Cobalamin vitamin hydroxo

Vitamin B12 (Fig. 1) is defined as a group of cobalt-containing conoids known as cobalamins. The common features of the vitamers are a corrin ting (four reduced pyrrole rings) with cobalt as the central atom, a nucleotide-like compound and a variable ligand. Vitamin B12 is exceptional in as far as it is the only vitamin containing a metal-ion. The vitamers present in biological systems are hydroxo-, aquo-, methyl-, and 5 -deoxyadenosylcobalamin. 

Vitamin Bjj compounds with different upper (L) and lower (R) ligands were fonnd in natnre (Figure 10.3). Some commercially available vitamin Bjj reagents, hydroxo-cobalamin and dicyanocobinamide, contain small amounts of impnrities [9]. Each vitamin Bjj reagent should be purified with silica gel 60 TLC [2-pro-panol/NH40H(28%)/water (7 1 2, v/v) as a solvent] and then used for experiments as an authentic standard material (Figure 10.4). 

MushettCW, Kelley KL, Boxer GE, etal. 1952. Antidotal efficacy of vitamin B12 (hydroxo-cobalamin) in experimental cyanide poisoning. Proc Soc Exp Biol Med 81 234-247. 

Cyanocobalamin and the derivative hydroxo-cobalamin, given IM or deep subcutaneously, are indicated for treating vitamin B12 deficiency. Only in strict vegetarians oral preparations may be effective. Oral preparations with added intrinsic factor mostly are not reliably in patients with pernicious anemia. More than half the dose of cyanocobalamin injected is excreted in the urine within 48 hours and the therapeutic advantages of doses higher than 100 pg are questionable because of this rapid eiimination. As... 

Cyclic voltammetric studies reveal that methylcobinamide can be reduced by one electron to a Co -CHg species which rapidly dissociates with a rate constant of ca. 2.5 X 10 s at 19 °C in DMF-propanol solvent. Methylcobalamin is more reactive, with a dissociation rate of 1.2 x 10 s at — 30 °C. Redox between vitamin Riga and Biar is affectedby the presence or absence of axially bound benzimidazole base. This allows the determination of base-on, base-off rates by cyclic voltammetry. Values of 44 s and 0.18 s are reported for Biaa. The redox process is also affected by whether the cobalamin is in its aquo or its hydroxo form. 

Only cobalamin present on transcobalamin is available for the cells (for a review, see Quadros 2010), while the function of cobalamin bound to haptocorrin remains to be clarified (for an overview, see Morkbak et al. 2007). Transcobalamin carries both of the two co-enzymes, 5 -deoxy adenosyl-coba-lamin and methyl-cobalamin, and also other forms of the vitamin that can be converted into the coenzymes such as cyanocobalamin and hydroxo-cobalamin... 

---