Biochemistry, Department of


Document Type


Date of this Version



J Physiol 562.2 (2005) pp 307–318


Copyright The Physiological Society 2004


5-Hydroxydecanoate (5-HD) blocks pharmacological and ischaemic preconditioning, and

has been postulated to be a specific inhibitor of mitochondrial ATP-sensitive K+ (KATP)

channels. However, recent work has shown that 5-HD is activated to 5-hydroxydecanoyl-CoA

(5-HD-CoA), which is a substrate for the first step of β-oxidation. We have now

analysed the complete β-oxidation of 5-HD-CoA using specially synthesised (and purified)

substrates and enzymes, as well as isolated rat liver and heart mitochondria, and compared

it with the metabolism of the physiological substrate decanoyl-CoA. At the second step of

β-oxidation, catalysed by enoyl-CoA hydratase, enzyme kinetics were similar using either

decenoyl-CoA or 5-hydroxydecenoyl-CoA as substrate. The last two steps were investigated

using l-3-hydroxyacyl-CoA dehydrogenase (HAD) coupled to 3-ketoacyl-CoA thiolase. Vmax

for the metabolite of 5-HD (3,5-dihydroxydecanoyl-CoA) was fivefold slower than for the

corresponding metabolite of decanoate (L-3-hydroxydecanoyl-CoA). The slower kinetics were

not due to accumulation of D-3-hydroxyoctanoyl-CoA since this enantiomer did not inhibit

HAD. Molecular modelling of HAD complexed with 3,5-dihydroxydecanoyl-CoA suggested

that the 5-hydroxyl group could decrease HAD turnover rate by interacting with critical

side chains. Consistent with the kinetic data, 5-hydroxydecanoyl-CoA alone acted as a

weak substrate in isolated mitochondria, whereas addition of 100 μM 5-HD-CoA inhibited

the metabolism of decanoyl-CoA or lauryl-carnitine. In conclusion, 5-HD is activated,

transported into mitochondria and metabolised via β-oxidation, albeit with rate-limiting

kinetics at the penultimate step. This creates a bottleneck for β-oxidation of fatty acids. The

complex metabolic effects of 5-HD invalidate the use of 5-HD as a blocker of mitochondrial

KATP channels in studies of preconditioning.