See paper for distribution of PS-I and PS-II within grana As explained in the ab
ID: 32317 • Letter: S
Question
See paper for distribution of PS-I and PS-II within grana
As explained in the above paper, the PS-I complex is primarily located within non-appressed thylakoid region and stroma lamella, while PS-II in the appressed regions. Now since non-cyclic electron transfer (non-cyclic photophosphorylation) requires both the photosystems, wouldn't their distribution within grana far from one another hamper their ability to carry out non-cyclic electron transport. Although there are mobile untis to account for the electron transport between marginal PS-I and the PS-II immediately below, but the electron transport to the PS-II units deep in the granal core would still be unaccounted for.
Explanation / Answer
First a clarification: the mobile units are no so "mobile". Due to (1) the high protein:lipid ratio of the thylakoid membrane and (2) the packing of protein complexes, the rapid diffusion of components along the membrane is hindered.
It has been proposed the existence of small local PQ diffusion microdomains, based upon the percolation theory:
From the percolation theory, above a critical density, immobile or slowly moving transmembrane proteins are, indeed, expected to form flexible 2D networks of closed compartments preventing long range movement of small molecules. (Kirchhoff, H et al. (2000) Biochim. Biophys. Acta 1459, 148