Biochemical processes, zinc

Trace elements are essential cofactors for numerous biochemical processes. Trace elements that are added routinely to PN include zinc, selenium, copper, manganese, and chromium. There are various commercial parenteral trace element formulations that can be added to PN admixtures (e.g., MTE-5 ). Zinc is important for wound healing, and patients with high-output fistulas, diarrhea, burns, and large open wounds may require additional zinc supplementation. Patients may lose as much as 12 to 17 mg zinc per liter of gastrointestinal (GI) output (e.g., from diarrhea or enterocutaneous fistula losses) however, others have demonstrated that 12 mg/day may be adequate to maintain these patients in positive zinc balance.18 Patients with chronic diarrhea, malabsorption, and short-gut syndrome may have increased selenium losses and may require additional selenium supplementation. Patients with severe cholestasis should have copper and manganese... 

Methodology of Zinc Determinations and the Role of Zinc in Biochemical Processes... 

In natural processes, metal ions are often in high oxidation states (2 or 3), whereas in chemical systems the metals are in low oxidation states (0 or 1). This fact inverts the role of the metal center, such that it acts as a one-electron sink in a natural system, but as a nucleophile in an artificial ones (see other chapters of this book and the review by Aresta et al. [109]). Nevertheless, important biochemical processes such as the reversible enzymatic hydration of C02, or the formation of metal carbamates, may serve as natural models for many synthetic purposes. Starting from the properties of carbonic anhydrase (a zinc metalloenzyme that performs the activation of C02), Schenk et al. proposed a review [110] of perspectives to build biomimetic chemical catalysts by means of high-level DFT or ah initio calculations for both the gas phase and in the condensed state. The fixation of C02 by Zn(II) complexes to undergo the hydration of C02 (Figure 4.17) the use of Cr, Co, or Zn complexes as catalysts for the coordination-insertion reaction of C02 with epoxides and the theoretical aspects of carbamate synthesis, especially for the formation of Mg2+ and Li+ carbamates, are discussed in the review of Schenk... 

We shall be concerned here only with zinc, since cadmium and mercury have, so far as is known, toxicity as their only biochemical function. Zinc, however, is one of the preeminently important metals in life processes, along with iron and copper. 

It appears that cobalt plays a particularly important role in the growth of cyanobacteria (Saito et al, 2002 Sunda and Huntsman, 1995b). Both Prochlorococcus and Synechococcus show an absolute cobalt requirement that zinc cannot substitute for (Figure 18(a)). The growth rate of Synechococcus is little affected by low zinc concentrations, except in the presence of cadmium which then becomes extremely toxic (Saito et al, personal communication). The biochemical processes responsible for the major cellular utilization of zinc and cobalt in marine cyanobacteria are unknown, however. These metals may be involved in carbonic anhydrase and/or other hydrolytic enzymes. Cobalamin (vitamin B12) synthesis is a function of cobalt in these organisms, yet B12 quotas tend to be very small (on the order of only 0.01 p.mol (mol C) ) and hence are not likely represent a significant portion of the cellular cobalt (Wilhelm and Trick, 1995). 

Recent laser excitation flow cytofluorometry of the dynamics of DNA metabolism in the cell cycle in zinc-deficient E. gracilis leave no doubt of the involvement of zinc in cell replication (13). The data demonstrate that all of the biochemical processes essential for cells to pass from Gi into S to G2 and from G2 to mitosis require zinc, and its deficiency can block all phases of the growth cycle of this organism. 

A deficiency of zinc in . gracilis has been shown to affect adversely all the phases of cell cycle (Gi, S, G2, and mitosis), thus indicating that zinc is required for biochemical processes essential for cells to pass from G2 to mitosis, from S to G2, and from Gi to S (13). The effect of zinc on cell cycle is undoubtedly attributable to its vital role in DNA synthesis (90,9i). Many studies have shown that zinc deficiency in animals im-... 

Applications technologies in metal ion, inorganic species, hydrocarbons separations, biochemical and biomedical applications, and fine particles preparation using ELM are reviewed. Commercial applications include the removal of zinc, phenol, and cyanide from wastewaters. Potential applications in wastewater treatment, biochemical processing, rare earth metal extraction, radioactive material removal, and nickel recovery are described. 

Copper is an essential element for plant growth and important in various biochemical process, but toxic in higher concentrations, when it interferes with numerous physiological processes. While manganese, iron and zinc are essential microelements that are indispensable for normal plant growth... 

Further reading Mikac-Devic, D. (1970). Methodology of zinc determinations and the role of zinc in biochemical processes. In Bodansky, O. and Stewart, C.P. (eds.) Advances in Clinical Chemistry. Vol. 13, p. 271. (New York Academic Press)... 

One of the most important metals with regard to its role in enzyme chemistry is zinc. There are several significant enzymes that contain the metal, among which are carboxypeptidase A and B, alkaline phosphatase, alcohol dehydrogenase, aldolase, and carbonic anhydrase. Although most of these enzymes are involved in catalyzing biochemical reactions, carbonic anhydrase is involved in a process that is inorganic in nature. That reaction can be shown as... 

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