Inactivation kinetics of dihydrofolate reductase from Chinese hamster during urea denaturation.
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.
Wu
J W
JW
National Laboratory of Biomacromolecules, Institute of Biophysics, Academia Sinica, Beijing 100101, China.
Wang
Z X
ZX
Zhou
J M
JM
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*
D046911:Macromolecular Substances; D011993:Recombinant Fusion Proteins; C010920:dihydrofolate; D009249:NADP; D014508:Urea; D005492:Folic Acid; D013762:Tetrahydrofolate Dehydrogenase