Metals in the living cell

and other vertebrates, require cations of the following metals to facilitate a great many essential life processes. Moreover, many of these metals are essential for all other forms of life  

In 1935, two groups of workers in Australia found that the vast, lush pastures that produced severe anaemia in sheep in that country and New 

Zealand, did so through lack of cobalt, an element which is not required by plants. When the cobalt content of grass was less than 0.2 of a part per million, the sheep became weak and died. This debility was traced to a failure of microflora in the sheep s rumen to synthesize the cobalt-containing coenzymes (Marston, Allen and Smith, 1961). Addition of cobalt to the sheep s diet is now used to prevent this condition, and the productivity of the land has increased almost unbelievably. 

In the human, as little as one microgram of vitamin (intramuscularly) is sufficient daily therapy for pernicious anaemia. In a man weighing 70 kg, this represents only 0.000002 p.p.m. of his weight. 

Copper is an essential constituent of many enzymes. The effects of traces of copper on oat-seedlings, grown in a copper-deficient medium, is shown in Plate 5 (p. 395). Plainly, too little copper is bad for growth, and so is too much. Until recognized as such, copper-deficiency was the cause of many a crop failure in the reclaimed areas of Holland and Denmark. Copper-deficiency in farm animals leads to anaemia, demyelination of the spinal cord, and loss of pigmentation. Excessive copper-storage in the liver of sheep leads to haemolysis and death (Albiston, et aL 1940). 

The green-coloured enzyme superoxide dismutase, present in every tissue of eukaryotes, contains both copper and iron linked to the same imidazole nucleus (His-61) in the apoenzyme. The copper undergoes a cycle of oxidation and reduction as it destroys toxic superoxide radicals ( 02 ) which arise from reactions using atmospheric oxygen. 

In the superoxide dismutase of bovine erythrocytes, and possibly elsewhere, zinc and copper are both linked to a histidine moiety. Analogous enzymes containing manganese instead of copper occur in both mammalian and bacterial organisms (Oberley and Buettner, 1979). For further reading on this highly unusual metalloenzyme, see Oberley (1982) and Rodgers and Powers (1981). 

---

Oxidation-reduction reactions similar to the Cannizzaro process are brought about in the living cell by certain enzyme systems. Numerous exanfples 7-8- 10 of these have been studied in vitro by the aid of tissue preparations, and certain of them 6 suggest possible application in preparative methods. The dismutation. of aldehydes in basic or neutral solution also has been effected by catalytic metals, such as nickel and platinum.11 12 It seems likely that there is a closer analogy between... 

Having obtained the protein, how do we know if it is pure A lot depends on exactly what we mean by pure in this context, in the early days of protein chemistry a lot of attention was paid to ridding the protein of all traces of non-protein materials, such as metal ions or fragments of lipid or carbohydrate. But it is now clear that in the living cell itself much extraneous material occurs bound into extremely close association with the protein. To remove it, even when this can be done, may produce a satisfactorily chemically pure amino acid chain, but that is not really what one is after the important thing is to isolate as close an approximation to the native material as possible - even if this does mean taking it with its warts and all. 

The action of ascorbic acid on many enzymes appears to be conditioned by other substances, notably metallic ions, present in reaction mixtures certainly where its action has been critically examined, this has been found to be so. Whether ascorbic acid in vivio has any regulatory influence on these enzymes is uncertain. Still more improbable is the view that this action of ascorbic acid constitutes one of its essential roles in the living cell, since it has been shown both for j3-amylase and urease that other dienols (reductone, dehydroxymaleic acid, reductic acid, hydroxy-tetronic acid) which are biologically inactive react similarly (Hanes, 1935 Mapson, 1946). 

In the soil diazotrophic rhizobacterium A. brasilense (strain Sp245, reported to be tolerant to submillimolar concentrations of heavy metals, including cobalt(ll), in the culture medium [32]), EMS studies were first performed on freeze-dried bacterial samples (measured at T = 80K Fig. 17.2) [27]. The following experiments with the same bacteria were performed with live cells rapidly frozen after certain periods of time (2-60 min) of contact with Co", and EMS spectra were measured for frozen suspensions (without drying), which more closely represent the state of cobalt in the live cells [31,32] (Fig. 17.3). Mossbauer parameters calculated from the experimental data are listed in Table 17.1. 

