Rapid mixing of ferrocytochrome c peroxi- sition (15). Corroboration of this rate by a more direct measurement is desirable in the context of understanding biological electron transfer rates.We, therefore, wish to report the direct measurement of electron transfer from cyt c peroxidase(II) to cyt c(III) within the cyt c(III)-cyt c peroxidase(II) complex. In addition, we report data for electron transfer in the derivative system, cyt c peroxidase-porphyrin (Por) cyt c7 (AP0 1 V), where Por-cyt c7 is the anion radical of Por-cyt c. Por-cyt c is iron-free cyt c. These systems together provide unique data on the dependence of protein electron transfer rates on AG.Finally, Ho et al. (16) reported an interesting study on the rate of oxidative quenching of the Zn-cyt c peroxidase triplet by cyt c(III). They found that 3kq depends markedly on the primary structure of the cytochrome with 3kq (yeast C) > 10 3kq (horse C). With the methods in hand to study a simple Fe(II)/Fe(III) redox reaction in the cyt c/cyt c peroxidase system, we report a comparative study of how the cyt c peroxidase(II) + cyt c(III) reaction depends on the primary structure of cyt c. (18). The product was purified by G-200 Abbreviations: cyt c, cytochrome c; Por, porphyrin. 1To whom reprint requests should be addressed.
MATERIALS AND METHODS
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