pH dependence of the redox potential of Pseudomonas aeruginosa cytochrome c-551

Electrostatic effects in proteins: comparison of dielectric and charge models

“…The effective value of e corresponding to the observed shift in cytochrome c55J is 27.4 (Moore et al, 1980). Moreover, the interactions involve charged sites which are well buried in the protein interior; thus surface effects which might be operative for interacting charges located near the protein surface are not present here.…”

“…In cytochrome c55J the situation is different since the charges are in the protein interior. The observed insensitivity of the shift in the redox potential to changes in ionic strength (Moore et al, 1980) shows that in the present case ionic screening does not affect the electrostatic interactions in the interior of the protein and for the SCP calculations we have taken 1=0. The pA" and redox shifts were calculated with both e wds and e,, since the latter may prove to be more appropriate in the present case (Mehler and Eichele, 1984).…”

“…The two propionic groups attached to the haem are buried at least 5 A beneath the protein's surface, and in the pH range 5-9 one of them is ionized, causing a shift in the redox potential of 65 mV (Moore, 1983) which appears to be independent of ionic strength [measurements were carried out at / =0.007 and 0.1 M and both ionic strengths yielded similar results (Moore et al, 1980)]. The pK 3 of the titrated propionate changes from a value of 7.3 in the reduced form to 6.2 in the oxidized state (Moore et al, 1980;Moore, 1983).…”

“…The two propionic groups attached to the haem are buried at least 5 A beneath the protein's surface, and in the pH range 5-9 one of them is ionized, causing a shift in the redox potential of 65 mV (Moore, 1983) which appears to be independent of ionic strength [measurements were carried out at / =0.007 and 0.1 M and both ionic strengths yielded similar results (Moore et al, 1980)]. The pK 3 of the titrated propionate changes from a value of 7.3 in the reduced form to 6.2 in the oxidized state (Moore et al, 1980;Moore, 1983). In addition, the conformation of the protein seems to be fairly stable to the ionization and to changes in electrostatic interactions generally, as can be seen from the similarity of the oxidized and reduced X-ray structures (Moore et al, 1980;Matsuura et al, 1982).…”

“…The pK 3 of the titrated propionate changes from a value of 7.3 in the reduced form to 6.2 in the oxidized state (Moore et al, 1980;Moore, 1983). In addition, the conformation of the protein seems to be fairly stable to the ionization and to changes in electrostatic interactions generally, as can be seen from the similarity of the oxidized and reduced X-ray structures (Moore et al, 1980;Matsuura et al, 1982).…”