ENERGETICS OF THE QUINONE ELECTRON-ACCEPTOR COMPLEX IN RUBRIVIVAX-GELATINOSUS

AGALIDIS I SEBBAN P

I. Agalidis et P. Sebban, ENERGETICS OF THE QUINONE ELECTRON-ACCEPTOR COMPLEX IN RUBRIVIVAX-GELATINOSUS, Biochimica et biophysica acta. Bioenergetics, 1232(3), 1995, pp. 180-186

43

INGLESE

Article

Biology,Biophysics

Biochimica et biophysica acta. Bioenergetics → ACNP

0005-2728

1232

3

1995

180 - 186

ISI

0005-2728(1995)1232:3<180:EOTQEC>2.0.ZU;2-H

The pH and temperature dependences of the free energy stabilization of the Q(A)(-) and Q(B)(-) semiquinone anions (Q(A) and Q(B) are respect ively the primary and secondary quinone electron accepters) were studi ed in antenna-reaction centre complex from Rubrivivax(R.) gelatinosus. This was achieved by measuring the rate constants of the P(+)Q(A)(-), (k(AP)) and P(+)Q(B)(-) (k(BP)) (P is the primary electron donor) cha rge recombination processes by flash-induced absorption spectroscopy. Despite the high primary sequence analogies of the Q(A) and Q(B) prote in pockets between R. gelatinosus and the much more studied species as Rps. viridis, Rb. sphaeroides and Rb. capsulatus, the energetic behav iour of the quinone complex of R. gelatinosus appears to be somewhat d ifferent: (i) above pH 10, k(AP) decreases, whereas it increases in Rp s. viridis; this suggests the presence of a protonatable group that st abilizes I- (I is a bacteriopheophytin electron acceptor) rather than Q(A)(-); (ii) the pH dependence of k(BP) is unusually flat in the rang e 4-7.5, possibly reflecting that a substantial part of the P(+)Q(B)(- ), charge recombination proceeds via the direct route through the prot ein by an electron tunnelling mechanism, at variance to what is observ ed in the three species mentioned above; (iii) the very substantial in crease of k(BP) observed above pH 7.5 is reasonably well described by the presence of two apparent protonatable groups: PK1QB = 9.4, pK(1QB- ),= 11 and pK(2QB) = 8.5, pK(2QB-) = 9.4. The latter group was not rep orted in Rps. viridis, Rb. sphaeroides or Rb. capsulatus. We conclude that the apparent pK values measured here in R. gelatinosus may reflec t the contribution as a whole of several and/or distant groups rather than of well-defined residues.