Abstract：
:Oxalate is the strongest known inhibitor of yeast cytochrome b2 activity. We have used spectrophotometric titration, temperature-jump relaxation, and calorimetry in an investigation of the interaction between enzyme and inhibitor. The titration data are consistent with noncooperative binding to one site per subunit. This conclusion is corroborated by temperature-jump results which reveal a single relaxation phenomenon which obeys second-order kinetics. Further evidence for a simple binding reaction enthalpy estimated from relaxation amplitudes is in good agreement with the value obtained directly with batch calorimetry. The forward and reverse rate constants evaluated from the temperature-jump experiments are, respectively, 1 x 10(4) M-1 sec-1 and 15 sec-1. Although considerably smaller than a diffusion-controlled value, the forward rate constant is characterized by an unusually small activation energy of approximately 3 kcal/mol. This, together with a large unfavorable association activation entropy of -30 eu, suggests that oxalate diffuses freely to the active site, but only a small fraction of the collisions are productive due to severe steric requirements.
journal_name
Biochemistryjournal_title
Biochemistryauthors
Thusius D,Blazy B,Baudras Adoi
10.1021/bi00647a002subject
Has Abstractpub_date
1976-01-27 00:00:00pages
250-6issue
2eissn
0006-2960issn
1520-4995journal_volume
15pub_type
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