Polyphosphates, determination structure

Even before the above facts and structural considerations were generally appreciated by chemists, some of the polyphosphates, such as Graham s salt and the triphosphate, for example, had acquired major technical importance 90, 91,127,129, 249). About thirty years ago the study of condensed phosphates was taken up from many sides in attempts to determine their structures and, from their structures, to understand their properties. Preparative methods, physico-chemical investigations and theoretical considerations were all brought into play in order to develop this branch of inorganic chemistry to a point where, today, the perspective is clear and we can regard it as well-investigated. 

Perhaps the formation of trimetaphosphate and small quantities of tetrametaphosphate from dissolved polyphosphates, which can amount to 70% in presence of Mg++ ions, is an indication of the form in which the anion chains are present in the solution. In any case this formation of trimetaphosphates is not, contrary to what was proposed initially (293, 326), an argument for the assumption that trimetaphosphate rings constitute a structural unit in the polyphosphates. Thus in solutions of Maddrell s salt, the anions of which are known to be linear chains from crystal structure determination (78) (see Section IV,E,2), up to 50% yields of trimeta-... 

Tzeng, C.M. Kornberg, A. The multiple activities of polyphosphate kinase of Escherichia coli and their subunit structure determined by radiation target analysis. J. Biol. Chem., 275, 3977-3983 (2000)... 

Enzymatic activity, however, is not merely associated with covalent structures, but chiefly with tertiary structure which is still more difficult to determine. The crucial role of tertiary structure is proved by the fact that denaturation brings about inactivation. Even with proteins which may be reversibly denatured, such as chymotrypsin and trypsin, activity is lost as long as denaturation persists. Ribonuclease appeared for a while to be an exception, since it was still active in 8 M urea. But it was shown later that phosphate ions, at a concentration as low as 0.003 M, and polyphosphates induced in urea-denatured ribonuclease spectral changes usually associated with refolding (164). It could then be assumed that ribonucleic acid, the actual substrate, was also able to refold the denatured form and prevent inactivation in this way. In other words, even in ribonuclease, the active center is probably not built by adjacent residues in a tail or a ring, but by some residues correctly located in space by the superimposed... 

The crystal structure of recombinant bovine inositol polyphosphate 1-phosphatase (1-ptase) was determined in the presence of Mg + at 2.3-A resolution (York et al., 1994). The fold of 1-ptase is similar to that of two other metaI-dependent/Li+-sensitive phosphatases, inositol monophosphate phosphatase and fructose 1,6-biphosphatase. Comparison of the active-site pockets of these proteins will likely provide insight into substrate binding, the mechanisms of metal-dependent catalysis, and Li+ inhibition. 

Using the silver polyphosphates obtained by the above procedures, one can determine the chemical composition of the polyphosphates and thereby estimate the structure of a given sodium meta-arsenate-phosphate. Several methods can be used for this purpose (a) paper chromatographic analysis of the polyphosphates, (b) determination of Ag/P ratios of the silver polyphosphates, (c) titrimetric determination of weak acid hydrogen of the polyphosphates, (d) measurement of depression of transition points of sodium sulfate decahydrate by the addition of the polyphosphates, and (e) fractional precipitation of the polyphosphates with silver nitrate... 

Solvent structural factors seem to have little effect on activation parameters for aquation of [Co(DMSO)(NH3)5] + in ethanol-water mixtures, but are significant in polyphosphate hydrolysis (which is probably 5 n2) in dioxan-water and formic acid-water media. - Solvent structure is important in determining kinetic parameters for reaction of copper(n) with chlorophyllic acid in mixed non-aqueous media (see below). 

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