Vitamin relative specific activities

Table VIII. Relative Specific Activities of Vitamin B12 Coenzyme, Residual Substrate, and Product During the Conversion of D-1,2-Propanediol-1 - H to Propionaldehyde-2- H...

In the liver, vitamin D is hydroxylated to 25-hydroxy vitamin D [25-(0H)2D], the principal circulating metabolite of vitamin D. In the kidney, hydroxylation at position 1 yields l,25-(OH)2D. This metabolite has the highest specific activity of the naturally occurring metabolites. 24,25-(0H)2D is also synthesized by renal mitochondria and in other tissues in relatively large amounts in animals with adequate intake of vitamin D, calcium, and... 

It was found that vitamin E deficiency in the rat resulted in an increase in the incorporation of formate-C into nucleic acids of liver and skeletal muscle (Dinning, 1955). The rats used in these experiments were only mildly deficient in vitamin E, and subsequent experiments were conducted on rabbits in which it is possible to produce severe vitamin E deficiency with relatively short feeding periods. Vitamin E deficiency in the rabbit led to an increased specific activity of nucleic acids in several tissues following formate-C injection (Dinning et al., 1955). Measurements of the specific activity of CO2 expired by these animals indicated that the overall formate pool size was not affected by vitamin E deficiency. The increased specific activity of the tissue nucleic acids then could represent an altered specific activity of the nucleotide precursors or an altered synthetic rate of the tissue nucleic acids. 

A radioisotope dilution assay and an assay based on animal growth are the most reliable methods for the determination of vitamin B12 activity. The tracer technique is highly specific for cyanocobalamin or analogs which are convertible to cyanocobalamin. The assay is specific for cyanocobalamin if cyanide treatment of the sample is avoided total cobalamins convertible to cyanocobalamin are determined if a given sample is first treated with cyanide. The method consists in the addition of a known amount of pure [ Co]-cyanocobalamin. A series of selective extractions and adsorptions to remove interfering substances is completed and the radioactivity and color of the purified sample are measured. From these data, it is possible to calculate the amount of cobalamin present in the original sample. The isotope dilution method is accurate and precise and can be used for both relatively pure samples and for crude extracts of low potency. 

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