title: Inactivation kinetics of dihydrofolate reductase from Chinese hamster during urea denaturation.
abstract: The kinetic theory of substrate reaction during modification of enzyme activity has been applied to the study of inactivation kinetics of Chinese hamster dihydrofolate reductase by urea [Tsou (1988) Adv. Enzymol. Relat. Areas Mol. Biol. 61, 381-436]. On the basis of the kinetic equation of substrate reaction in the presence of urea, all microscopic kinetic constants for the free enzyme and enzyme-substrate binary and ternary complexes have been determined. The results of the present study indicate that the denaturation of dihydrofolate reductase by urea follows single-phase kinetics, and changes in enzyme activity and tertiary structure proceed simultaneously in the unfolding process. Both substrates, NADPH and 7,8-dihydrofolate, protect dihydrofolate reductase against inactivation, and enzyme-substrate complexes lose their activity less rapidly than the free enzyme.
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Academia Sinica, Beijing 100101, China.
authors.forename: J W
authors.initials: JW
authors.lastname: Wu
authors.forename: Z X
authors.initials: ZX
authors.lastname: Wang
authors.forename: J M
authors.initials: JM
authors.lastname: Zhou
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D005470:Fluorometry; D005492:Folic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D007700:Kinetics; D046911:Macromolecular Substances; D009249:NADP / Q000494:pharmacology; D011489:Protein Denaturation; D017510:Protein Folding; D011993:Recombinant Fusion Proteins / Q000037:antagonists & inhibitors* / Q000187:drug effects; D013762:Tetrahydrofolate Dehydrogenase / Q000187:drug effects*; D014508:Urea / Q000494:pharmacology*
chemical_list: D046911:Macromolecular Substances; D011993:Recombinant Fusion Proteins; C010920:dihydrofolate; D009249:NADP; D014508:Urea; D005492:Folic Acid; D013762:Tetrahydrofolate Dehydrogenase