Zinc and Calcium

In thermolysin (Matthews et al., 1974 Holmes and Matthews, 1982) zinc is bound approximately tetrahedrally to glutamate (monodentate), two histidines, and water. While zinc in the native enzyme is tetracoord-inate, in some inhibitor complexes it is pentacoordinate. The four calcium ions are bound by six to eight oxygen ligands, as shown in Fig. 35, with Ca 0 distances of 2.23-2.71 A. The RNA polymerase from E. coli contains Zn(II) and Mg(II), which may be substituted by Mn(II) (Chuk-nyhVy et al., 1990). 

---

Zinc and calcium siUcates, and calcium tungstate doped with activators such an Mn, Pb, Sn, and Eu are just a few examples of a large number of known ionicaHy bonded luminescent pigments. HaUde phosphates of the general formula 3Ca(P0 2 CaX2, where X = F or Cl, and Sb " and are... 

Many stabilizers require costabilizers. Several organic costabilizers are quite useful with barium—zinc and calcium—zinc stabilizers, eg, P-diketones, epoxies, organophosphites, hindered phenols, and polyols (122). 

Vulcanisation may also be brought about by zinc and calcium peroxides, p-quinone dioxime, epoxide resins, phenolic resins and di-isocyanates. 

The plutonium reduces and separates from the salt phase. In the third step, distillation is used to separate the more volatile zinc and calcium from the plutonium. 

Zinc and cadmium have an oxidation number of +2 in all their compounds. Zinc is an essential element for human health. It is present in many enzymes and plays a role in the expression of DNA and in growth. Zinc is toxic only in very-high amounts. However, cadmium is a deadly poison that disrupts metabolism by-substituting for other essential metals in the body such as zinc and calcium, leading to soft bones and to kidney and lung disorders. 

Heat stabilisers for PVC act by HC1 scavenging and include organotins, mixed metal salt blends, and lead compounds. The latter account for nearly 64 % of volume (in 1994), followed by barium/cadmium and organotin compounds. Cadmium-based heat stabilisers are rapidly being replaced due to environmental concerns. Barium/zinc and calcium/zinc compounds show a high growth rate. It is expected that methyltin stabilisers will soon dominate the growing PVC pipe market. 

The matrix metalloendoproteinases (MMPs or matrixins) are a family of zinc and calcium dependent extracellular proteases that collectively degrade most of the protein constituents of the extracellular matrix [9]. There are at least 23 members of this family and are divided primarily on the basis of sequence homology and substrate specificity into the following grouping collagenases (MMP-1, -8, -13, -18) gelatinases... 

The variety of prebiotic organic reactions seems to be almost unlimited. Strasdeit et al. (2002) from the University of Hohenheim (Germany) reported the synthesis of zinc and calcium complexes of the amino acids valine and isovaline. They assume that these could have had a certain significance on the mineral-rich primeval Earth on heating to 593 K under nitrogen, valine was converted to the corresponding cyclic dipeptide. 

Morgan, J.E. and A.J. Morgan. 1990. The distribution of cadmium, copper, lead, zinc and calcium in the tissues of the earthworm Lumbricus rubellus sampled from one uncontaminated and four polluted soils. Oecologia 84 559-566. 

Redo, A., J.A. Marigomez, E. Angulo, and J. Moya. 1988a. Zinc treatment of the digestive gland of the slug Arion ater L. 1. Cellular distribution of zinc and calcium. Bull. Environ. Contam. Toxicol. 41 858-864. 

The rat has been used rather widely to study the relation between dietary protein, or acid salt feeding, and calcium loss. Barzel and Jowsey (19) showed that the rat fed a control diet supplemented with ammonium chloride excreted excessive urinary calcium, and experienced a concomitant loss of fat-free bone tissue. Draper, et al. (20) extending this work, reported an inverse relation between dietary phosphate and loss of bone calcium and dry, fat-free tissue. In subsequent studies (21), they reported that this process was accompanied by reduced serum calcium levels the high phosphorus, low calcium diet increased urinary calcium loss. Whereas, increasing the phosphorus content of the diet stopped the excessive urinary calcium loss. To test possible zinc loss that might result from this sort of acid salt feeding, Jacob and her coworkers (22) fed rats a supplement of ammonium chloride and then measured urinary zinc and calcium. The hypercalciuria occurred exclusive of an effect upon urinary zinc loss. 

