Phosphate Ion as a Promoter Catalyst of Respiration
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چکیده
In other papers (Lyon, 1923-24, 1927) results have been reported which appeared to show that neutral solutions of sodium or potassium phosphate serve to catalyze the enzymatic production of CO2 by plant tissues. The oxidising enzymes involved were those of Elodea canadensis, wheat seedlings, and potato tubers, the latter studied only in aqueous extracts. We shall now present additional proof of this promoter action through more careful analyses to determine the active component of mixtures of monoand disodium phosphates. The molar concentrations of the solutions which gave optimum resuits were somewhat high for the usual types of catalysis. The concentration most used was approximately 0.1 ~, by which is meant a solution obtained by mixing 0.1 ~r monosodium phosphate with 0.1 • r disodium phosphate. The complex nature of the components of such a solution suggested that some single element among them was the active, or at least the controlling factor of the catalysis. Since the ionization of even this concentration of the sodium phosphates is presumably complete, we are concerned primarily with the nature of the ionization products of phosphoric acid. An excellent statement of the conditions of equilibrium between H2PO', HPO,", and P04'" is given by Holt, La Mer, and Chown (19251), from which it is apparent that for HsPO~, Kx is very large, Ks is smaller, and Ks, which determines the relative amounts of PO~ "~, is very small. These authors have also calculated the concentrations of PO4 "~ in relation to pH over a wide range and have introduced the expression p[PO4"q which may
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Phosphate Ion as a Promoter Catalyst of Respiration
The active component of phosphate solutions, in relation to promoter action on oxidising enzymes, is the PO(4) (''') ion. This is shown by the demonstration of a hyperbolic relationship between per cent production of CO(2) (of Elodea) and pPO(4), the measure of the phosphate ion potential. This is consistent with the rate of respiration as affected by changing pPO(4) through change of total pho...
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تاریخ انتشار 2003