Vitamin availability

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). 

The leucocyte method estimates pyridoxal phosphate in isolated leucocytes it is based on a coenzyme-catalyzed tyrosine decarboxylase system from S. faecalis (B32). Enough data are not yet on hand to evaluate this method. The determination of circulating or available vitamin Ba should offer a more direct approach. 

Technologists should become aware of possible reduction of available vitamins due to such processing as some vitamins can be considered marginally deficient in American diets. This concern is especially important in those modified protein foodstuffs that can contribute a sizable portion of our daily calories. 

Pernicious anemia is usually caused by poor absorption of the vitamin. Absorption depends upon the intrinsic factor, a mucoprotein (or rnuco-proteins) synthesized by the stomach lining.ad 1 Pernicious anemia patients often have a genetic predilection toward decreased synthesis of the intrinsic factor. Gastrectomy, which decreases synthesis of the intrinsic factor, or infection with fish tapeworms, which compete for available vitamin B12 and interfere with absorption, can also induce the disease. Also essential are a plasma membrane receptors 1 and two blood transport proteins... 

This experiment is flexible in that students may choose the samples they wish to analyze. It is suggested that several fruits and vegetables as well as an unknown ascorbic acid sample be available for analysis. The vitamin C content of raw and cooked vegetables can also be measured and compared. Commercially available vitamin C tablets or multivitamin pills provide interesting samples for analysis. The time required for this experiment can be adjusted by controlling the number and type of samples. 

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. ... 

Cobalmin Deficiency. Pernicious anemia is the disease associated with vitamin Bi2 deficiency. It is usually caused by the inability to produce intrinsic factor. Indeed, many times the vitamin must be administered by injection. The blood picture, a megaloblastic anemia, is indistinguishable from that caused by folic acid deficiency. Indeed folic acid supplements can mask the blood picture. This is illustrated in Fig. 8.53. Removal of ad-enosyl cobalamin eliminates the regeneration of tetrahydrofolate during the methylation of homocysteine to methionine. Folic acid supplements provide a fresh source of tetrahydrofolate coenzymes. DNA synthesis can continue and new erythrocytes form. Excess folic acid also may compete for the available vitamin, further exacerbating vitamin deficiency. 

Ando, K., Koike, E, Kondo, E, and Takayama, H., An improved synthesis of 24,24-difluoro-la,25-dihydroxyvitamin Dj from readily available vitamin Dj, Chem. Pharm. Bull., 43, 189, 1995. 

Apart from the technical route described to p-apo-8 -carotenal, readily available vitamin A alcohol (Cjo) has served as an intermediate in the form of the phosphonium salt by reaction with the monodiethyl acetal of a Cio dial (ref. 54). The required Cjo monodiethylacetal was obtained (ref.5, p409) by the reaction of the mono aldehyde-protected derivative, the enol ether of methylmalonaldehyde, (C4) with the acetylenic Grignard reagent from trans 3-methyl-2-penten-4-yn-l-ol (C ) followed by acidic dehydration and partial reduction with Lindlar catalyst to give firstly 8-hydroxy-2,6-dimethylocta-2, 4,6-triene-l-al (Cio). Protection of the hydroxyl group by acetylation in pyridine solution with acetyl chloride and formation of the diethyl acetal with ethyl orthoformate followed by hydrolysis of the acetyl group and oxidation afforded the final CIO aldehyde component (D)shown in Scheme 15a. 

Warfarin disrupts the recycling of vitamin K epoxide form to active vitamin K. This results in depletion of available vitamin K stores, and eventually to lack of activation of vitamin K-de-pendent clotting factors—particularly factors II, VII, IX and X (recall that vitamin K is converted to an inactive epoxide form after interaction with platelet factors, and must be recycled" back to its active form in the liver [see Figure]). 

Commercially available vitamin E consists of either a mixture of namrally occurring tocopherols and tocotriraiols (from natural sources), RRR-a-tocopherol (formerly called d-a-tocopherol), synthetic a-tocopherol, consisting of the eight possible side-chain stereoisomers at eqnal amonnts (all roc-a-tocopherol, formerly called dl-a-tocopherol), or their esters (a-tocophrayl succinate, a-tocopheryl acetate, a-toco-... 

The susceptibility of LDL toward oxidation can be tested in vitro and ex vivo. When LDL are isolated from human plasma and exposed to free copper ions, the amount or velocity of peroxides formed is measured. It is not until aU of the available vitamin E and other antioxidants have been consumed that LDL peroxidation occurs. In line with that theory, many studies have reported that higher intakes of PUFA (linolenate and n-3 LC-PUFA) increase LDL susceptibility to ex vivo oxidation (20-26). 

PN-glucoside serves as a source of nutritionally available vitamin Be, with 50% bioavailability relative to PN (Maeno et al. 1997 Nakano et al. 1997). 

Figure 15.4 demonstrates that the fluorescence intensity is linearly correlated with vitamin Bi concentrations in the range 0.026-16.83 pg mL . The relative standard deviation is 1.75% for six replicate measurements of 10 pg mL . The detection limit of vitamin Bi is 0.015 pg mL The method is applied to determine vitamin in commercially available vitamin Bi tablets (Biphane, Yuhan Co., Korea) to check the performance of the system (Table 15.1). The effect of the foreign substances that may influence the FL intensity was investigated to evaluate the selectivity of this method. The results indicated that most of the potentially interfering substances had very little or no effect on the... 

Two approaches have been used to evaluate the vitamin A value of diets a biological assay and a chemical assay. Biological assays in animals measure the total physiologically available vitamin A activity of the diet, i.e., not only retinol but also its active isomers. Biological assays, therefore, account for variable efficiencies in absorption, conversion, and utilization of preformed and precursor vitamin A sources. These assays were the standard technique for dietary evaluation in the older literature and continue to be used as the ultimate test even today. However, biological assays are time-consuming and expensive. 

As mentioned above, it is probable that menadione acts in preventing vitamin K deficiency only by its conversion into a vitamin K form containing an isoprene-like side chain. Together with the fact that menadione itself could not be found in nature, it seems logical to accept a vitamin Ki or a vitamin Kj form as the biological standard. In view of its easy availability, vitamin Ki would seem to be the most appropriate. 

When an intestinal disorder is present, especially if there is diarrhea, the small intestine may harbor large numbers of bacteria. These are likely to reduce, rather than increeise, the amounts of available vitamins. 

Vitamin B-6 intake in average U.S. diets—According to the U.S. Department of Agricuiture, the overaii average per capita avaiiabiiity of vitamin B-6 per day in the United States is 2.2 mg, not inciuding waste or cooking losses. Also, it is noteworthy that 40.5% of the available vitamin B-6 is provided by meat, poultry, and fish. 

It should be noted that incubation for as long as 10 days may be necessary to allow differentiation of growth with higher concentrations of vitamin B12. Growth continues until all available vitamin Bu has been used up, or until, with 150 uuMg-per milliliter or more, growth reaches the maximum concentration of about 5 to 7 million cells per milliliter. Absorption of vitamin Bu in concentrations of 50 MMg-per milliliter is rapid, and within two days of inoculation no vitamin Bu is detectable in the supernatant, indicating that cells absorb much more than their immediate... 

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