Mitochondrial pantetheinephosphate adenylyltransferase and dephospho-CoA kinase.

Abstract

Pantetheinephosphate adenylyltransferase and dephospho‐CoA kinase, which are last in the sequence leading to the biosynthesis of CoA, are localized in mitochondria (about 30% of the activity in the cell) and cytosol. The first three enzymes in the pathway are only found in cytosol [Skrede, S. and Halvorsen, O. (1979) Biochem. Biophys. Res. Commun. 91, 1536–1542]. Both enzymes are present in the mitochondrial matrix, but dephospho‐CoA kinase also has a more ‘external’ pool and is less easily removed from the membrane fractions of the mitochondria. In accordance with the submitochondrial fractionation studies, pantetheinephosphate adenylyltransferase is to a larger extent activated by detergents or mechanical disruption of the mitochondria than is dephospho‐CoA kinase. In intact mitochondria, the biosynthesis of CoA from 4‐phosphopantetheine was stimulated by uncoupling agents, probably because of facilitated penetration of the substrate through the inner mitochondrial membrane and or of leakage of a regulator. Intact mitochondria could increase the synthesis of CoA 5–10 times, when conditions were chosen to promote biosynthesis from 4‐phosphopantetheine and to remove CoA by acylation and/or ‘leakage’ out of the mitochondria. The kinetic properties of both mitochondrial enzymes are quite similar to the cytosolic ones (but our reinvestigation of the latter enzymes only partially confirm previous studies). Km for 4‐phosphopantetheine and dephosplio‐CoA were 0.015 and 0.01 mmol/1, respectively, for the mitochondrial enzymes. Mitochondrial biosynthesis of CoA was strongly inhibited by dephospho‐CoA at the pantetheinephosphate adenylyltransferase level and more slightly by CoA at the dephospho‐CoA kinase level