BINDING OF FE3-SPECTROSCOPY( IONS TO HALOBACTERIA PURP LE MEMBRANES AS STUDIED BY MOSSBAUER)

Purple membranes (PM) from Halobacterium halobium were reconstituted w ith Fe-57 ions and investigated by Mossbauer spectroscopy within the t emperature range from 5 to 300 K at the Fe/bacteriorhodopsin (BR) rati o 0.6-300. If the Fe/BR ratio was below 2, then Fe3+ bonds to PM mostl y as hydroxomonomeric particle [FeOH](2+). 5H(2)O, the apparent charge of the iron ion being two. If the Fe/BR ratio exceeds 2, the dimeric form [FeOH](4+.)(2) 8H(2)O along with a cluster form dominated. The te mperature dependencies of the mean square displacement show that the m obility of Fe ions changes from the solid-state type to the quasi-diff usional one at temperatures aver similar to 200 K and similar to 230 K for the dimeric or monomeric and cluster iron forms, respectively. Th e nature of the cation binding sites and their location on the PM surf ace are discussed. A possible role of the divalent cation binding to P M in the mechanism of the BR proton pumping is suggested.