Chapter 3 - Sunlight, Purple Bacteria, and Quantum Mechanics: How Purple Bacteria Harness Quantum Mechanics for Efficient Light Harvesting

Abstract

Publisher Summary This chapter provides an overview of the basic (quantum mechanical) features of the light-harvesting apparatus found in purple bacteria. It discusses the B850 assembly of the peripheral complex LH2 of purple bacteria as an example of the clever exploitation of quantum mechanics to produce an efficient light-harvesting system. Purple photosynthetic bacteria have evolved a well-designed system of modular units that make up the light-harvesting apparatus. These modules consist of pairs of hydrophobic, low-molecular weight polypeptides, called α and β (usually 50–60 amino acids long) that noncovalently bind a small number of bacteriochlorophyll (Bchl a) and carotenoid (Car) molecules. Most purple bacteria have two main types of complexes: the core complex (RC-LH1) and the LH2. In vivo , the whole light-harvesting structure is highly optimized for capturing light energy and funneling it to the reaction center (RC). There are several advantages of the purple bacteria group. First, their antenna (energy-transfer components) and reaction center (charge-transfer components) pigment proteins can be separated biochemically. Second, their different pigment groups are spectrally well separated, which makes functional studies much easier to interpret compared with chlorophyll-containing photosynthetic organisms.