Phosphate

Abstract: A single solution reagent is described for the determination of phosphorus in sea water. It consists of an acidified solution of ammonium molybdate containing ascorbic acid and a small amount of antimony. This reagent reacts rapidly with phosphate ion yielding a blue-purple compound which contains antimony and phosphorus in a 1:1 atomic ratio. The complex is very stable and obeys Beer's law up to a phosphate concentration of at least 2 μg/ml.The sensitivity of the procedure is comparable with that of the stannous chloride method. The salt error is less than 1 %.

Abstract: Publisher Summary This chapter discusses the assay of inorganic phosphate, total phosphate, and phosphatases. The phosphomolybdate complex is reduced by ascorbic acid. The method is about seven times as sensitive as the Fiske–SubbaRow procedure and involves less pipetting. One can easily determine 0.01 micromole of phosphate. Pyrophosphate breaks down about 5% in the method and compounds such as glucose 1-phosphate also break down somewhat, so that the method is not very satisfactory for determining inorganic phosphate if labile phosphate esters are present in large excess. The sample of organic phosphate and a drop of magnesium nitrate solution in a small test tube are taken to dryness by shaking the tube in flame. The ashing procedure is rapid and is good for various biological materials and phosphate esters such as nucleic acid, carbohydrate phosphate esters, viruses, and phospholipids. The assay method of phosphatases for inorganic phosphate can be used as an assay for phosphatases hydrolyzing stable phosphate esters such as glucose-6-phosphate, ribose-5-phosphate, and histidinol phosphate. The enzyme incubation can be stopped with the one ascorbic-molybdate solution thus avoiding an extra pipetting.

Abstract: The use of phosphate solubilizing bacteria as inoculants simultaneously increases P uptake by the plant and crop yield. Strains from the genera Pseudomonas, Bacillus and Rhizobium are among the most powerful phosphate solubilizers. The principal mechanism for mineral phosphate solubilization is the production of organic acids, and acid phosphatases play a major role in the mineralization of organic phosphorous in soil. Several phosphatase-encoding genes have been cloned and characterized and a few genes involved in mineral phosphate solubilization have been isolated. Therefore, genetic manipulation of phosphate-solubilizing bacteria to improve their ability to improve plant growth may include cloning genes involved in both mineral and organic phosphate solubilization, followed by their expression in selected rhizobacterial strains. Chromosomal insertion of these genes under appropriate promoters is an interesting approach.

Abstract: A calorimetric assay for the determination of nanomole amounts of inorganic phosphate is described. The procedure combines a very high molar extinction with color stability and insensitivity to newly released phosphate from labile organophosphates. For studies on the energetics of active ion transport in various epithelial membrane systems, we needed a dependable ultramicromethod for the determination of inorganic phosphate. The most sensitive calorimetric method, that of Itaya and Ui (1) as modified by Hess and Derr (2), has some serious drawbacks: (a) the optical density of both the blank and the samples increase with time to an objectionable level, and more importantly (b) both ATP and ADP are hydrolyzed in the presence of the reagents. Both the highly acidic conditions and the catalytic effect of molybdate contribute to the hydrolysis of labile organophosphates and result in various phosphate levels being recorded according to the length of time allowed for color development (3,4). Since our laboratory started to measure ATPase activity routinely, we settled on our slight modification of the Baginski method of Pi determination (5). This method (through the use of a citratelarsenite mixture added immediately after the molybdate reagent) is relatively sensitive, color stable, and has the advantage of being insensitive to any newly released phosphate (e.g.,