Window of essentiality

In any case, such values of electrochemical parameters for ligands relevant in biology almost from biopoiesis onwards allowed for broad and differentiated use of now essential elements much like in recent biomasses also >2.3 bio. years ago, without the necessity to have specialized transport systems at hand. Possibly, phosphate-containing regulating systems and transporters - besides the more advanced polyphenols, hydroxamates or proteins (chaperons) - involved in transportation of, e.g. Fe are relics of those days. Possible items of such transport include all of the more general essential elements except for Co and V. The edges to the central window of essentiality in the c/x... 

Fig. 2.20 Formal fitness landscape of various biocatalytic and inactive (i.e., the latter being located outside the window of essentiality ) metal ions for the carboxypeptidase A (Vallee and Williams 1968). The enzyme reconstituted by cobalt (treatment with EDTA, then addition of Co +) is considerably more active than the native Zn version , while Cd (and other ions) afford poorly to non-active metalloproteins in this case. (Relative) catalytic turnover rates are from Vallee and Williams 1968, x and c values this work and previous publications by this author. Here, sufficient abundance of the corresponding ions is taken for granted owing to in-vitro addition to apoprotein, so c k is not hmited by c, but merely represents the catalytic features pertinent to k, obtained from either biochemistry (several metal ions being present, e.g. in phosphatases) or experiments with reconstituted apoproteins...

Ba must get recovered from specific resources (food, soil solution or ambient waters) also, which is not trivial given that bond stability (Ba complexes are very weak as a rule) and ligand selectivity differ considerably (both c and X to the negative) from those elements forming the window of essentiality . 

In redox-active elements like those fisted above, parameters c and x depend on the ambient redox potential including changes of ambient (geobio-chemical) conditions, causing moves in or around the window of essentiality , unlike with, say, Mg, Ca, Zn or Cd. 

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