title: Interaction of acyl coenzyme A substrates and analogues with pig kidney medium-chain acyl-coA dehydrogenase.
abstract: Several alkylthio coenzyme A (CoA) derivatives (from ethyl- to hexadecyl-SCoA) have been synthesized to probe the substrate binding site in the flavoprotein medium-chain acyl-CoA dehydrogenase from pig kidney. All bind to apparently equivalent sites with a stoichiometry of four per tetramer. A plot of log Kd vs: hydrocarbon chain length is linear from 2 to 16 carbons with a free energy of binding of 390 cal/methylene group. These data suggest an acyl-binding site of moderate hydrophobicity and imply that the observed substrate specificity of the medium-chain dehydrogenase is not achieved simply by the length of the hydrocarbon binding pocket. Extrapolation of the graph to zero chain length predicts a Kd of 1 mM for the CoA moiety. The difference between this value and the experimentally determined value of 206 microM may be attributed to a contribution from the ionization of the sulfhydryl group in CoASH. The interaction of several eight-carbon intermediates of beta-oxidation (trans-2- and trans-3-octenoyl-CoA and L-3-hydroxy- and 3-ketooctanoyl-CoA) with the dehydrogenase has also been studied. All but the L-3-OH derivative bind tightly to the enzyme (with Kd values in the 50-90 nM range) and are very effective inhibitors of the dehydrogenation of octanoyl-CoA. The trans-3-enoyl analogue produces an immediate, intense, long-wavelength band (lambda max = 820 nm), which probably represents a charge-transfer interaction between the delocalized alpha-carbanion donor and oxidized flavin as the acceptor. The L-3-OH analogue is a reductant of the flavin, yielding 3-ketooctanoyl-CoA.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000214:Acyl Coenzyme A / Q000138:chemical synthesis / Q000378:metabolism* / Q000494:pharmacology; D042964:Acyl-CoA Dehydrogenase; D044944:Acyl-CoA Dehydrogenases / Q000378:metabolism*; D000818:Animals; D007668:Kidney / Q000201:enzymology*; D007700:Kinetics; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D013552:Swine
chemical_list: D000214:Acyl Coenzyme A; D044944:Acyl-CoA Dehydrogenases; D042964:Acyl-CoA Dehydrogenase