Vitamin iron metabolism

Whilst these acids are of minor importance in man, another multifunctional acid, ascorbic add (vitamin C 6), has an apparent role in human iron metabolism as one of the postulated factors aiding iron uptake. Ascorbic add reduces Fe111 to Fe" with probable complexation of the latter. It thus converts Fe"1 to a more soluble form. Ascorbic acid can also reduce Cu" to Cu1 (equation 1), and there is accumulating evidence of a link between the metabolism of ascorbic acid and that of Cu.34... 

Antibiotics. Long-term administration of antibiotics could lead to vitamin B6 deficiency, If symptoms of peripheral neuropathy develop (numbness and tingling of the extremities), administer vitamin B6. Sulfasalazine can decrease the absorption of folic acid, and trimethoprim can cause folate deficiency, hence the need to administer folic acid if there is evidence of deficiency. Rifampicin can cause disturbances in vitamin D metabolism and lead to osteomalacia. The absorption of tetracyclines can be reduced by calcium, magnesium, iron and zinc, while this antibiotic could also decrease the absorption of these minerals. This effect is probably least with minocycline and is not confirmed with doxycycline. Doses of minerals and antibiotic should be separated by at least 2 hours. The absorption of quinolones is reduced by cationic and anionic supplements. 

In addition to the role of flavoproteins in iron metabolism, it is possible that the anemia associated with riboflavin deficiency is a consequence of the impairment of vitamin Be metabolism in riboflavin deficiency. Pyridoxine oxidase is a flavoprotein and, like glutathione reductase, is very sensitive to riboflavin depletion (McCormick, 1989). Vitamin Be deficiency can result in hypochromic anemia as a result of impaired porphyrin synthesis. Although riboflavin depletion decreases the oxidation of dietary vitamin Be to pyridoxal (Section 9.2), it is not clear to what extent there is secondary vitamin Be deficiency in riboflavin deficiency This is partly because vitamin Be nutritional status is commonly... 

The next three P450s (24A1, 27A1, 27B1) are involved in vitamin D metabolism (Figure 10.16). All three are mitochrondrial and receive electrons from the iron sulfur protein adrenodoxin (via the flavoprotein adrenodoxin reductase) (Table 10.1). 

INTERRELATIONSHIPS. Copper, along with certain vitamins, is involved in iron metabolism. 

Susceptibility to lead toxicity is influenced by dietary levels of calcium, iron, phosphorus, vitamins A and D, dietary protein, and alcohol (Calabrese 1978). Low dietary ingestion of calcium or iron increased the predisposition to lead toxicity in animals (Barton et al. 1978a Carpenter 1982 Hashmi et al. 1989a Six and Goyer 1972 Waxman and Rabinowitz 1966). Iron deficiency combined with lead exposure acts synergistically to impair heme synthesis and cell metabolism (Waxman and Rabinowitz 1966). 

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). 

The next five transition metals iron, cobalt, nickel, copper and zinc are of undisputed importance in the living world, as we know it. The multiple roles that iron can play will be presented in more detail later in Chapter 13, but we can already point out that, with very few exceptions, iron is essential for almost all living organisms, most probably because of its role in forming the amino acid radicals required for the conversion of ribonucleotides to deoxyribonucleotides in the Fe-dependent ribonucleotide reductases. In those organisms, such as Lactobacilli6, which do not have access to iron, their ribonucleotide reductases use a cobalt-based cofactor, related to vitamin B12. Cobalt is also used in a number of other enzymes, some of which catalyse complex isomerization reactions. Like cobalt, nickel appears to be much more extensively utilized by anaerobic bacteria, in reactions involving chemicals such as CH4, CO and H2, the metabolism of which was important... 

All quinolones interact with multivalent cations, forming chelation complexes resulting in reduced absorption. Major offenders are antacids vitamins containing calcium and iron can also be problematic. All fluoroquinolones interact with warfarin, didanosine (ddi), and phenytoin, resulting in decreased absorption or metabolism. Ciprofloxacin and other second-generation drugs interact with theophylline by decreasing its clearance, which leads to theophylline toxicity. 

As noted, vitamin C is needed for the production of collagen in the body, but it is also essential in the production of certain hormones such as dopamine and adrenaline. Ascorbic acid is also essential in the metabolism of some amino acids. It helps protect cells from free radical damage, helps iron absorption, and is essential for many metabolic processes. The dietary need of vitamin C is not clearly established, but the U.S. National Academy of Science has established a recommended dietary allowance (RDA) of 60 mg per day. Some groups and individuals, notably Linus Pauling in the 1980s, recommend dosages as high as... 

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