Phosphate, inorganic exchange reactions

The existence of the Ei, and E2 states of the phosphorylated protein, i.e., the high-and low-energy phosphoenzyme intermediate, has been demonstrated by the ATP ADP exchange reaction [92,93] and by the exchange between inorganic phosphate and water [94]. 

The oxidation to form acyl phosphates is reversible. Acyl groups may also be transferred by this enzyme. Acetyl groups are transferred from acetyl phosphate to the sulfhydryl groups of compounds such as glutathione and CoA acetyl phosphate is hydrolyzed in the presence of arsenate and the phosphate of acetyl phosphate is exchanged with inorganic phosphate (measured by labeling with These reactions... 

Polynucleotide phosphorylase can be assayed in several ways. The liberation of inorganic phosphate can be used to follow the reaction. Both disappearance of acid-soluble nucleotides and formation of acid-insoluble nucleotides have been measured. The reverse reaction in the presence of P Mabeled phosphate allows an exchange reaction, the incorporation of P into nucleotides, to be used as an assay. The exchange reaction was the first reaction of this enzyme to be discovered, and studies on the responsible enzyme led to the finding of polynucleotide synthesis. Another assay based on the reverse reaction has been devised for rapid spectrophoto-metric determinations. A polymer of adenylic acid is incubated with the phosphorylase in the presence of phosphate, phosphopyruvate, pyruvate kinase, DPNH, and lactic dehydrogenase. The formation of ADP is thus coupled with the formation of pyruvate which reacts stoichiometrically with PPNH, so that the entire reaction can be followed at 340 m/a. 

The transferase reaction requires catalytic amounts of ADP and inorganic phosphate as well as a metal. In this reaction Mn++ is more effective than Mg++. Cysteine or another —SH compound activates the transferase as well as the synthetase reaction. L-Glutamine is much more effective in the exchange reaction than the D-isomer, and analogs of glutamine have low or no activity. 

Another approach to the nature of the phosphate esterification reaction has been made with the use of isotope exchange methods. Boyer et al. and Swanson have shown that an exchange reaction between ATP and inorganic P is catalyzed by anaerobic mitochondria, and suggest that the exchange represents a reversible step in the process of oxidative phosphorylation. Similar conclusions were reached by Cohn and Drys-dale, who found in experiments with mitochondria that the oxygen of... 

In 1945 Lipmann found that a novel coenz3mae—coenzyme A— is required for the enzymic acetylation of sulfanilamide in pigeon liver preparations. Soon afterwards Nachmannsohn and Berman (see also ) found that a coenzyme is also required for the synthe of acetyl choline from choline and acetate in brain tissue, and this was found to be identical with the coenzyme of the acetylation of sulfanilamide, i Subsequently, three other reactions of acetate were found to involve coenzyme A the formation of acetoacetic acid from acetate, the s3mthesis of citrate from oxalacetate and acetate, - and the exchange reaction between acetyl phosphate and inorganic phosphate in bacterial extracts. " Thus, coenzyme A was shown to be a general coenzyme of acetylations, and... 

Interestingly, in the absence of sucrose and fructose, sucrose phosphory-lase will catalyze the exchange of inorganic phosphate, P , into glucose-l-phos-phate. This reaction can be followed by using as a radioactive tracer and observing the appearance of P into glucose-l-phosphate ... 

Inorganic reactions in the soil interstitial waters also influence dissolved P concentrations. These reactions include the dissolution or precipitation of P-containing minerals or the adsorption and desorption of P onto and from mineral surfaces. As discussed above, the inorganic reactivity of phosphate is strongly dependent on pH. In alkaline systems, apatite solubility should limit groundwater phosphate whereas in acidic soils, aluminum phosphates should dominate. Adsorption of phosphate onto mineral surfaces, such as iron or aluminum oxyhydroxides and clays, is favored by low solution pH and may influence soil interstitial water concentrations. Phosphorus will be exchanged between organic materials, soil inter-... 

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