Membranes energy converting

The carbonic anhydrase (Cam) in M. thermophila cells is elevated several fold when the energy source is shifted to acetate, suggesting a role for this enzyme in the acetate-fermentation pathway. It is proposed that Cam functions outside the cell membrane to convert CO2 to a charged species (reaction A4) thereby facilitating removal of product from the cytoplasm. Cam is the prototype of a new class (y) of carbonic anhydrases, independently evolved from the other two classes (a and P). The crystal structure of Cam reveals a novel left-handed parallel P-helix fold (Kisker et al. 1996). Apart from the histidines ligating zinc, the activesite residues of Cam have no recognizable analogs in the active sites of the a- and P-classes. Kinetic analyses establish that the enzyme has a zinc-hydroxide mechanism similar to that of Cab (Alber et al. 1999). 

A fuel cell is a device in which the reactants, for example hydrogen and oxygen, are each continuously supplied to opposite sides of a suitable membrane and converted to electrical energy. 

Bennett s team has developed an artificial photosynthetic membrane to convert sunlight into energy [134]. 

Bacteriorhodopsin is the protein component of the purple membrane it resembles the visual pigment rhodopsin and acts as a light-energy converting system. It is part of a simple photosynthetic system in halobacteria that live in the Bay area near San Francisco and cause its characteristic orange-red color. Oesterhelt, by then in Wurzburg, hired Hartmut to purify and crystallize bacteriorhodopsin. When Oesterhelt moved to Martinsried to become Director of the Max Planck Institute for Biochemistry, Hartmut went with him, and this is how we met. 

There were so many data around about photosynthesis, especially about spectroscopy and electron transfer rates, but it was a black box. There were spectra and there were numbers, and with the three-dimensional structure this black box was suddenly illuminated. For the first time we saw and understood how light energy converted into electric current across the membrane. 

Key intermediate energy-converting steps common to both photosynthesis and respiration are (1) the cyclic reduction and oxidation of nicotinamides and flavins coupled to the pumping of acid (protons) from one side to the other of a membrane and (2) the return of acid (protons) across the membrane coupled to production of ATP. 

Photosynthesis in photosynthetic bacteria involves light driven electron transfer across a bilayer lipid membrane which converts the light energy into chemical potential. After transmembrane charge separation, the chemical potential is in the form of reducing equivalents on the cytoplasmic side of the membrane, oxidizing equivalents on the periplasmic side and a membrane potential of perhaps 180 mV which is negative on the cytoplasmic side. From the crystal structure of the reaction center of Rb. sphaeroides (Yeates et (1988)) it is possible to construct an illustration of the supramolecular structure which accomplishes this process (Fig. 1). 

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