PRESSURE EFFECTS ON SPECTRA OF PHOTOSYNTHETIC LIGHT-HARVESTING PIGMENT-PROTEIN COMPLEXES

The influence of high (up to 9 kbar) hydrostatic pressure on the absor ption and fluorescence emission spectra of photosynthetic light-harves ting pigment-protein complexes isolated from purple bacteria Rhodospir illum rubrum has been studied at room temperature and at 77 K. Under p ressure at room temperature all spectral bands exhibit a red-shift at a rate of between 30 and 120 cm-1/kbar for different bands. From these pressure shifts the compressibility of the protein matrix can be esti mated. The compressibility is remarkably different for the protein sur rounding bacteriochlorophyll a molecules (kappa greater-than-or-equal- to 25 +/- 5 Mbar-1) than for the one surrounding spirilloxanthin molec ules (kappa = 10 +/- 2 Mbar-1). This indicates that the elastic proper ties of a protein are locally specific.