Resonance Raman spectroscopy of chlorophyll-protein complexes

Abstract

Resonance Raman spectra of chlorophyll a (Chl a) and of Chl b were selectively obtained, at low temperature, from chlorophyll-protein complexes prepared from green and blue-green algae and from higher plants. Antenna Chl a in the Chl a-P700-protein complexes (CP I) and in the light-harvesting Chl a/b-protein complexes (CP ii gives resonance Raman spectra extremely close in all their features to those previously obtained from intact cells and chloroplasts. In particular, the same multiplicity of binding sites for the ketone carbonyl groups of Chl a is observed in both CP I and CP II as in intact membranes. These bindings sites are probably the same types as those observed in the intact membranes and are not the magnesium atoms of other chlorophylls. The magnesium atoms of most Chl a molecules in both CP I and CP II bind a single external ligand. Resonance Raman spectra of Chl b in CP II preparations, although very similar to those from intact membranes, show partial rearrangement of one of the two environmental subspecies of Chl b previously found in intact membranes. These results provide evidence that chlorophyll-protein complexes closely represent the state of the bulk of antenna chlorophyll in vivo.