Hydroxycobalamin

Aquocobalamin Hydroxycobalamin Vitamin Bj2a) antipernicious vitamin (depot form ... 

Hasham SA, DL Freedman (1999) Enhanced biotransformation of carbon tetrachloride by Acetobacterium woodii upon addition of hydroxycobalamin and fructose. Appl Environ Microbiol 65 4537-4542. 

Figure 15.3 Structural formula of deoxyadenosylcobalamin (coenzyme B, ). (a) A plan view of the corrin nucleus with substituents, (b) The position of the remaining two ligands of the cobalt atom. No attempt is made to show correct stereochemical relationships. Related compounds have different groups in place of the 5 -deoxyadenosyl group cyanocobalamin, (vitamin Bi2)-CN hydroxycobalamin, (vitamin Bi2)-0H methylcobalamin, (vitamin Bi2)-CH3.

Optimal therapy consists in parenteral administration of cyanocobalamin or hydroxycobalamin (Vitamin Lullmann, Color Atlas of Pharmacology... 

Aquacobalamin reductase (NADH) [EC 1.6.99.8] catalyzes the reaction of two aquacob(III)alamin with NADH to form 2 cob(II)alamin and NAD+. Aquacobalamin reductase (NADPH) [EC 1.6.99.11] catalyzes the exact same reaction, albeit with NADPH. In addition, this enzyme can utilize hydroxycobalamin as a substrate, but not cyanocobalamin. 

The name vitamin B12 indicates a group of cobalt-containing corrinoids, also described as cobala-mins. Hydroxycobalamin (HOCbl), adenosylcobalamin (AdoCbl), and methylcobalamin (MeCbl) are the natural occurring forms. Instead, cyanocobalamin (Figure 19.20) is the commercially available form used for supplements and food fortification, thanks to its greater relative stability. Occasionally, sulfitocobalmin can occur in processed foods. Vitamin B,2 functions as a coenzyme and it is linked to human growth, cell development, and is involved in metabolism of certain amino acids. Vitamin B12 is present mainly in meat and diary foods, therefore a deficiency can occur in... 

Bovine milk contains, on average, 0.4 fig Bi2 per 100 g. The predominant form is hydroxycobalamin and more than 95% of this nutrient is protein bound. The concentration of B12 in milk is influenced by the Co intake of the cow. The predominant source of B12 for the cow, and hence the ultimate origin of B12 in milk, is biosynthesis in the rumen. Therefore, its concentra-... 

Graham, J.P.D. (1965) Hydroxycobalamin as an antidote to acrylonitrile. Toxicol, appl. Pharmacol., 7, 367-372... 

Hydrolysis of deoxyadenosylcobalamin by acid (1 M HC1,100°, 90 min) yields hydroxycobalamin, adenine, and an unsaturated sugar (Eq. 16-33). The initial reaction step is thought to be protonation of the oxygen of the ribose ring. 

Scheffold and colleagues subsequently reported that alkyl iodides 249 add to xfl-unsaturated esters 248 catalyzed by 23 mol% hydroxycobalamine 247 (X=OH) and mediated by light to homolyze 253B [302]. The generation of the active Co(I) species 253A proceeded by electrochemical reduction at a potential of —1.2 V vs SCE. The transformation required a large excess of 248 to promote the addition of the initially generated alkyl radical. The reaction was applied to the total synthesis of the California red scale pheromone. The product... 

The TCII-vitamin B12 complex is recognized by specific high-affinity plasma membrane receptors present on the cells that utilize vitamin B12. After internalization, the complex is transferred to lysosomes, where TCII is rapidly degraded, and the hydroxycobalamin is released into the cytosol and methylated. The hydroxycobalamin that enters the mitochondria... 

CHLORAMPHENICOL VITAMIN B12 1 efficacy of hydroxycobalamin Chloramphenicol depresses the bone marrow this opposes the action of vitamin B12 Be aware monitor FBC and vitamin B12 levels closely... 

Brass EP, Allen RH, RuffLJ, and Stabler SP (1990) Effect of hydroxycobalamin[c-lactam] on propionate and carnitine metabolism in the rat. Biochemical Journal 266, 809-15. 

Use of cobalt chemistry that chelates the cyanide directly such as hydroxycobalamin. 

Borron, S.W., Stonerook, M., Reid, F. (2006). Efficacy of hydroxycobalamin for the treatment of acute cyanide poisoning in adult beagle dogs. Clin. Toxicol. 44 (Suppl. 1) 5-15. 

The second reaction requiring vitamin B12 catalyzes the conversion of homocysteine to methionine and is catalyzed by methionine synthase. This reaction results in the transfer of the methyl group from N -methyltetrahydrofolate to hydroxycobalamin generating tetrahydrofolate and methylcobalamin during the process of the conversion. 

Guerra R, Casu L. Hydroxycobalamin for ethambutol-induced optic neuropathy. Lancet 1981 2(8256) 1176. 

Heyworth-Smith D, Hogan PG. Allergy to hydroxycobalamin, with tolerance of cyanocobalamiiL Med J Aust 2002 177(3) 162-3. 

Pernicious anaemia was a fatal disease first reported in 1880. It was not until 1926 that it was discovered that eating raw liver effected a remission. The active principle was later isolated and called vitamin B12 or cyanocobalamin. It was initially obtained from liver but during the 1960s it was noted that it could be obtained as a by-product of microbial metabolism (Table 25.2). Hydroxycobalamin is the form of choice for therapeutic use and can be derived either by chemical transformation of cyanocobalamin or directly as a fermentation product. 

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