Matrix metalloproteinases (MMPs) are a class of zinc- and calcium-dependent enzymes that are responsible for the metabolism of extracellular matrix proteins [27]. Increased activity of MMPs has been associated with pathological diseases such as arthritis, cancer, multiple sclerosis and Alzheimer s disease [28-31]. Therefore, they constitute an important group of drug targets. Their inhibition is accomplished by blocking the active site of the catalytic domain with ligands that contain hydroxamic or carboxylic acids to chelate the Zn metal. The identification of low molecular weight compounds that contain different scaffolds may lead to the development of a new class of specific inhibitors. 

This zinc- and calcium-dependent enzyme [EC 3.4.24.36] catalyzes the hydrolysis of peptide bonds, exhibiting a preference for hydrophobic amino acid residues at positions PI and PL, and basic amino acid residues at P2 and P3. ... 

Bcla-pheiiylhydroxylaminc is formed by reduction of nitrobenzene 111 by zinc and calcium chloride or ammonium chloride solution. i2l by electrolysis in acetic acid plus sodium acetate solution. 

Zinc soaps, which are complexes of long chain fatty acids, find similar applications in the curing and hardening of coatings to other transition metal soaps. A summary is available.123 The more important anions are 2-ethylhexanoate, naphthenate and stearate. Mixtures of zinc and calcium soaps are also effective stabilizers for poly(vinyl chloride).124 The complexes [Zn 0P(0)-(OBun)2 2] and [Zn SP(S)(OBun)2 2] both promote antiwear properties of lubricating oils.125... 

The tribofilms formed from a ZDDP were composed of long chain phosphates with zinc as a cation but with a mixture of a ZDDP + detergent and ZDDP + dispersant, only short-chain phosphates with zinc and calcium as cations are formed in the presence of a sulfide (Barcroft and Park, 1986 Willermet et al., 1995a). 

Molybdenum salts used as catalysts include cobalt molybdate for hydrogen treatment of petroleum stocks for desulfurization, and phospho-molybdates to promote oxidation. Compounds used for dyes are sodium, potassium, and ammonium molybdates. With basic dyes, phosphomolyb-dic acid is employed. The pigment known as molybdenum orange is a mixed crystal of lead chromate and lead molybdate. Sodium molybdate, or molybdic oxide, is added to fertilizers as a beneficial trace element. Zinc and calcium molybdate serve as inhibitory pigments in protective coatings arid paint for metals subjected to a corrosive atmosphere. Compounds used to produce better adherence of enamels are molybdenum trioxide and ammonium, sodium, calcium, barium, and lead molybdates. 

Hansen, M., Sandstrom, B., and Lonnerdal, B. 1996. The effect of casein phosphopeptides on zinc and calcium absorption from high phytate infant diets assessed in rat pups and caco-2 cells. Pediatr. Res. 40, 547-552. 

Hansen, M., Sandstrom, B., Jensen, M., and Sorensen, S.S. 1997. Casein phosphopeptides improve zinc and calcium absorption from rice-based but not from whole-grain infant cereal. J. Pediatr. Gastroenterol. Nutr. 24, 56—62. 

Thermolysin, originally derived from Bacillus thermoproteolyticus, can be categorized as a neutral metalloprotease. The optimum conditions for this enzyme are pH 7.0 and 60-80 °C. Thermolysin also requires catalytically active zinc,and calcium for thermostability (Whitaker, 1994). When these conditions are met, heat-stable thermolysin specifically hydrolyzes peptide bonds involving isoleucine, leucine, valine, and phenylalanine (Adler-Nissen, 1986). It has been extensively utilized in the production of antihypertensive peptides which will be discussed later in this review. 

The behavior of minerals is often influenced by the presence of other food constituents. The recent interest in the beneficial effect of dietary fiber has led to studies of the role fiber plays in the absorption of minerals. It has been shown (Toma and Curtis 1986) that mineral absorption is decreased by fiber. A study of the behavior of iron, zinc, and calcium showed that interactions occur with phytate, which is present in fiber. Phytates can form insoluble complexes with iron and zinc and may interfere with the... 

---