0- The sodium-potassium ATPase:
- Na+/K+-ATPase is an enzyme found in the plasma membrane. It is sodium-potassium adenosine triphosphatase, also known as the 'Na+/K+ pump', 'sodium-potassium pump', or simply 'sodium pump', for short.
- The enzyme moves Na+ ions out of the cell and replaces them with K+ ions. This keeps the Na+ ions outside of the cell membrane, and keeps the K+ ions on the inside of the cell membrane. The process works in the opposite direction of diffusion.
- For every three sodium ions that get pumped out of the cell, two potassium ions get pumped into the cell. One phosphate group is still bound to the pump.
- Cobalamine and cobalt proteins Cobalamin (vitamin B12) is a structurally complex cofactor, consisting of a modified tetrapyrrole with a centrally chelated cobalt.
- Cobalamin is usually found in one of two biologically active forms: methylcobalamin and adocobalamin. Most prokaryotes, as well as animals, have cobalamin-dependent enzymes, whereas plants and fungi do not appear to use it. In bacteria and archaea, these include methionine synthase, ribonucleotide reductase, glutamate and methylmalonyl-CoA mutases, ethanolamine ammonia lyase, and diol dehydratase.
- The principal cobalamins are: cyanocobalamin, hydroxocobalamin and the two coenzyme forms: methylcobalamin and 5-deoxyadenosylcobalamin (adenosylcobalamin). Vitamins are organic compounds required in the diet in, usually, very small amounts. They are conveniently classed as fat soluble (A, D, E and K) or water soluble (C and the B complex).
- Vitamin B12 is important for the normal functioning of the brain and nervous system and for the formation of blood.
- It is involved in the metabolism of every cell of the body, especially affecting DNA synthesis and regulation but also fatty acid synthesis and energy production. Its effects are still not completely known. Vitamin B12 (cobalamin) derived cofactors are used for two important reactions in humans:
- 1. Methylmalonyl CoA mutase requires 5-deoxyadenosylcobalamin (known as adenosylcobalamin Mutase carbon chain rearrangement – shifts CH3’s about. – involved in fat metabolism.
- 2. Methionine synthase (cofactor methylcobalamin) catalyses the conversion of homocysteine to methionine and tetrahydrofolate is also formed) – this is a Methyl Transferase (MTA) – important in production of red blood cells. The second reaction taking Methionine back to Homocysteine is catalysed by Methionine Synthase Reductase.
- Vitamin B12 is the only, metal-containing vitamin – it is also a water-soluble vitamin that is stored in the liver and must come from the diet.
