1.9-A structures of ternary complexes of citrate synthase with D- and L-malate: mechanistic implications.

摘要: The structures of four isomorphous crystals ternary complexes chicken heart citrate synthase with D- or L-malate and acetyl coenzyme A carboxymethyl have been determined by X-ray crystallography fully refined at 1.9-A resolution. show that both D-malate bind in a very similar way the presence acetylCoA enzyme conformation is "closed". Hydrogen bond geometry suggested to account for difference binding constants two stereoisomers. suggest steric hindrance can observation proton exchange solvent catalyzed but not D-malate. malate reveal mode substrate ground state. carbonyl oxygen group hydrogen bonded water molecule histidine 274, allowing unambiguous identification orientation this group. support hypothesis transition-state analogue enolization step reaction (Bayer et al., 1981) additionally proposed mechanisms condensation (Karpusas 1990; Alter 1990).