Photosynthetic Electron Transport System, Chemo Organotrophic Bacteria, Cytochrome, Ubiquinone

Photosynthetic Electron Transport System

	Photosynthetic Electron Transport System - The electron transport system of photosynthetic bacteria differs from that of aerobic chemoorganotrophic bacteria. Cytochrome a and other types of cytochrome oxidase are not present in the photosynthetic electron, transport system, because photosynthesis takes place under anaerobic conditions. Hence there is no need of a cytochrome which interacts with molecular oxygen.
The electron transport system consists of an intermediate electron acceptor (I). a primary electron acceptor (X), a secondary acceptor (Y), generally believed to be ubiquinone (UQ), and b- and c-type cytochromes. The electron transport carriers are asymmetrically located in the membrane. This is necessary for setting up the hydrogen ion gradient. Immunological studies suggest that the reaction centre spans the membrane of the chromotophore. It is probably located beneath the ATPase complex.
The primary acceptor X is believed to be associated with the reaction centre on the outer side of the membrane. The secondary acceptor Y, (probably UQ) takes protons from the medium. It is thus also located on the outer side.
The b-type cytochrome is probably located in the interior of the membrane. The c-type cytochrome interacts with the reaction centre and is located on the inside of the membrane.