Cobalamins holotranscobalamin

Herbert, V., Fong, W, Guile, V, and Stopler, T. (1990. Low holotranscobalamin II is the earliest serum marker for subnormal vitamin Bn (cobalamin) absorption in patients with AIDE. Am. ]. Hematol. 34,132-139. 

The measurement of holotranscobalamin II is potentially useftil as a specific marker of biologically available vitamin Bi2, because only cobalamin bound to Tell is specifically available for uptake by aU cells. Other methods have been described for the measurement of holotranscobalamin in serum, one using an immobilized monoclonal antibody to human transcobalamin, followed by measurement of released cobalamin by CPB, This method is currently available as a commercial kit. The other method uses magnetic beads coated with cobalamin to precipitate apotranscobalamin followed by measurement of the holotranscobalamin in the supernatant by ELISA. Though these methods are claimed to be precise and simple to perform, there remains doubt over the interpretation of the measured concentrations, and over their sensitivity and specificity in the diagnosis of vitamin B deficiency. ... 

Holotranscobalamin (holoTC) HoloTC is cobalamin bound to transcobalamin and this is the available cobalamin for the cells. There is now a debate as to whether measurement of holoTC is a better marker for identifying individuals with cobalamin deficiency than total serum cobalamin. 

Valente, E., Scott, J.M., Ueland, P.M., Cunningham, C., Casey, M., and Molloy, A.M., 2011. Diagnostic accuracy of holotranscobalamin, methylmalonic acid, serum cobalamin, and other indicators of tissue vitamin B12 status in the elderly. Clinical Chemistry. 57 856-863. 

Holotranscobalamin (holoTC, or active B12), the cobalamin-transcobalamin II complex released into the portal circulation and recognized by ubiquitous specific receptors, is considered the specific Cbl-saturated transporter, the biologically active form of vitamin B12. Only 6-20% of total circulating vitamin... 

Holotranscobalamin (transcobalamin Il-cobalamin complex) a minor fraction (about 20%) of circulating vitamin B12 and, thanks to specific ubiquitous receptors, its active form (active B12). 

Carmel, R., 2011. Biomarkers of cobalamin (vitamin B-12) status in the epidemiologic setting a critical overview of context, appKcations, and performance characteristics of cobalamin, methylmalonic add, and holotranscobalamin II. The American Journal of Clinical Nutrition. 94 348S-358S. 

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