Proton transfer in bacterial reaction centers and bacteriorhodopsin in thepresence of dipyridamole

Dipyridamole, 2,6-bis(diethanolamino)-4,8-dipiperidinopyrimido[5,4-d]pyrimi dine (DIP), a well known vasodilator and inhibitor of membrane peroxidation has recently been shown a potential co-activator (modulator) in the MR phe nomenon in cancer therapy. It inhibits P-glycoprotein (Pgp) which is a effl ux pump of anticancer drugs in tumor cells. For the first time it is shown that dipyridamole, markedly slows down the kinetics of the electrogenic pha se of the photoelectric response in Rb. sphaeroides chromatophores which is due to the proton transfer from the external medium to the secondary quino ne acceptor in the reaction center. In purple membranes from H. salinarium containing bacteriorhodopsin (bR) dipyridamole (in its charged state) signi ficantly slows down the kinetics of the proton transfer to the Schiff base from the primary donor Asp-96 (in wild type bacteria) or from the surroundi ng (in D96N mutant). Dipyridamole is supposed to affect the proton-transfer via changes in structural dynamics of membrane proteins including modifica tion of their system of hydrogen-bonds.