Se is present in ~25 human proteins (selenoproteins) as a constituent of the amino acid selenocysteine, which is derived from serine (see p. 268). Selenoproteins include glutathione peroxidase that oxidizes glutathione in the reduction of hydrogen peroxide, a ROS, to water (see p. 148); thioredoxin reductase that reduces thioredoxin, a coenzyme of ribonucleotide reductase (see p. 297); and deiodinases that remove I from thyroid hormones. Meat, dairy products, and grains are important dietary sources. Keshan disease, first identified in China, is a cardiomyopathy caused by eating foods produced from Se-deficient soil. Toxicity (selenosis) caused by overingestion of supplements causes brittle nails and hair. Cutaneous and neurologic effects may also be seen (UL = 400 µg in adults).
C. Molybdenum
Mo functions as a cofactor for a small number of mammalian oxidases (Fig. 29.17). Legumes are important dietary sources. No dietary deficiency syndromes are known. Mo has low toxicity in humans (UL = 2 mg/day in adults).
Cobalt (Co), an ultratrace mineral, is a component of vitamin B12 (cobalamin, see p. 379), which is required as methylcobalamin in the remethylation of homocysteine to methionine (see p. 264) or adenosylcobalamin in the isomerization of methylmalonyl coenzyme A (CoA) to succinyl CoA (see p. 194). No Recommended Dietary Allowance or Daily Reference Intake (see p. 358) has been established for Co.
V. CHAPTER SUMMARY
The minerals are summarized in Figure 29.18 on p. 408.
For Questions 29.1–29.7, match the mineral to the most appropriate description.
A. Calcium
B. Chloride
C. Copper
D. Iodine
E. Iron
F. Magnesium
G. Manganese
H. Molybdenum
I. Phosphorus
J. Potassium
K. Selenium
L. Sodium
M. Zinc 9.1. Elevated levels of which mineral may result in hypertension in certain populations?
9.2. Which mineral is the major extracellular anion?
9.3. A decrease of which mineral is seen in refeeding syndrome and with overuse of aluminum-containing antacids?
9.4. Which mineral is a constituent of some amino acids found in proteins involved in antioxidant defense, thyroid hormone metabolism, and redox reactions?
9.5. Which mineral is required for the formation of a supersecondary protein structure that allows binding to DNA? (Its deficiency can result in a dermatitis.) 9.6. Deficiency of which mineral can cause bone pain, tetany (intermittent muscle spasms), paresthesia (a “pins and needles” sensation), and an increased tendency to bleed?
9.7. Deficiency of which mineral can result in goiter and a decreased metabolic rate?