Cobalamin hydroxo

Four cobalamins (hydroxo- cyano-, adenosyl-, methylcobalamin) and two cobi-namides (cyano-a- and cyano-] -cobinamide) were baseline resolved on a Cjg column = 278 nm) using a 30-min 90/10 -> 60/40 water (25 mM ammonium acetate to pH 4 with acetic acid)/methanol gradient [330]. Peak shapes were excellent. A linear range of 10-100 pg/mL and a detection limit of 2 pg/mL were reported. 

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). 

Red—anticholinergic agents (e.g., antihistamines, atropine, tricyclic antidepressants, scopalamine), disulfiram, hydroxo-cobalamin, and vancomycin... 

Methyl-Cobalamine and Related Compounds. There are three major types of cobalamine in animals and man, the methyl and hydroxo derivatives and the deoxyadenosyl derivative (coenzyme B12). The unique metal-carbon bond in the methyl derivative and in B12 is extremely photolabile, and their photolyses have been widely studied. However, radiolytic processes have not been widely studied. 

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... 

Bosma, T.N.P., F.H.M. Cottaar, M.S. Posthumus, C.J. Teunis, A. van Veidhuizen, G. Schraa, and A.J.B. Zehnder. 1994. Comparison of reductive dechlorination of hexachloro-1,3-butadiene in Rhine sediments and model systems with hydroxo-cobalamin. Environ. Sci. Technol. 28 1124-1128. 

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. 

Several TLC techniques have been applied here. Cima and Mantovan [16] have investigated the separation of cyanocobalamin and hydroxo-cobalamin using 20 different solvents on sihca gel G which was partly buffered. They isolated photochemical decomposition products at the same time. Covello and Schettino [21] have compared paper chromatographic procedures with some fast TLC systems which were especially... 

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... 

The detection system in HPLC is often based on ultraviolet (UV) light measurement of the effluent. Since the concentration of cobalamins in human samples is very low, our laboratory has developed a sophisticated method to determine low-level concentrations of HPLC-separated cobalamins (Hardlei and Nexo 2009). After immunoprecipitation of haptocorrin or transcobalamin followed by a proteolytic extraction and reversed-phase HPLC in darkness (to avoid conversion of methyl- and adenosyl-cobalamin into hydroxo-cobalamin), the fractions are vacuum-dried, re-dissolved in buffer and the cobalamin in the fractions is measured either by employing a sensitive cobalamin specific assay or an assay recognizing also the cobalamin analogues capable of measuring levels as low as 4pmol/L. 

Gimsing et al. (70) attributed the loss of hydroxo- and sulfitocobalamin during ethanol extraction to binding onto histidine residues of plasma proteins, a phenomenon already described by Bauriedel et al. (71), Taylor and Hanna (72), and Lien and Wood (73). This binding process is optimal at pH 7.3, has specificity for aquocobalamin but not sulfitocobalamin, increases in the presence of 5 M urea, and is competitively inhibited by Cd ions. In the histidine-bound form, Co -cobalamine should be more resistant to reductive agents than in the free form. 

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