Figure 20-13


CαCβ bond:
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A ribbon diagram of the active site region in a subunit of medium-chain acyl-CoA dehydrogenase from pig liver mitochondria in complex with octanoyl-CoA. The enzyme is a tetramer of identical 385-residue subunits, each of which binds an FAD prosthetic group (green) and an octanoyl-CoA substrate (whose octanoyl and CoA moieties are cyan and white) in largely extended conformations. The octanoyl-CoA binds such that its CαCβ bond is sandwiched between the carboxylate group of Glu 376 (red) and the flavin ring (green), consistent with the proposal that Glu 376 is the general base that abstracts the α proton in the α,β dehydrogenation reaction catalyzed by the enzyme. Click on the button labeled "Highlight CαCβ Bond" to thicken this bond of the substrate. [X-ray structure by Jung-Ja Kim, Medical College of Wisconsin. PDBid 3MDE.]