Vitamin species differences

Why then, since such an abundance of metabolic inhibitors is available, do so few of them find practical application Examples are the folic acid reductase inhibitors, such as aminopterin, the purine and pyrimidine analogs used as cytostatics in cancer chemotherapy and known for their high toxicity in a wide variety of species, and the organic phosphates and carbamates used as insecticides but also highly toxic to mammals. Lack of selectivity in the action of metabolic inhibitors is inherent in their mechanism of action due to the universality of biochemical processes and principles throughout nature. Selectivity in action requires species differences in biochemistry. For the antivitamins, for instance, there is not only a lack of species differences in action in addition, the fact that vitamins often serve as cofactors for a variety of enzymes is a serious drawback to endeavors to obtain agents with species-selective action. 

This method is dependent on the species. The vitamin requirements differ among the common laboratory animals. The classic example is ascorbic acid, which is not a vitamin in most animals. Humans do not exhibit specific defi-... 

Finally, there is only one well-documented species difference in the intestinal and bone response to vitamin D compounds. All C-24-substituted vitamin D compounds, e. g. all D2-derivatives and the 24-hydroxy-D3 analogs, are significantly less effective in birds than in other animals. This difference is believed to be caused by the more rapid degradation and excretion of D2 metabolites and 244iydroxy-D3... 

Many remarkable species differences have been found among the coenzymes. Most plants and animals synthesize their own ascorbic acid which is (among other tasks) essential for the hydroxylation of proline and lysine in the biosynthesis of collagen. However, Man, other primates, and the guinea pig are notable exceptions, so that for them, and for them alone, it is a vitamin, and must be taken in with food. 

There is considerable variation in the distribution of the vitamin between lobes of the liver (Hoppner et aL, 1968 McLaren et aL, 1978) and sites within a lobe (Olson et al, 1979). This variation is greater in human than in animal livers (Olson et al, 1979), probably a reflection in animal studies of the relatively controlled conditions of the laboratory environment, but it may be a real species difference. By an appropriate sampling technique, however, a single sample may be useful for assessing vitamin A status. Samples taken from the central portion of the right lobe are reported not to be significantly different from the overall... 

Rundles and Brewer (1958) have shown that methionine aggrevates bone marrow megaloblastosis and its addition to bone marrow cultures from vitamin deficient patients does not alleviate defective DNA synthesis (Waxman, 1969 Metz, 1968). This antifolate" effect of methionine in bone marrow cultures is in contrast to the "pro-folate effect described in rat liver. A species difference s not involved because similar results were found in rat bone marrow cultures (Cheng et al., 1975) leading to the hypothesis that methionine exerts its primary effect as an end-product inhibitor of the homocysteinetransmethylase reaction rather than regulation (via SAM) of 5 10 methylene THF reductase. It is also possible that the tissue culture system used to study bone marrow metabolism does not reflect the normal cellular environment. As Krebs et al. (1976) have pointed out, isolated normal hepatocytes have lost low molecular weight constituents including methionine and are incapable of some reactions known to occur in vivo. 

The gradual resolution of the vitamin B complex has introduced a new concept into nutrition namely, the existence of species differences in the growth requirements of higher animals. Thus, Bj is necessary for birds and mammals Bg and Bg are necessary for mammals, while Bg is necessary only for birds. 

Mobilization and Metabolism. The total ascorbic acid body pool in healthy adults has been estimated to be approximately 1.5 g, which increases to 2.3—2.8 g with intakes of 200 mg/d (151—158). Depletion of the body pool to 600 mg initiates physiological changes, and signs of clinical scurvy are reported when the body pool falls below 300 mg (149). Approximately 3—4% of the body pool turns over daily, representing 40—60 mg/d of metabolized, or consumed, vitamin C. Smokers have a higher metaboHc turnover rate of vitamin C (approximately 100 mg/d) and a lower body pool than nonsmokers, unless compensated through increased daily intakes of vitamin C (159). The metaboHsm of ascorbic acid varies among different species. 

The symptoms of vitamin E deficiency in animals are numerous and vary from species to species (13). Although the deficiency of the vitamin can affect different tissue types such as reproductive, gastrointestinal, vascular, neural, hepatic, and optic in a variety of species such as pigs, rats, mice, dogs, cats, chickens, turkeys, monkeys, and sheep, it is generally found that necrotizing myopathy is relatively common to most species. In humans, vitamin E deficiency can result from poor fat absorption in adults and children. Infants, especially those with low birth weights, typically have a vitamin E deficiency which can easily be corrected by supplements. This deficiency can lead to symptoms such as hemolytic anemia, reduction in red blood cell lifetimes, retinopathy, and neuromuscular disorders. 

