Vitamin B12, a coenzyme for a variety of enzymes. It is essential for deoxyribose synthesis. The vitamin is characterized by a tetrapyrole ring system similar to that of heme (q.v.). The molecule contains a central cobalt atom linked to four pyrrole nitrogens. The vitamin is unique in being synthesized only by microorganisms. See Chronology, 1964, Hodgkin.
Subjects: Chemistry — Genetics and Genomics.