The effect of chemical additives on the bacteriorhodopsin photocycle

It is demonstrated that gelatin is very effective for preparing dried sampl es of bacteriorhodopsin because it does not change the spectra and the phot ocycle of the protein, but helps to form a very smooth and stable purple me mbrane multilayer on the glass surface. In this way, the effect of other ch emical additives on the photocycle of dried samples of bacteriorhodopsin ca n be studied, To gain information about the effect of triethanolamine on th e photocycle, optical absorption kinetic measurements have been carried out on dried samples of bacteriorhodopsin in a gelatin matrix at different add itive concentrations and humidities. Negligible effects are observed on the signals measured in suspension with gelatin and triethanolamine. The photo cycle of dried sample slows by two orders of magnitude in the presence of 2 00-250 molecules of triethanolamine per protein. The effect of water conten t on the chemically treated dried samples has been studied, giving the long est lifetime at 0.5 relative humidity. To understand the mechanism of triet hanolamine, several bacteriorhodopsin mutants have been investigated. (C) 1 999 Elsevier Science S.A. All rights reserved.