The elemental and vitamin compositions of some representative yeasts are Hsted in Table 1. The principal carbon and energy sources for yeasts are carbohydrates (usually sugars), alcohols, and organic acids, as weU as a few other specific hydrocarbons. Nitrogen is usually suppHed as ammonia, urea, amino acids or oligopeptides. The main essential mineral elements are phosphoms (suppHed as phosphoric acid), and potassium, with smaller amounts of magnesium and trace amounts of copper, zinc, and iron. These requirements are characteristic of all yeasts. The vitamin requirements, however, differ among species. Eor laboratory and many industrial cultures, a commercial yeast extract contains all the required nutrients (see also Mineral nutrients). 

The third primary intermediate in the oxidation chemistry of a-tocopherol, and the central species in this chapter, is the orr/zo-quinone methide 3. In contrast to the other two primary intermediates 2 and 4, it can be formed by quite different ways (Fig. 6.4), which already might be taken as an indication of the importance of this intermediate in vitamin E chemistry. o-QM 3 is formed, as mentioned above, from chromanoxylium cation 4 by proton loss at C-5a, or by a further single-electron oxidation step from radical 2 with concomitant proton loss from C-5a. Its most prominent and most frequently employed formation way is the direct generation from a-tocopherol by two-electron oxidation in inert media. Although in aqueous or protic media, initial... 

Important intrinsic quality criteria currently determining the market potential of new apple cultivars are related to the sensory quality such as fruit firmness (crispness) and the sugar and acidity contents. On the other hand, the nutritional composition (e.g. the vitamin or antioxidant contents) is currently not used as a criterion in the choice of cultivars, neither in conventional nor in organic fruit production. The difference in the content of such components between fruit species is in most cases more relevant than between cultivars of the same species (e.g. vitamin C content of oranges versus apples). 

ABC transporters involved in the uptake of siderophores, haem, and vitamin B]2 are widely conserved in bacteria and Archaea (see Figure 10). Very few species lack representatives of the siderophore family transporters. These species are mainly intracellular parasites whose metabolism is closely coupled to the metabolism of their hosts (e.g. mycoplasma), or bacteria with no need for iron (e.g. lactobacilli). In many cases, several systems of this transporter family can be detected in a single species, thus allowing the use of structurally different chelators. Most systems were exclusively identified by sequence data analysis, some were biochemically characterised, and their substrate specificity was determined. However, only very few systems have been studied in detail. At present, the best-characterised ABC transporters of this type are the fhuBCD and the btuCDF systems of E. coli, which might serve as model systems of the siderophore family. Therefore, in the following sections, this report will mainly focus on the components that mediate ferric hydroxamate uptake (fhu) and vitamin B12 uptake (htu). 

Since in mammalian species metals first need to be assimilated from dietary sources in the intestinal tract and subsequently transported to the cells of the different organs of the body through the bloodstream, we will restrict ourselves in this section to the transport of metal ions across the enterocytes of the upper part of the small intestine (essentially the duodenum), where essentially all of the uptake of dietary constituents, whether they be metal ions, carbohydrates, fats, amino acids, vitamins, etc., takes place. We will then briefly review the mechanisms by which metal ions are transported across the plasma membrane of mammalian cells and enter the cytoplasm, as we did for bacteria, fungi and plants. The specific molecules involved in extracellular metal ion transport in the circulation will be dealt with in Chapter 8. 

It is well known that the protein content of milk from different species varies and is inversely related to the period of development of the young. The content of the B vitamins is likewise much higher in the milks of small, rapidly maturing animals63 than in human or cow s milk. There can be no serious doubt that the ability to produce milk at all, and also the composition of milk, is controlled to a large extent by genetic factors. On this basis one would expect that milk would vary in composition from individual to individual. 

By inhalative application of vitamin A, an accumulation of peripheral vifamin A stores is achieved. For the Irmg and the respiratory epithelium, concentrations in the range of 1-20 (ig/g were obtained (Biesalski, 1990). Looking at quantitative concentrations in the respiratory epithelium and in the mixed epithelium of the nasal mucosa yielded an accumulation of vifamin A — after topical administration in different animal species — in the epithelium of the nose increased by factor 10-100 (in human of factor 5-20) compared to the concentrations of the respiratory mucosa (Lewis, 1973). 

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