Vitamin isotopic

The study of the biosynthesis of vitamin B 2 is a saga whose resolution, due primarily to Battersby (80—83) and Scott (84,85), requited an effort on the same magnitude as the total synthesis. It was only when recent molecular biology tools became available to complement en2ymology, isotopic labeling, chemical synthesis, and spectroscopy that solution of this problem became possible. 

C.-S. You, R. S. Parker, and J. E. Swanson, Bio availability and vitamin A value of carotenes from red palm oil assessed by an extrinsic isotope reference method, Asia Pac. J. Clin. Nutr. 11 (2002) S348-S442. 

Vitamin B12s reacts rapidly with alkyl iodides (e.g., methyl iodide or a 5 -chloro derivative of adenosine) via nucleophilic displacement to form the alkyl cobalt forms of vitamin B12 (Eq. 16-31). These reactions provide a convenient way of preparing isotopically labeled alkyl cobalamins, including those selectively... 

HAWORTH. SIR WALTER N. 0883-1950). An English chemist who received the Nobel prize in chemistry in 1937 along with Paul Karrer. He recommended the name ascorbic acid and synthesized vitamin C, He accomplished much work on carbohydrate structure und developed a substitute for blood plasma using carbohydrates. During World War 11. he developed gaseous diffusion separation on uranium isotopes. He received his Ph D. in Manchester. England. 

Radiation is used in medicine in the form of X-rays and radioactive isotopes. It is used in industry in many ways, e.g., as vitamin activator, sterilizing agents, and polymerization initiator it is also the basis of all types of spectroscopic analysis.)... 

It is usual to give a test dose of between 0.5 and 1.0 pg of the labeled vitamin for the standard Schilling test, and in the case of the dual-isotope technique 0.25 pg each of 57Co- and 58Co-labeled vitamin. It has been found... 

Brugge et al. (B21) described a simple dual-isotope test for pancreatic exocrine function. They gave their patients radiolabeled [57Co]Bl2 bound to R-protein and [58Co]B12 bound to intrinsic factor if significantly less of the R-protein-bound vitamin was absorbed compared to the intrinsic-factor-bound vitamin this provided good evidence for pancreatic exocrine dysfunction. 

F6. Fairbanks, V. F., Wahner, H. W., Valley, T. B., and Scheldt, R. M., Spurious results from dual-isotope (Dicopac) vitamin B12 absorption test due to rapid or variable rates of exchange of Co-B for 57Co-B12 bound to intrinsic factor. Nucl. Med. Commun. 4, 17-23 (1983). 

Taylor (10) also showed that high resolution was possible with FAB and that it could be applied to ions as large as these vitamins. However, higher resolution at high masses becomes essential, not for empirical formula determination (which for metal containing systems is often done better by a fit to the isotopic abundance patterns), but simply to be sure of resolving nominal masses as the molecules studied get heavier. 

A method of determining airborne iodine has also been reported.241 Here, iodine is absorbed into 5% aqueous KI and spectrophotometrically determined at 590 nm in the form of its complex with starch. This method is selective with respect to bromine and chlorine, and the sensitivity of this method is 0.25 mg of I2 per m3 of air. The concentration of the, 31I isotope in water can be determined by a method involving isotope exchange in the starch-iodine complex.242 Flow-injection determination of ascorbic acid (0.1-40 mg/mL) has been proposed.243 Iodine is generated in the flow system as I3- ions, which are in turn exposed to starch to produce a steady signal at 350 and 580 nm. Ascorbic acid provides inversed maxima which are measured. This method is recommended for analysis of ascorbic acid in fruit juice, jam, and vitamin-C preparations. Use of the blue complex has also been reported for determination of sodium dichloro-isocyanurate in air.244 Obviously the blue reaction is applicable in the determination of amylose, amylopectin, and starch,245-252 as well as modified starches.245,253-255... 

We have used stable Isotopes in several other zinc absorption studies. Sample analysis Is In progress from a study In which Zn was used to determine the effects of phtate and cellulose on zinc absorption In man. Studies were also conducted to determine zinc absorption from vegetarian diets, the effect of vitamin B-6 status on zinc absorption, and the effect of level of dietary zinc on zinc and copper absorption. 

Stable isotopes of retinal and (3-carotene have also been employed to assess liver vitamin A stores in healthy individuals, and the best measure of vitamin A status (Furr et ah, 1989). The relative ratio of circulating isotopically labeled retinol is later assessed to estimate liver levels (Wang et ak, 2000 Hickenbottom et ah, 2002b) and without this technique, a liver biopsy would be necessary to estimate liver levels. 

Furr, H.C. Amedee-Manesme, O. Clifford, A.J. Bergen, H.R. 3rd. Jones, A.D. Anderson, D.P. Olson, J.A. 1989. Vitamin A concentrations in liver determined by isotope dilution assay with tetradeuterated vitamin A and by biopsy in generally healthy adult humans. Am. J. Clin. Nutr. 49 713-716. 

Replacement of Metabolic Losses An alternative approach to determining vitamin requirements is to measure the loss from the body pool in a steady state. This requires estimation of the total body pool, and measurement of the fractional rate of loss from that pool, generally using radioactive or stable isotope tracers. Three problems can arise in such studies. 

Liver reserves of vitamin A can be estimated by isotope dilution after a test dose of isotopicaUy labeled retinol, but this is not a suitable technique for assessment of status in population studies. 

Vitamin Be requirements have been estimated both by isotopic tracer studies to determine turnover of the body pool (Section 9.6.1) and also by depletion/ repletion studies using a variety of indices of status (Section 9.6.2). These studies have generally been conducted on young adults, and there is inadequate information to determine the requirements of elderly people, because apparent status assessed by a variety of indices declines with increasing age, despite intake as great as in younger people (Bates et al., 1999a). As discussed in Section 9.6.3, there is also inadequate information to estimate the requirements of infants. 

There is a variety of estimates of the body pool of vitamin Be. Short-term studies with isotopic tracers suggest a total body content of between 160 to 600 ixmo (40 to 150 mg), with a half-life of 33 days, suggesting a minimum requirement for replacement in the wide range between 0.6 to 2.27 mg per day. 

A modified technique permits determination of the absorption in the presence and absence of exogenous intrinsic factor at the same time, by giving intrinsic factor-[ Co] vitamin B12 complex and free [ Co]vitamin B12 together, and measuring the relative amounts of each isotope excreted in the urine. 

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