Reaction centers in lipids

Specific functional role of physiologically important lipids of the photosynthetic membrane (phosphatidylcholine, cardiolipin and phosphaticlylglycerol) was investigated on the thermodynamic and kinetic requirements of the charge movements in bacterial reaction centers. The major effect of these lipids is to increase the stabilization of the separated caharges induced by light excitation during the photosynthetic energy conversion. It can be achieved by (1) changing the redox midpoint potential of the Q(A)/Q(A)(-) and Q(B)/Q(B)(-) redox couples, which results in the increase of the free energy gap that drives the Q(A)(_) to Q(B) electron transfer or (2) by changing the quinone binding/unbinding equilibrium. This study provides evidence that from kinetic point of view the P(+)Q(A)(-)Q(B) -> P(+)Q(A)Q(B)(-) charge transfer is mainly driven by the change in the enthalpy in LDAO and PC, whereas the entropy contribution is larger if negatively charged lipids are introduced.