Slowing of proton transport processes in the structure of bacterial reaction centers and bacteriorhodopsin in the presence of dipyridamole

Dipyridamole, 2,6-bis(diethanolamino)-4,8-dipiperidinopyrimido, is employed in clinical practice as a vasodilator. It can also inhibit a specific memb rane protein (glycoprotein P) which pumps anticancer drugs out of tumor cel ls. Dipyridamole (10(-4) M) markedly slows down the kinetics of the electro genic phase of the photoelectric response in Rhodobacter sphaeroides chroma tophores. This phase is due to proton transfer from the external medium to the secondary quinone acceptor in the reaction center. In purple membranes of bacterium Halobacterium salinarium containing bacteriorhodopsin dipyrida mole (in its charged state) significantly slowed the kinetics of proton tra nsfer from the primary donor, Asp-96 (in membranes from bacteria of wild ty pe), or from the external medium (in D96N mutant) to the Schiff base. It is suggested that dipyridamole can influence the structural-dynamic state of membrane proteins including modification of the structure of their hydrogen bonds involved in proton-transport processes.