tailieunhanh - Báo cáo khoa học: On the thermodynamic equilibrium between (R)-2-hydroxyacyl-CoA and 2-enoyl-CoAOn the thermodynamic equilibrium between (R)-2-hydroxyacyl-CoA and 2-enoyl-CoA

A combined experimental and computational approach has been applied to investigate the equilibria between several a-hydroxyacyl-CoA compounds and their 2-enoyl-CoA derivatives. In contrast to those of theirb, candd counterparts, the equilibria for thea-compounds are relatively poorly char-acterized, but qualitatively they appear to be unusually sensitive to substit-uents. | On the thermodynamic equilibrium between R -2-hydroxyacyl-CoA and 2-enoyl-CoA Anutthaman Parthasarathy1 Wolfgang Buckel1 and David M. Smith2 1 Laboratory for Microbiology Philipps-Universitat Marburg Germany 2 Centre for ComputationalSolutions in the Life Sciences Rudjer Boskovic Institute Zagreb Croatia Keywords ab initio calculations enzymes kinetics solvent effects substituent effects Correspondence D. M. Smith Centre for Computational Solutions in the Life Sciences Rudjer Boskovic Institute Bijenicka 54 10000 Zagreb Croatia FaX 385 1 456 1182 Tel 385 1 456 1182 E-mail Received 20 December 2009 revised 25 January 2010 accepted 28 January 2010 A combined experimental and computational approach has been applied to investigate the equilibria between several a-hydroxyacyl-CoA compounds and their 2-enoyl-CoA derivatives. In contrast to those of their b y and Ỗ counterparts the equilibria for the a-compounds are relatively poorly characterized but qualitatively they appear to be unusually sensitive to substituents. Using a variety of techniques we have succeeded in measuring the equilibrium constants for the reactions beginning from 2-hydroxyglutaryl-CoA and lactyl-CoA. A complementary computational evaluation of the equilibrium constants shows quantitative agreement with the measured values. By examining the computational results we arrive at an explanation of the substituent sensitivity and provide a prediction for the as yet unmeasured equilibrium involving 2-hydroxyisocaproyl-CoA. doi Introduction Dehydratases catalyze a b-eliminations of water from hydroxy compounds and form a large class of enzymes over 100 different types are listed in the enzyme nomenclature database EC . In most cases the hydroxyl group is located in the b-position of an adjacent carboxylate CoA-thioester or ketone and the a-proton to be removed is thus activated. In a-amino acid fermentation pathways however dehydratases are found .