title: Enthalpy and enzyme activity of modified histidine residues of adenosine deaminase and diethyl pyrocarbonate complexes.
abstract: Kinetic and thermodynamic studies have been made on the effect of diethyl pyrocarbonate as a histidine modifier on the active site of adenosine deaminase in 50 mM sodium phosphate buffer pH 6.8, at 27 degrees C using UV spectrophotometry and isothermal titration calorimetry (ITC). Inactivation of adenosine deaminase by diethyl pyrocarbonate is correlated with modification of histidyl residues. The number of modified histidine residues complexed to active site of adenosine deaminase are equivalent to 4. The number and energy of histidine binding sets are determined by enthalpy curve, which represents triple stages. These stages are composed of 3,1 and 1 sites of histidyl modified residues at diethyl pyrocarbonate concentrations, 0.63, 1.8, 3.3 mM. The heat contents corresponding to the first, second and third sets are found to be 18000, 22000 and 21900 kJ mol(-1) respectively.
authors.affiliation: Institute of Biochemistry and Biophysics, University of Tehran, Tehran, Iran.
authors.forename: G
authors.initials: G
authors.lastname: Ataie
authors.forename: A A
authors.initials: AA
authors.lastname: Moosavi-Movahedi
authors.forename: A A
authors.initials: AA
authors.lastname: Saboury
authors.forename: G H
authors.initials: GH
authors.lastname: Hakimelahi
authors.forename: J R
authors.initials: JR
authors.lastname: Hwu
authors.forename: S C
authors.initials: SC
authors.lastname: Tsay
mesh_terms: D000243:Adenosine Deaminase / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D004047:Diethyl Pyrocarbonate / Q000378:metabolism*; D006639:Histidine / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet / Q000379:methods
chemical_list: D006639:Histidine; D000243:Adenosine Deaminase; D004047:Diethyl Pyrocarbonate