Chlorophyll-Binding Proteins (CAB, chlorophyll A and B binding proteins, light-harvesting chlorophyll protein complex, LHCP)

Chlorophyll-binding proteins are situated in the membrane of the thylakoids. They modify the plane of orientation of chlorophylls. Due to this modification the chlorophyll does not fluoresce when excited by visible light (as it would do without CAB). The light energy absorbed by (an antenna) chlorophyll is rather transferred to a neighboring chlorophyll molecule and then excites this second chlorophyll while the first one returns to the ground state. This resonance energy transfer is continued to further neighbors until the photochemical reaction center is reached. In this molecule an electron is raised to a higher energy orbital, and this electron is transferred to the electron transfer chainof the chloroplast resulting in an electron hole (empty orbital). The electron acceptor thus gains a negative charge and the lost electron by the reaction center is replaced by another electron coming from a neighbor molecule, which therefore becomes positively charged. As a consequence, the...