Biomaterial Database

Butyryl-CoA dehydrogenase from Megasphaera elsdenii. Specificity of the catalytic reaction. 1984

G Williamson, and P C Engel

The absorption coefficient of butyryl-CoA dehydrogenase from Megasphaera elsdenii at 450 nm is determined as 14.4 mM-1 X cm-1 in the CoA-free form and 14.2 mM-1 X cm-1 in the CoA-liganded form (both yellow). The latter value is considerably higher than the earlier published estimate. Phenazine ethosulphate offers great advantages over phenazine methosulphate as a coupling dye in the catalytic assay despite giving lower Vmax. values (506 min-1 as compared with 1250 min-1 under the conditions used). The phenazine ethosulphate assay is used to establish a pH optimum of 8.05 for oxidation of 100 microM-butyryl-CoA. The rates of oxidation of a range of straight-chain, branched-chain and alicyclic acyl thioesters are used to provide the following information. Only straight-chain acyl groups containing 4-6 carbon atoms are easily accommodated by the postulated hydrophobic pocket of the enzyme. C-3-substituted acyl-CoA thioesters are not oxidized at a significant rate, suggesting that the C-3 pro-S-hydrogen atom of straight-chain substrates is partially exposed to the solvent. Acyl-CoA thioesters with substitutions at C-2 are oxidized, though at a lower rate than their straight-chain counterparts. This implies that the C-2 pro-S-hydrogen atom of straight-chain substrates is partially exposed to the solvent. Saturated alicyclic carboxylic acyl-CoA thioesters with 4-7 carbon atoms in the ring are oxidized, with maximal activity for the cyclohexane derivative. This implies that optimal oxidation requires a true trans orientation of the two departing hydrogen atoms. The strain imposed by bound unsaturated alicyclic acyl thioesters strikingly perturbs the flavin visible-absorption spectrum, with the exception of the cyclohex-2-ene derivative, which forms a complex with similar spectral properties to those of the crotonyl-CoA complex. In the thiol moiety of thioester substrates the amide bond of N-acetylcysteamine is essential for both binding and catalysis. The adenosine structure contributes substantially to strong binding, but is less important in determining the catalytic rate.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D004579	Electron Transport	The process by which ELECTRONS are transported from a reduced substrate to molecular OXYGEN. (From Bennington, Saunders Dictionary and Encyclopedia of Laboratory Medicine and Technology, 1984, p270)	Respiratory Chain,Chain, Respiratory,Chains, Respiratory,Respiratory Chains,Transport, Electron
D006863	Hydrogen-Ion Concentration	The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH	pH,Concentration, Hydrogen-Ion,Concentrations, Hydrogen-Ion,Hydrogen Ion Concentration,Hydrogen-Ion Concentrations
D000214	Acyl Coenzyme A	S-Acyl coenzyme A. Fatty acid coenzyme A derivatives that are involved in the biosynthesis and oxidation of fatty acids as well as in ceramide formation.	Acyl CoA,Fatty Acyl CoA,Long-Chain Acyl CoA,Acyl CoA, Fatty,Acyl CoA, Long-Chain,CoA, Acyl,CoA, Fatty Acyl,CoA, Long-Chain Acyl,Coenzyme A, Acyl,Long Chain Acyl CoA
D001665	Binding Sites	The parts of a macromolecule that directly participate in its specific combination with another molecule.	Combining Site,Binding Site,Combining Sites,Site, Binding,Site, Combining,Sites, Binding,Sites, Combining
D013053	Spectrophotometry	The art or process of comparing photometrically the relative intensities of the light in different parts of the spectrum.
D013329	Structure-Activity Relationship	The relationship between the chemical structure of a compound and its biological or pharmacological activity. Compounds are often classed together because they have structural characteristics in common including shape, size, stereochemical arrangement, and distribution of functional groups.	Relationship, Structure-Activity,Relationships, Structure-Activity,Structure Activity Relationship,Structure-Activity Relationships
D013379	Substrate Specificity	A characteristic feature of enzyme activity in relation to the kind of substrate on which the enzyme or catalytic molecule reacts.	Specificities, Substrate,Specificity, Substrate,Substrate Specificities
D044926	Butyryl-CoA Dehydrogenase	A flavoprotein oxidoreductase that has specificity for short-chain fatty acids. It forms a complex with ELECTRON-TRANSFERRING FLAVOPROTEINS and conveys reducing equivalents to UBIQUINONE.	Butyryl Dehydrogenase,Butyryl-Coenzyme A Dehydrogenase,Short-Chain Acyl-CoA Dehydrogenase,Acyl-CoA Dehydrogenase, Short-Chain,Butyryl CoA Dehydrogenase,Butyryl Coenzyme A Dehydrogenase,Dehydrogenase, Butyryl,Dehydrogenase, Butyryl-CoA,Dehydrogenase, Butyryl-Coenzyme A,Dehydrogenase, Short-Chain Acyl-CoA,Short Chain Acyl CoA Dehydrogenase
D044943	Fatty Acid Desaturases	A family of enzymes that catalyze the stereoselective, regioselective, or chemoselective syn-dehydrogenation reactions. They function by a mechanism that is linked directly to reduction of molecular OXYGEN.	Acyl CoA Desaturase,Enoyl CoA Reductase,Fatty Acid Desaturase,Fatty Acid Desaturating Enzymes,Acyl CoA Desaturases,Enoyl CoA Reductases,Acid Desaturase, Fatty,CoA Desaturase, Acyl,CoA Reductase, Enoyl,Desaturase, Acyl CoA,Desaturase, Fatty Acid,Desaturases, Fatty Acid,Reductase, Enoyl CoA,Reductases, Enoyl CoA