Spectroscopic Properties of Antenna Complexes from Purple Bacteria

Abstract

This chapter describes the known factors which shape the electronic (and thus the functional) properties of light-harvesting (LH) complexes of purple bacteria. Although a variety of high- and low-resolution structures from LH complexes are now available, they do not provide, per se, a detailed picture of the electronic properties of the pigments in these complexes. However they constitute a framework which has helped, through the use of wide range of techniques, most often combining site-selection mutagenesis and advanced spectroscopies, to make progress in determining which parameters are important for the function of these proteins. Today, antenna proteins from purple photosynthetic bacteria are probably the best-understood photosynthetic LH proteins, and among the best-characterized membrane proteins in any biological field. However, there are still some discrepancies about the precise relationship between their structure and function. This chapter attempts to describe, as simply as possible, the physical mechanisms which are thought to underlie the tuning of the absorption properties of bacteriochlorophyll molecules in these proteins, as well as the results which are at the origin of the running arguments.