β-Hydroxydecanoyl Thioester Dehydrase

Abstract

Abstract The enzyme β-hydroxydecanoyl thioester dehydrase, a requisite component of the fatty acid synthetase system of Escherichia coli, catalyzes the reversible interconversion of the thioesters of β-hydroxydecanoic acid, trans-α,β-decenoic acid, and cis-β, γ-decenoic acid. All activities of the dehydrase are strongly inhibited by 3-decynoyl-N-acetylcysteamine. A marked preference for C10 substrates has previously been noted. For further elucidation of dehydrase specificity, kinetic parameters for the enzymatic dehydration and isomerization were determined with a series of substrates varying in chain length from eight to 12 carbon atoms in the acyl moiety. Inhibition constants for β,γ-acetylenic thioesters of the same series were also measured. The data show a remarkable parallelism between the relative activities of substrates and inhibitors as a function of carbon chain length. The inhibitor 3-decynoyl-N-acetylcysteamine appears to be irreversibly bound to the dehydrase.