[Study of the enzymatic hydrolysis of a phosphonic ester using microcalorimetry].
A "Batch" microcalorimeter is used at 30 degrees C for the study of the hydrolysis of 4-nitro-phenylphenylphosphonate with a calf-intestinal phosphonate esterase, in a tris buffer, pH 8. The yield of enzymatic hydrolysis is estimated by spectrophotometric determination of the p--nitrophenol evolved; we have then calculated the apparent molar enthalph of the reaction. (delta Happ = -72,2 kj. mol-1). Phenylphosphonic acid, the second reaction product, is not transphosphonylated on tris. The second acidity of phenylphosphonic acid was studied at 30 degrees C by sodium hydroxide electrotitration (pKa2 = 7,13) and by "Flow" microcalorimetry (delta Hionization = 19,8 kj.mol-1). In the same manner at 30 degrees C, we measured the heat of ionization of p-nitrophenol (delta Hionization = 26,75 kj.mol-1). These findings allow a calculation for the actual heat of hydrolysis of 4-nitro-phenyl-phenylphosphonate (delta Hrho = -29,7 kj.mol-1).
D000818:Animals; D002151:Calorimetry / Q000379:methods; D002417:Cattle; D002854:Chromatography, Paper; D006868:Hydrolysis; D066298:In Vitro Techniques; D009596:Nitrophenols / Q000032:analysis / Q000378:metabolism*; D009943:Organophosphorus Compounds / Q000032:analysis / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000494:pharmacology*; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics
D009596:Nitrophenols; D009943:Organophosphorus Compounds; C023602:O-4-nitrophenyl phenylphosphonate; C023604:phenylphosphonic acid; D010744:Phosphoric Monoester Hydrolases; C023603:phosphonate esterase
Etude de l'hydrolyse enzymatique d'un ester phosphonique par microcalorimétrie.