Metabolism of pent-4-enoate in rat heart. Reduction of the double bond

Abstract

1. Soluble extracts from rat heart and liver mitochondria were used to evaluate the early steps in the conversion of pent-4-enoyl-CoA into tricarboxylic acid-cycle intermediates. Hitherto the unresolved problem was the reduction of the double bond of pent-4-enoate. 2. Soluble extracts from heart mitochondria reduced pent-4-enoyl-CoA and penta-2,4-dienoyl-CoA in the presence of NADPH at rates (nmol/min per mg of protein) of 0.9 + 0.1 and 132 + 8 and from the liver mitochondria at the rates of 1.9 + 0.2 and 52 + 6 respectively. No reduction of acryloyl-CoA was found. 3. We show that primarily the double bond in position 4, not in position 2, of penta-2,4-dienoyl-CoA is reduced. 4. It is concluded that the principal metabolic pathway of penta-4-enoate is reduction of the double bond in position 4 after an initial oxidation to penta-2,4-dienoyl-CoA. The pent-2-enoyl-CoA thus formed can be further metabolized by the usual enzymes of f-oxidation, and by the further metabolism of propionyl-CoA to tricarboxylic acid-cycle intermediates.The hypoglycaemic agent pent-4-enoate inhibits fatty acid oxidation under many different kinds of conditions (e.g. Senior et al., 1968;Brendel et al., 1969;Fukami & Williamson, 1971). Pent-4-enoate itself can be slowly metabolized through #-oxidation, forming acetyl-CoA and acryloyl-CoA as end products (Brendel et al., 1969;, and the inhibition is apparently caused by some inhibitory intermediates during pent-4-enoate metabolism. We have shown, however, that in perfused rat hearts (Hiltunen, 1978) and in isolated heart mitochondria (Hiltunen et al., 1980) pent-4-enoate causes a rapid increase of tricarboxylic acid-cycle intermediates, and that pent-4-enoate itself is the source of these extra carbon skeletons. The mechanism seems to be that the C3 end products formed during the fl-oxidation of pent-4-enoate are metabolized via the propionate pathway into the tricarboxylic acid cycle.Reduction of the double bond is a prerequisite for the metabolism of pent-4-enoate by a mechanism suggested above. How and at which step of pent-4-enoate metabolism this takes place has remained unclear. We now show in experiments done with soluble extracts from heart and liver mitochondria and intermediates of pent-4-enoate metabolism that only the reduction of penta-2,4-dienoyl-CoA to pent-2-enoyl-CoA is rapid enough to account for the rate of pent-4-enoate metabolism found in perfused heart and liver.

Purification and characterization of 2-enoyl-CoA reductase from bovine liver

“…A possibility is the diminished capability to stabilize a partial positive charge at C-3, which should be required for the addition of the hydride ion from NADPH. The same observation has been made for another reaction involving a 2-trans-double bond: 2,4-dienoyl-CoA esters were reported to be very poor substrates for enoyl-CoA hydratases (Kunau et al, 1981;Hiltunen & Davis, 1981;Mizugaki et al, 1982b;Cuebas & Schulz, 1982;Dommes et al, 1983), which catalyse Table 3. Efiects of thiol reagents on 2-enoyl-CoA reductase The assay mixture (I ml) contained 2-enoyl-CoA reductase and 0.1 mM-NADPH in 50mM-potassium phosphate buffer, pH 7.4, containing 1 mM-EDTA and 1% bovine serum albumin.…”

The effects of 4-pentenoic and pentanoic acids on the isolated rat atria

“…Obviously, these rather striking findings cannot be satisfactorily explained on the basis of present data. However, it should be noted that 4-pentenoic acid can be P-oxidized through a pathway which proceeds separately from that involved in its inhibitory effects (HILTUNEN, 1978;HILTUNEN & DAVIS, 1981;BREMER, 1983). Hence, this catabolic route might compensate the shortage in the energy supply caused by the inhibition of the TG utilization.…”

The Effects of 4-Pentenoic and Pentanoic Acids on the Hypoxic Rat Atria

“…It should be noted, that 4-pentenoic acid can be &oxidized through a pathway different to that involved in its inhibitory properties (HILTUNEN, 1978;HILTUNEN & DAVIS, 1981;SCHULZ, 1987). Hence, possibly 4-pentenoic acid would be devoided of beneficial effects on hypoxia although it abolished the TG mobilization, because of the accumulation of its own oxidative metabolites.…”