Metal ions biology

Kelley SO, Barton JK (1999) Metal Ions Biological Syst 36 211... 

Dhar, Sanat K. (1973). Metal Ions Biological System. New York Plenum. 

In addition to concentration of metal ions, biological materials and environmentally important organic compounds have also been... 

The first and primary protective effect of fluoride is due to its strong, spontaneous reaction with metal ions. Biologically, the most important of these ions is the calcium ion, large amounts of which interact with phosphate to form bones and teeth. Studies show that fluoride reduces apatite solubility in acids by an isomorphic replacement of hydroxide ions with fluoride ions to form fluoro-hydroxyapatite and difluoro-apatite (Fig. 16.6a). 

R 323 J. P. Andre and H. R. Macke, NMR Spectroscopy of Group 13 Metal Ions Biologically Relevant Aspects , J. Inorg. Biochem.,2003,91,315... 

The munber and chemical variety of vitamin coenzyme forms, and the instability of many of their reduced forms, have made it difficult to separate and quantify vitamins in complex mixtures. In general, crystalline water-soluble vitamins are relatively stable in the presence of air, whereas in solution some are easily oxidized. They are generally most stable in acidic media, and least stable in alkaline ones (Table 1). Their degradation in solution is further dependent on the temperature, the presence or absence of oxygen, and the presence or absence of metal ions. Biological... 

The red tetrathiomolybdate ion appears to be a principal participant in the biological Cu—Mo antagonism and is reactive toward other transition-metal ions to produce a wide variety of heteronuclear transition-metal sulfide complexes and clusters (13,14). For example, tetrathiomolybdate serves as a bidentate ligand for Co, forming Co(MoSTetrathiomolybdates and their mixed metal complexes are of interest as catalyst precursors for the hydrotreating of petroleum (qv) (15) and the hydroHquefaction of coal (see Coal conversion processes) (16). The intermediate forms MoOS Mo02S 2> MoO S have also been prepared (17). 

Because of the time and expense involved, biological assays are used primarily for research purposes. The first chemical method for assaying L-ascorbic acid was the titration with 2,6-dichlorophenolindophenol solution (76). This method is not appHcable in the presence of a variety of interfering substances, eg, reduced metal ions, sulfites, tannins, or colored dyes. This 2,6-dichlorophenolindophenol method and other chemical and physiochemical methods are based on the reducing character of L-ascorbic acid (77). Colorimetric reactions with metal ions as weU as other redox systems, eg, potassium hexacyanoferrate(III), methylene blue, chloramine, etc, have been used for the assay, but they are unspecific because of interferences from a large number of reducing substances contained in foods and natural products (78). These methods have been used extensively in fish research (79). A specific photometric method for the assay of vitamin C in biological samples is based on the oxidation of ascorbic acid to dehydroascorbic acid with 2,4-dinitrophenylhydrazine (80). In the microfluorometric method, ascorbic acid is oxidized to dehydroascorbic acid in the presence of charcoal. The oxidized form is reacted with o-phenylenediamine to produce a fluorescent compound that is detected with an excitation maximum of ca 350 nm and an emission maximum of ca 430 nm (81). 

MacrotetroHdes of the valinomycin group of electrically neutral antibiotics form stable 1 1 complexes with alkaH metal ions that increase the cation permeabiHty of some biological and artificial lipophilic membranes. This solubiHzation process appears to have implications in membrane transport research (30) (see Antibiotics, peptides). 

H. Siegel, ed.. Metal Ions in Biological Systems, Vol. 12, Properties of Copper, Marcel Dekker, New York, 1981, p. 384. 

Recent publications indicate the cloud-point extraction by phases of nonionic surfactant as an effective procedure for preconcentrating and separation of metal ions, organic pollutants and biologically active compounds. The effectiveness of the cloud-point extraction is due to its high selectivity and the possibility to obtain high coefficients of absolute preconcentrating while analyzing small volumes of the sample. Besides, the cloud-point extraction with non-ionic surfactants insures the low-cost, simple and accurate analytic procedures. 

Most biological environments contain substantial amounts of divalent and monovalent metal ions, including Mg, Ca, Na, K, and so on. What effect do metal ions have on the equilibrium constant for ATP hydrolysis and the... 

Tu, A. J., Heller, M. J. Structure and Stability of Metal-Nucleoside Phosphate Complexes, in Metal Ions in Biological Systems Vol. 1 (ed. Sigel, H.), p. 1, Marcel Dekker, Inc. New York 1974... 

Aldol reactions occur in many biological pathways, but are particularly important in carbohydrate metabolism, where enzymes called aldolases catalyze the addition of a ketone enolate ion to an aldehvde. Aldolases occur in all organisms and are of two types. Type 1 aldolases occur primarily in animals and higher plants type II aldolases occur primarily in fungi and bacteria. Both types catalyze the same kind of reaction, but type 1 aldolases operate place through an enamine, while type II aldolases require a metal ion (usually 7n2+) as Lewis acid and operate through an enolate ion. 

It should be noted that Cypridina luciferin emits a fairly strong chemiluminescence in aqueous solutions in the presence of various lipids and surfactants, even in the complete absence of luciferase. The luminescence is especially conspicuous with cationic surfactants (such as hexadecyltrimethylammonium bromide) and certain emulsion materials (such as egg yolk and mayonnaise). Certain metal ions (especially Fe2+) and peroxides can also cause luminescence of the luciferin. Therefore, great care must be taken in the detection of Cypridina luciferase in biological samples with Cypridina luciferin. 

Vitamin B12 (Fig. 1) is defined as a group of cobalt-containing conoids known as cobalamins. The common features of the vitamers are a corrin ting (four reduced pyrrole rings) with cobalt as the central atom, a nucleotide-like compound and a variable ligand. Vitamin B12 is exceptional in as far as it is the only vitamin containing a metal-ion. The vitamers present in biological systems are hydroxo-, aquo-, methyl-, and 5 -deoxyadenosylcobalamin. 

Interactions of histidine and other imidazole derivatives with transition metal ions in chemical and biological systems. R. J. Sundberg and R. B. Martin, Chem. Rev., 1974, 74, 471-517 (517). 

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