Control of formation and dissociation of the high-affinity complex between cytochrome c and cytochrome c peroxidase by ionic strength and the low-affinity binding site

Biochemistry
H MeiF Millett

Abstract

A new ruthenium photoreduction technique was used to measure the formation and dissociation rate constants kf and kd of the high-affinity complex between yeast iso-1-cytochrome c (yCc) and cytochrome c peroxidase compound I (CMPI) over a wide range of ionic strength. These studies utilized Ru-39-Cc, which contains trisbipyridylruthenium attached to the cysteine residue in the H39C, C102T variant of yCc, and has the same reactivity with CMPI as native yCc. kd and kf were measured by photoreducing a small concentration of Ru-39-Cc in the presence of the oxidized yCcIII: CMPI complex, which must dissociate before Ru-39-CcII can bind to CMPI and reduce the radical action. The value of kd for the 1:1 high-affinity complex is very small at low ionic strength, < 5 s-1 but is increased significantly by binding yCc to a second low-affinity site. However, the low-affinity yCc binding site is not active in direct electron transfer to either the radical cation or the oxyferryl heme in CMPI, and is too weak to play a role in the kinetics at ionic strengths above 70 mM. The value of kd increases to 4000 s-1 at 150 mM ionic strength, while kf decreases from > 3 x 10(9) M-1 s-1 at low ionic strength to 1.3 x 10(9) M-1 s-1 at 150 mM ionic stren...Continue Reading

Citations

Jun 5, 2002·Biochimica Et Biophysica Acta·James E Erman, Lidia B Vitello
Dec 2, 1998·Journal of Biomolecular Structure & Dynamics·G CastroS H Northrup
Nov 21, 2014·Journal of the Royal Society, Interface·Marian BreuerJulea N Butt
Aug 9, 2011·Biochimica Et Biophysica Acta·Alexander N VolkovJonathan A R Worrall
May 7, 2015·Nature Communications·Karen Van de WaterAlexander N Volkov
Aug 12, 2014·Journal of Chemical Theory and Computation·Ozlem UlucanVolkhard Helms
Oct 12, 2019·Journal of the American Chemical Society·Estella F YeeBrian R Crane

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