Kinetics of the reduction of metalloproteins by chromous ion

Creators: Dawson, J. W.; Gray, H. B.; Holwerda, R. A.; Westhead, E. W.

Abstract

The reduction of Cu(330) in Rhus vernicifera laccase by chromous ion is 30% faster than reduction of Cu(614) at room temperature [pH 4.8, µ = 0.1 (NaCl)], and two parallel first-order paths, attributed to heterogeneity of the protein, are observed at both wavelengths. The reactions of stellacyanin, spinach and French-bean plastocyanins, and cytochrome c with chromous ion under similar conditions are faster than that with laccase by factors of 102 to 104, and are first order in protein concentration. Comparison of rates and activation parameters for the reduction of "blue" copper in laccase, stellacyanin, and the two plastocyanins indicates that reduction of the Cu(614) site in laccase may occur by intramolecular electron transfer from one of the Cu(330) sites. Our value of ΔH (17.4 kcal/mol) for the chromous ion reduction of cytochrome c is consistent with a mechanism in which major conformational changes in the protein must accompany electron transfer.

Additional Information

© 1972 by the National Academy of Sciences. Contributed by H. B. Gray, October 27, 1971. We thank J. M. Schredder and B. Dohner for technical assistance and Dr. R. E. Dickerson for useful discussions. Helpful comments on our manuscript were provided by Dr. L. Bennett. This work was supported by the National Science Foundation (H.B.G.), and in part by the USPHS grants GM 14945 and AM 11157 (E.W.W.). R.A.H. thanks the N.S.F. for a Graduate Fellowship (1970-71). This is contribution No. 4367 from the Arthur Amos Noyes Laboratory.

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