Trout (Salmo gairdneri R.) liver 5-aminolevulinate synthetase: subcellular distribution and properties

The subcellular distribution of trout liver 5-aminolevulinate synthetase has been studied. A cytosolic form of the enzyme has been found. Its activity was a 30% of the mitochondrial enzyme. The cytosolic form has a molecular weight of 110,000, larger than the mitochondrial enzyme (70,000). The two enzyme forms showed a pH optimum of 7.5. The kinetic characteristic of both forms suggest that the cytosolic form is a precursor of the mitochondrial ALA-synthetase.