Biosorption is a process where metal ions (or metalloid species), compoimds and particulate substances are removed from solution by biological material through adsorption of the contaminant on a surface site of the biomass. It can be by physical forces (e.g. van der Waals, electrostatic interaction) and/or involving a chemical reaction. It is believed that biosorption using dead biomass is based on the physical sorption phenomenon, whereas sorption using live biomass occurs through both physical and chemical processes as well as transmembrane transport and accumulation of heavy metals in the algal cell. ... 

The metallic substrate, clean and rinsed, is immersed wet in the plating cell. The base metals which are usually plated present an essentially metallic surface to the electrolyte, and the slight corrosive action of the rinse water in preventing the formation of any substantial oxide film is important. A critical balance of corrosion processes in the initial stages is vital to successful electroplating, and for this reason there is a severe restriction on the composition of the electroplating bath which may be used for a particular substrate. This will be discussed later. The substrate is made the cathode of the cell it may be immersed without applied potential ( dead entry) or may be already part of a circuit which is completed as soon as the substrate touches the electrolyte ( live entry). Live entry reduces the tendency for the plating electrolyte to corrode the substrate in the period before the surface... 

Many important questions can be asked about the binding of metal ions within living cells. For example, What fraction of a given metal ion is free and what fraction is bound to organic molecules To what ligands is a metal bound Since many metal ions are toxic in excess, it is clear that homeostatic mechanisms must exist. How do such mechanisms sense the free metal ion activity within cells How does the body get rid of unwanted metal ions Answers to all these questions depend upon the quantitative differences in the binding of metal ions to the variety of potential binding sites found within a cell. 

In Aphorisms, Hippocrates asserted that diseases which are not healed by cures, are healed by iron . We know now that iron is distributed in all of the living organisms and that all of the cells need iron to survive and to grow. For this reason. Nature has coined the transferrins of which the mission is to furnish this invaluable metal to all living cells (for a review, see ref. [7]). 

Calcium is essential to all living things. Calcium compounds are a vital component of the skeletons and bones of mammals, amphibians, reptiles, birds, fish, and other land and marine animals. The most abundant metal in the human body, calcium makes up the bones and serves other functions in the body s metabolic system. These functions include keeping cells joined together, aiding in muscle contraction and conduction of nerve impulses, helping blood clot, and controlling cell division. 

Six nonmetallic major bioelements or macroelements are needed to form the multitude of macromolecules in a living cell (C, O, H, N, P, S), and four additional metals to neutralize the predominantly negative charges of these macromolecules (K, Mg, Ca, Na). While the elements from carbon to calcium are undisputed major bioelements, some authors may remove sodium (Na) from this list and insert iron (Fe) instead. However, iron - like most trace elements - is a transition element, whereas sodium is an element of a major group of the periodic system like the other three metallic major bioelements. 

Heavy metals, in traces, are essential for all forms of life. They are taken up by the living cell as cations, and their uptake is strictly regulated because most (or all) of them are toxic in excess. A remarkable specificity has been found seldom can an excess of one essential metal prevent the damage caused by a deficiency of another. In fact, such an excess often increases the injurious effect of the deficiency. 

Apart from amino acids, peptides and proteins, many other metal-binding substances play essential roles in all living cells. Firstly, there are the pteridines (including folic acid) and purines, whose stability constants have been determined (Albert, 1953 Albert and Serjeant, 1960). Riboflavine is most avid in the partly reduced state (Hemmerich, Veeger and Wood, 1965). Spermine 11 A), and the diamines spermidine 11.5) and putrescine 11.6) also compete. 

Iron, Fe a bioelement found in all living cells. The human body contains 4-5 g Fe, of which 75 % is in hemoglobin. In living organisms Fe occurs in the II and III oxidation states in higher animals it is stored bound to protein. It is transported in the blood as a complex with transferrin (see Siderophilins), from which it is transferred enzymatically to metal-ffee porphyrin molecules (see Heme iron). Non-heme iron (see) is also found in a number of compounds, e.g. Iron-sulfur proteins (see). The Fe metabolism of microorganisms is mediated by a group of natural products called Siderochromes (see). 

---