Corrinoids: Cyclic TETRAPYRROLES based on the corrin skeleton.CobamidesVitamin B 12: A cobalt-containing coordination compound produced by intestinal micro-organisms and found also in soil and water. Higher plants do not concentrate vitamin B 12 from the soil and so are a poor source of the substance as compared with animal tissues. INTRINSIC FACTOR is important for the assimilation of vitamin B 12.Transcobalamins: A group of carrier proteins which bind with VITAMIN B12 in the BLOOD and aid in its transport. Transcobalamin I migrates electrophoretically as a beta-globulin, while transcobalamins II and III migrate as alpha-globulins.Cobalt: A trace element that is a component of vitamin B12. It has the atomic symbol Co, atomic number 27, and atomic weight 58.93. It is used in nuclear weapons, alloys, and pigments. Deficiency in animals leads to anemia; its excess in humans can lead to erythrocytosis.Tetrachloroethylene: A chlorinated hydrocarbon used as an industrial solvent and cooling liquid in electrical transformers. It is a potential carcinogen.Chemistry: A basic science concerned with the composition, structure, and properties of matter; and the reactions that occur between substances and the associated energy exchange.