The role of succinyl-CoA synthetase in the control of heme biosynthesis

Abstract

1. 1. To study metabolic control of the pathway, accelerated porphyrin and heme biosynthesis in mouse liver was caused by the administration of either 2-allyl-2-isopropylacetamide or 3,5-dicarbethoxy-1, 4-dihydrocollidine to the intact animal. 2. 2. 4–6 h after a compound was administered, δ-aminolevulinate synthesis in liver mitochondria was increased eight-fold; the synthesis required addition of greater amounts of pyridoxal phosphate, magnesium, and phosphate to the medium, but 2-ketoglutarate was inhibitory. Results of experiments in vivo with 14C-labelled heme precursors suggested a larger succinate plus succinyl-CoA pool and an increased conversion of succinate to succinyl-CoA, with no change in tricarboxylic acid cycle turnover. The rate of succinyl-CoA hydrolysis by liver mitochondria remained unchanged in treated animals. 3. 3. Total succinyl-CoA synthetase (EC 6.2.1.4) activity in mitochondria increased about 70% within 2 h. Heat inactivation characteristics, pH responses, and electrophoretic separation of two enzyme activities showed the presence of a separate, inducible form of succinyl-CoA synthetase in liver mitochondria; puromycin prevented the enzyme induction. The inducible fraction of the enzyme was increased 300% in activity while the consititutive enzyme remained unchanged. 4. 4. The results are interpreted as indicating that succinyl-CoA synthetase is directly concerned with the metabolic control of the heme biosynthetic pathway in mouse liver cells.