Sj. Sadeghi et al., Ionic strength dependence of the non-physiological electron transfer between flavodoxin and cytochrome c(553) from D-vulgaris, J BIOL I CH, 5(6), 2000, pp. 730-737
A hypothetical model for the non-physiological electron transfer complex be
tween cytochrome c(553) (c(553)) and the flavodoxin (fld) from the sulphate
-reducing bacteria Desulfovibrio vulgaris has been recently published [1] b
ased on rigid-body docking and refined by molecular dynamics. In this study
, the functional validity of this model is tested by looking at the role of
electrostatics in the non-physiological interprotein electron transfer bet
ween the two proteins at different ionic strengths. The results are compare
d with the electron transfer between fld and cytochrome c fi-om horse heart
(hhc), Second-order rate constants (k(2)) were measured for both non-physi
ological systems at different ionic strengths: a complex, bell-shaped behav
iour is observed for the k(2) of the c(553)/fld redox pair with an optimum
rate at I=58 mmol l(-1), whereas under the same conditions the k(2) for hhc
/fld decreased monotonically with increasing ionic strength. Results from t
he electron transfer kinetics are rationalised in terms of reorganisational
effects of an ensemble of conformations of the electron transfer competent
c(553)/fld complexes, consistent with the published model.