Electrochemically converted proteins

It has been postulated that complexes of electron-transfer proteins in a membrane are of graduated redox-potential. The electron transfer occurs through channels provided by a complex sequence of ligands and bonds are conjugated molecules like carotenoids. These proteins are able to accept electrons from excited Chi on one membrane side (anode) and donate them to an acceptor of more positive redox potential on the other side (cathode). The membrane provides a resistance for an ion current from anode to cathode which closes the electrochemical circuit, and converts excitation energy into chemical free energy AG (Figure 9.4 b). 

In virtually every animal cell type, the concentration of Na+ is lower in the cell than in the surrounding medium, and the concentration of K+ is higher (Fig. 11-36). This imbalance is maintained by a primary active transport system in the plasma membrane. The enzyme Na+K+ ATPase, discovered by Jens Slcou in 1957, couples breakdown of ATP to the simultaneous movement of both Na+ and K+ against their electrochemical gradients. For each molecule of ATP converted to ADP and I , the transporter moves two K+ ions inward and three Na+ ions outward across the plasma membrane. The Na+K+ ATPase is an integral protein with two subunits (Mr -50,000 and -110,000), both of which span the membrane. 

Methylomas microorganisms are used to convert methanol to singlecell protein. The process conditions are similar to the methane process, but the cells are harvested by electrochemical aggregation and filtration. 

This approach has been adopted to investigate the function of COX from the proteobacterium Rhodohacter sphaeroides [110], the last enzyme in the respiratory electron transport chain of bacteria, located in the bacterial inner membrane. It receives one electron from each of four ferrocytochrome c molecules, located on the periplasmic side of the membrane, and transfers them to one oxygen molecule, converting it into two water molecules. In the process, it binds four protons from the cytoplasm to make water, and in addition translocates four protons from the cytoplasm to the periplasm, to establish a proton electrochemical potential difference across the membrane. In this ptBLM, the orientation of the protein with respect to the membrane normal depends on the location of the histidine stretch... 

The energy of the excited state is converted into electrochemical potential energy at the reaction center, which contains a primary electron donor P that transfers an electron to a nearby acceptor Ai within the same protein (and P... 

In phase 2 of cellular respiration, the energy derived from fuel oxidation is converted to the high-energy phosphate bonds of ATP by the process of oxidative phosphorylation (see Fig. 2). Electrons are transferred from NADH and FAD(2H) to O2 by the electron transport chain, a series of electron transfer proteins that are located in the inner mitochondrial membrane. Oxidation of NADH and FAD(2H) by O2 generates an electrochemical potential across the inner mitochondrial membrane in the form of a transmembrane proton gradient (Ap). This electrochemical potential drives the synthesis of ATP form ADP and Pi by a transmembrane enzyme called ATP synthase (or FoFjATPase). 

Vitamin K HPLC has provided the first assay of the phylloquinones and menaquinones that constitute vitamin K in plasma. Phylloquinone circulates bound to lipoproteins from which it can be extracted with hexane after ethanol protein precipitation. Removal of co-eluted lipids can be achieved with normal-phase cartridge columns. Reversed-phase HPLC is almost universally used for vitamin K measurement. Either UV (270 nm) or electrochemical detection is suitable. Electrochemical detection uses the reductive mode ( —1.3 V) to convert the quinone moiety to hydroquinone the main disadvantage being the need to remove oxygen from the mobile phase. 

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