title: Kinetic studies on the esterase activity of cytoplasmic sheep liver aldehyde dehydrogenase.
abstract: The hydrolysis of 4-nitrophenyl acetate catalysed by cytoplasmic aldehyde dehydrogenase (EC 1.2.1.3) from sheep liver was studied by steady-state and transient kinetic techniques. NAD+ and NADH stimulated the steady-state rate of ester hydrolysis at concentrations expected on the basis of their Michaelis constants from the dehydrogenase reaction. At higher concentrations of the coenzymes, both NAD+ and NADH inhibited the reaction competitively with respect to 4-nitrophenyl acetate, with inhibition constants of 104 and 197 micron respectively. Propionaldehyde and chloral hydrate are competitive inhibitors of the esterase reaction. A burst in the production of 4-nitrophenoxide ion was observed, with a rate constant of 12 +/- 2s-1 and a burst amplitude that was 30% of that expected on the basis of the known NADH-binding site concentration. The rate-limiting step for the esterase reaction occurs after the formation of 4-nitrophenoxide ion. Arguments are presented for the existence of distinct ester- and aldehyde-binding sites.
mesh_terms: D000085:Acetates / Q000378:metabolism; D000445:Aldehyde Oxidoreductases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000447:Aldehydes / Q000494:pharmacology; D000818:Animals; D002697:Chloral Hydrate / Q000494:pharmacology; D003593:Cytoplasm / Q000201:enzymology; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D009596:Nitrophenols / Q000378:metabolism*; D012756:Sheep
chemical_list: D000085:Acetates; D000447:Aldehydes; D009596:Nitrophenols; D009243:NAD; D002697:Chloral Hydrate; C008642:4-nitrophenyl acetate; D000445:Aldehyde Oxidoreductases