This Vitamin is also known as cobalamine or cyanocobalamine, owing to the presence of the metal, cobalt.
Cyanocobalamine is used in most supplements because it is readily converted to active forms of vitamin B-12 in the body.
The central structure of the vitamin consists of a single cobalt atom surrounded by four pyrrole rings. This set up is called 'Corrin Ring' system. This cobalt atom is in turn covalently bounded to a cyanide group. It is hence called cyanocobalamine.
Vitamin B-12 is required for the conversion of homocysteine to methionine which is processed by enzymes. Vitamin B12 deficiency, like folic acid deficiency, can cause increased homocysteine in the blood.
Vitamin B-12 and folate are both necessary for the synthesis of raw materials that make up the DNA.