title: Relaxation studies of enzymes: rapid isomerization in deoxyribonuclease I.
abstract: Temperature-jump relaxation studies in deoxy-ribonuclease I were carried out at 10 degrees C and [I] = 0.1 M. The single observed relaxation time, which varied from 10(-4) to 10(-5) s, was characterized as a function of enzyme concentration, pH, and indicator concentration. The concentration and pH dependences of the relaxation time are in quantitative agreement with a mechanism involving an isomerization of the enzyme coupled to a rapid proton ionization process. The best fit forward and reverse isomerization rate constants are 6.5 X 10(3) and 7.2 X 10(4) s-1, respectively; the apparent pK is 5.7. The addition of urea brought about reductions in both the amplitude of the relaxation effect and the enzyme activity.
mesh_terms: D000818:Animals; D002417:Cattle; D003851:Deoxyribonucleases / Q000302:isolation & purification / Q000378:metabolism; D004720:Endonucleases / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D007700:Kinetics; D008433:Mathematics; D010179:Pancreas / Q000201:enzymology; D010664:Phenylmethylsulfonyl Fluoride
chemical_list: D010664:Phenylmethylsulfonyl Fluoride; D003851:Deoxyribonucleases; D004720:Endonucleases