Cobalt forms a component of which of the following vitamins?

Central poion of vitamin B12 consists of four reduced and extensively substituted 'pyrrole rings' surrounding a single cobalt atom(Co). This central structure is called 'corrin ring system'. When cyanide is bound to cobalt atom is called as cyanocobalamin. Cobalt is required only as a constituent of vitamin B12. While biotin, vitamin A and tochopherol has no metal as constituent pa. Also Know: Strict vegetarians (vegans) are at risk of developing B12 deficiency. Vitamin B12 is absorbed bound to intrinsic factor, a small glycoprotein secreted by the parietal cells of the gastric mucosa. Vitamin B12 is absorbed from the distal third of the ileum receptors that bind the intrinsic factor-vitamin B12 complex, but not free intrinsic factor or free vitamin. Ref: Bender D.A. (2011). Chapter 44. Micronutrients: Vitamins & Minerals. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper's Illustrated Biochemistry, 29e.