Effect of trypsin on D1/D 2-cytochrom b 559 Photosystem 2 reaction center complex and reaction center from Rhodopseudomonas viridis.

Proteolytic enzyme (trypsin) was used to structurally alter the RCs isolated from plant and bacterium as a way of probing the relation between structure (chromophore-apoprotein interactions) and function (photochemical activity). It was found that neither spectral characteristics (absorption spectrum, the 4th derivative of absorption spectrum) nor photochemical activity (pheophytine photoreduction, P680 photooxidation, etc.) were changed dramatically in D1/D2/cytochrom b 559 PS 2 reaction center complex digested with trypsin. The PS 2 RC treated with trypsin migrates by one green band during electrophoresis with dodecylmaltoside. The peptides with a molecular mass higher than 3-4 kDa were not separated from PS 2 RC. These data indicate that digestion of D1 and D2 proteins does not disturb yet the conformation of peptides or their interactions in so-called 'core' of RC and the native state of pigments. In contrast to that, the RC from Rhodopseudomonas viridis treated with enzyme has changed absorption spectrum and lost photochemical activity. The stability of the bacterial RC increased after exchange of LDAO by dodecylmaltoside.