Chemistry Reference
In-Depth Information
1 month (Bougle et al., 1988). In addition, a study found that human milk
contained 1.42 mg/l at 42-60 d postpartum and 1.78 mg/l at 293 d (Rossipal
and Krachler, 1998). The FNB (Food and Nutrition Board: Institute of
Medicine, 2001) used an average value of 2 mg molybdenum/l of human
milk to calculate the AI for infants aged 0-6 months. The concentration of
molybdenum is much higher in bovine milk and humanized infant formulae,
which reports indicate ranges from 50 to 100 mg/l (Archibald, 1958; Tsongas
et al., 1980; Hunt and Meacham, 2001). The concentration in milk can be
increased substantially by ammonium molybdate supplementation (Archi-
bald, 1951). Much of the molybdenum in human (Zeise and Zikakis, 1987)
and bovine (Hart et al., 1967) milks is associated with xanthine oxidase.
Xanthine oxidase activity of human colostrum is about 10% that of bovine
milk (Oliver et al., 1971). Milk and milk products are considered rich sources
of molybdenum for humans (Nielsen, 2006).
10.13.
Cobalt
The only known function of cobalt in humans relates to its role in the
structure of the cobalamins, a group of cobalt-containing compounds (cor-
rinoids) (Stabler, 2006). The cobolamins are required as a co-factor for only
two, but very important, enzymes in humans:
L
-methylmalonyl CoA mutase
and methionine synthase. Only microorganisms retain the ability to synthe-
size cobalamins such that the source of cobalamins in all higher animals is
the product of microbial synthesis. Characteristic of these compounds,
cobalt is the central metal ion with four of the six coordination sites pro-
vided by a corrin ring (similar to the porphyrin ring found in heme). The
fifth cobalt coordination site is through 5,6-dimethylbenzimidazole but the
sixth coordination site, the center of reactivity, is variable: cyano, hydroxyl,
glutathione or coenzyme forms (methyl or adenosyl). Thus, cyanocobala-
min (the scientific term for ''vitamin B
12
'') can be converted to either of the
two cobalamin coenzymes that are active in human metabolism: methylco-
balamin and 5-deoxyadenosylcobalamin. Ironically, cyanocobalamin is an
artifact formed as a result of the use of cyanide in the purification proce-
dures. Furthermore, cyanocobalamin, compared to hydroxocobalamin,
binds to serum proteins less well and is excreted more rapidly (Tudhope
et al., 1967).
Unless cobalt is absorbed as an integral part of vitamin B
12
, the amount
of cobalt in milk or other foods is not relevant per se. However, B
12
deficiency
is a serious problem in human populations and is caused either by an inade-
quate dietary intake of vitamin B
12
or by malabsorption (e.g., lack of intrinsic
