Cytochrome c2 (cyt c2) is a protein found mainly in purple, non-sulfur, non-photosynthetic bacteria and is structurally similar to eukaryotic c-type cytochromes. The physio-chemical properties of cyt c2 are greatly influenced by pH and probing these effects is significant for understanding the electron transfer and proton transfer in the Electron Transport Chain. In this study, we investigate the reduction potential of the cytochrome c2 from Rhodospirillum rubrum and its mutant H42F across a range of pH values. By mutating the histidine at position 42 to a phenylalanine, we are altering a side chain that hydrogen bonds with the propionate of the heme group. When looking at the titration curves of the WT and H42F, we see that the WT protein at a low pH has a higher potential (370mV vs SHE) than the mutant (320mV). The potentials of both decrease as pH is increased, but the difference between potentials narrows at higher pH, going from 50 mV at pH 5 to 16 mV at pH 9. Thus, the titration curve for H42F is much less steep than the titration curve for WT. By removing this ionizable histidine, the reduction potential of the mutant is both lower and less affected by a change in pH. These findings support the possibility that His 42 can facilitate proton exchange upon oxidation and reduction of the protein.

Effect of pH on the reduction potential of cytochrome c2 and its H42F mutant

2019 Spring National Meeting

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