid synthetase in the mitochondria may play an important role in the regulation of heme biosynthesis in eukaryotic cells.