Nl. Pucheu et al., BIOENERGETIC FACTORS CONTROLLING IN-VITRO PHOSPHORYLATION OF LHI-ALPHA (B870) POLYPEPTIDES IN MEMBRANES ISOLATED FROM RHODOBACTER-CAPSULATUS, Archives of microbiology, 165(2), 1996, pp. 119-125
Membranes of Rhodobacter capsulatus strain U43 (pTX35) showed qualitat
ively very similar phosphorylation patterns under in vitro and in vivo
conditions. In vitro, it was irrelevant whether the phosphate source
was orthophosphate or ATP. Inhibitors of electron transport did not in
hibit light-harvesting complex I (LHI alpha) (B870) polypeptide phosph
orylation, except for o-phenanthroline, which was strongly inhibitory.
Redox conditions regulated the amount of protein phosphorylated; exte
rnal redox potentials between +200 and +300 mV promoted the reaction.
Phosphorylation was inhibited by uncouplers such as carbonyl cyanide n
z-chlorophenyl hydrazone and nigericin plus valinomycin plus potassium
ions. Inhibitors of the H+-ATPase were also inhibitory when the phosp
hate source was [P-32]P-i or [gamma-P-32]ATP. From these results, it w
as concluded that an operative reaction center, a coupled membrane, an
d external redox potentials higher than +200 mV are required for optim
um LHI alpha phosphorylation. We also demonstrated that phosphorylatio
n of LHI alpha polypeptide occurs before insertion into the membrane a
nd that phosphate is preferentially incorporated into specific domains
within the cytoplasmic membrane. Intracytoplasmic membranes, identifi
ed here as light membranes, were found to contain a dephosphorylated L
HI alpha polypeptide.