Ion Current,Electrochemical Potential,Redox Chains,Chromophore,Halobacteria,Bacteriochlorophyl

Ion Current

	Ion Current It is the flow of an ion from a higher to a lower electrochemical potential. It usually involves circulation across the membrane between two separate transport processes Outward electrogenic transport of protons is carried out by primary pumps which are vectorial enzymic pathways. Four types of primary pumps have been recognized in bacteria.
1. Redox chains. Dehydrogenation reactions in a redox loop carry hydrogen from a donor on the inner surface to an acceptor on the outer. Electrons return to the cytoplasmic side, while the protons are released outside. 2. Bacteriochlorophyll based photosynthesis. Light protons generate a primary electrical field which is converted by redox reactions into 3n electrochemical proton gradient. Here also the primary acceptor and electron donor are situated on opposite surfaces of the membrane.
3. Halobacteria contain a simple proton pump consisting of one protein species and retinal (chromophore). Retinal is bleached on illumination, releasing one proton (per proton absorbed) to the outside. Uptake of a photon from the cytoplasm brings about regeneration 4. Proton translocating ATPase consists of a headpiece (F1) and a base piece (Fo) in which there is a specific proton channel spanning the membrane.