Photoinduced electron-transfer reaction in a ternary system involving zinc cytochrome c and plastocyanin. Interplay of monopolar and dipolar electrostatic interactions between metalloproteins

Abstract

A carbodiimide promotes noninvasive cross-linking between amino groups surrounding the exposed heme edge in zinc cytochrome c and carboxylic groups in the acidic patch in plastocyanin. Eight derivatives of the covalent complex Zncyt/pc(I), which have similar structures but different overall charges because of different numbers and locations of N-acylurea groups, are separated by cation-exchange chromatography. Kinetics of electron transfer from the diprotein complex in the triplet excited state, 3Zncyt/pc(I), to free cupriplastocyanin at pH 7.0 and various ionic strengths is studied by laser flash spectroscopy. This reaction is purely bimolecular for all eight N-acylurea derivatives of the diprotein complex. The overall charges of the derivatives 1 and 2 at pH 7.0 are -2 and 0, respectively; both of them, however, have very large dipole moments of 410-480 D. The rate constants for their reactions with cupriplastocyanin, whose charge at pH 7.0 is -8 and whose dipole moment is 362 D, are determined over the range of ionic strengths from 2.5 mM to 3.00 M. The observed dependence of the rate constants on ionic strength cannot be explained in terms of net charges (monopole-monopole interactions) alone, but it can be fitted quantitatively with a theory that recognizes also monopole-dipole and dipole-dipole interactions [van Leeuwen, J. W. (1983) Biochim. Biophys. Acta 743, 408]. At ionic strengths up to ca. 10 mM monopole-monopole interactions predominate and Brønsted-Debye-Hückel theory applies.(ABSTRACT TRUNCATED AT 250 WORDS)

A “parallel plate” electrostatic model for bimolecular rate constants applied to electron transfer proteins

“…In the case of simple ionic strength dependencies, we have shown that the monopolar and dipolar contributions are not experimentally resolvable. Furthermore, in order to fit more complex ionic strength dependencies, which show an increase in rate constant followed by a decrease (or the opposite situation) with increasing ionic strength, it is necessary to have different signs for the monopolar and dipolar contributions, as was also reported by Zhou and Kostic (1992). Thus, the vj and vd terms are apparently distinguishable in these examples.…”

“…There are several examples of more complicated ionic strength dependencies for electron transfer protein reactions. These either show an increase in rate constant at low ionic strengths and then a decrease at higher ionic strengths (Hazzard et ai., 1988(Hazzard et ai., , 1991Walker et al, 1991;Zhou & Kostic, 1992;Hurley et al, 1993;Meyer et al, 1993bMeyer et al, , 1993cPan et al, 1993;Tollin et al, 1993), or the opposite dependence, i.e., a decrease followed by an increase in rate constant with increasing ionic strength (Cheddar et al, 1989). Such data are more difficult to analyze than are the simple cases, but can be fit with the parallel plate model using both monopolar and dipolar terms, as shown in Figure 5.…”

Evolving the [Myoglobin, Cytochromeb5] Complex from Dynamic toward Simple Docking: Charging the Electron Transfer Reactive Patch

“…One might expect that at relatively low values of − q Mb q b5 , where there has been little localized charge buildup, the electrostatic interactions would involve charges over a wide area, and not be so simply parametrizable. (48)(49, 50) …”

Transition Metals in Supramolecular Chemistry

“…The role of a protein dipolar moment has been previously indicated as a driving force for a favourable orientation during complex formation involving c-type cytochromes Tollin, 1985, Zhou andKostic, 1992]. In particular, in previous studies on the interaction of cytochrome C3 with several redox partners, a consistent emphasis has been given to the possible stabilisation of the complexes due to the formation salt bridges between the positively charged residues that surrounds one of the four hemes, and acidic residues on the interacting protein [Cambillau et al, 1988, Stewart et al, 1988.…”

“…A significant effort has been put on the study and characterisation of the nature and properties of several electron transfer complexes: cytochrome c and cytochrome bS [Salemme et al, 1976;Stonehuemer et al, 1979;Mauk et al, 1982;Eley and Moore, 1983;Wendoloski et al, 1987;Burch et al, 1990;Whitford et al, 1990;Eltis et al, 1991;Willie et al, 1992], cytochrome c with cytochrome c peroxidase [Poulos and Kraut, 1980;Pelletier and Kraut, 1992], cytochrome c with flavodoxin [Simondsen et al, 1982;Simondsen and Tollin, 1983;Tollin et al, 1984;Weber and Tollin, 1985;Dickerson et al, 1985;Hazzard et al, 1986;Tollin et al, 1987], cytochrome c with plastocyanin [Zhou and Kostic, 1992], hydrogenase with cytochrome C3, rubredoxin, ferredoxin and flavodoxin [Bell et al, 1978], cytochrome C3 with ferredoxin [Moura, J.J.G. et al, 1977;Xavier and Moura, 1978;Xavier et al, 1979;Guerlesquin et al, 1984Guerlesquin et al, , 1985Guerlesquin et al, and 1987Capeill~re-Blandin et al, 1986;Cambillau et al, 1988, Park et al, 1991, cytochrome C3 with rubredoxin [Moura, I. et al, 1980a;Stewart et al, 1989], cytochrome C3 with flavodoxin [Moura, I. et al, 1980a;Stewart et al, 1988] and a macro inorganic anion [Mus-Veteau et al, 1992].…”