|Title||In vitro analysis of the chain termination reaction in the synthesis of poly-(R)-beta-hydroxybutyrate by the class III synthase from Allochromatium vinosum.|
|Publication Type||Journal Article|
|Year of Publication||2005|
|Authors||Lawrence, AG, Choi, J, Rha, CK, Stubbe, J, Sinskey, AJ|
|Date Published||2005 Jul-Aug|
|Keywords||Acyltransferases, Chromatiaceae, Escherichia coli, Hydroxybutyrates, Magnetic Resonance Spectroscopy, Molecular Weight, Polyesters|
Allochromatium vinosum polyhydroxyalkanoate synthase catalyzes formation of poly-(R)-3-hydroxybutyrate (PHB) from (R)-3-hydroxybutyryl-coenzyme A (HB-CoA). (R)-3-Hydroxybutyryl-N-acetylcysteamine (HB-NAC) is an alternative substrate for this synthase in vitro, with a turnover 1% that of HB-CoA. With HB-NAC, the molecular weight (M(w)) of PHB produced at substrate-to-enzyme ratios of 1500-15 000 is approximately 75 kDa. (1)H NMR shows that PHB produced has hydroxybutyrate at the alcohol end and N-acetylcysteamine (NAC) at the carboxylate end of the polymer. Exogenous NAC has no effect on the M(w) of PHB produced with HB-CoA or HB-NAC in vitro, whereas PHB from a polymerization reaction with both HB-CoA and HB-NAC has intermediate M(w). These results can be accommodated by two models. In the first, NAC liberated at the active site during polymerization acts as a chain transfer agent. In the second, there is a noncovalent polymer intermediate covalently linked to NAC, which can dissociate from the active site.
|Grant List||49171 / / PHS HHS / United States|