Inorganic phosphate esters

Total phosphorus includes colloidal inorganic phosphate, casein (organic) phosphate, soluble inorganic phosphate, ester phosphate and phospholipids. 

The concepts of destabilization of reactants and stabilization of products described for pyrophosphate also apply for ATP and other phosphoric anhydrides (Figure 3.11). ATP and ADP are destabilized relative to the hydrolysis products by electrostatic repulsion, competing resonance, and entropy. AMP, on the other hand, is a phosphate ester (not an anhydride) possessing only a single phosphoryl group and is not markedly different from the product inorganic phosphate in terms of electrostatic repulsion and resonance stabilization. Thus, the AG° for hydrolysis of AMP is much smaller than the corresponding values for ATP and ADP. 

Three types of synthases catalyze the addition of phosphoenolpyruvate (PEP) to aldoses or the corresponding terminal phosphate esters. By concurrent release of inorganic phosphate from the preformed enolate nucleophile, the additions are essentially irreversible. None of the enzymes are yet commercially available and little data are available oil the individual specificities for the aldehydic substrates. A bacterial NeuAc synthase (EC 4.1.3.19) has been used for the microscale synthesis of A -acetylncuraminic acid from Af-acetyl-D-mannosamine31 and its 9-azido analog from 2-acetamido-6-azido-2,6-dideoxy-D-mannose32. 

The highly electrophilic character of the POf ion would suggest a very unselective phosphorylation behavior. For example, the ratio of alkyl phosphate to inorganic phosphate obtained in hydrolyses of phosphoric esters in water/alcohol mixtures should reflect the molar ratio of water and alcohol. This is indeed found in numerous cases, e.g. in the hydrolysis of phenyl and 4-nitrophenyl phosphate monoanions 97) or of 4-nitrophenyl phosphate dianions 65) at 100 °C in methanol/ water mixtures of various compositions, as also in the solvolysis of the acetyl phosphate dianion at 37 °C 97) or of phosphoenol pyruvate monoanions 82). Calculations of the free energy of the addition reactions of water and ethanol to the POf ion support the energetic similarity of the two reactions 98) (Table 4). 

The thioester hypothesis can be summed up as follows the formation of thiols was possible, for example, in volcanic environments (either above ground or submarine). Carboxylic acids and their derivatives were either formed in abiotic syntheses or arrived on Earth from outer space. The carboxylic acids reacted under favourable conditions with thiols (i.e., Fe redox processes due to the sun s influence, at optimal temperatures and pH values) to give energy-rich thioesters, from which polymers were formed these in turn (in part) formed membranes. Some of the thioesters then reacted with inorganic phosphate (Pi) to give diphosphate (PPi). Transphosphorylations led to various phosphate esters. AMP and other nucleoside monophosphates reacted with diphosphate to give the nucleoside triphosphates, and thus the RNA world (de Duve, 1998). In contrast to Gilbert s RNA world, the de Duve model represents an RNA world which was either supported by the thioester world, or even only made possible by it. 

High resistance to almost all inorganic chemicals, ammonia being the most important exception. Resistance to most organic compounds, except low molecular weight polar organics. Least resistant of the fluorocarbon rubbers to methanol and phosphate ester based hydraulic fluids. 

Sucrose phosphorylase can then be regarded as a rather versatile transglucosidase, capable of exchanging glycosidic and ester bonds and of donating D-glucose to a variety of substrates such as ketoses, an aldose, inorganic phosphate and arsenate. 

Many methods have been developed in which a product of the reaction is chemically modified to produce a substance with a particular spectral property. The inorganic phosphate released by the hydrolysis of phosphate esters may be measured by simple chemical methods (Fiske and Subbarow) after the enzyme reaction has been stopped. Such techniques are often convenient but do not lend themselves to the measurement of initial velocity. 

It had been known from at least the time of Pasteur that the presence of sodium or potassium phosphate aided the progress of a yeast fermentation. Later intensive study showed that a complex group of enzymes (phosphatases and phosphorylases) was responsible for the phosphorylation, dephosphorylation and interconversion of D-glucose 6-phosphate, D-fructose 6-phosphate, D-fructose 1,6-diphosphate and similar substances in various types of cells and muscle tissue. Detailed reviews of the field are available. - A further advance was made in 1936, when Cori and Cori noted that in certain circumstances well-washed frog muscle immersed in a sodium phosphate buffer utilized the inorganic phosphate to produce a new hexose phosphate (the Cori ester). This compound was later shown to be a-D-glucopyranose-l-phosphate and yielded crystalline dipotassium and brucine salts. The Cori ester arose because... 

Cori ester + D-fructose sucrose + inorganic phosphate,... 

Previous methods for the preparation of salts of geranyl diphosphate and other allylic isoprenoid diphosphates are based on condensation between the alcohol and inorganic phosphate by trichloroacetonitrile as originally reported by Cramer and modified by Popjak The reaction generates a complex mixture of organic and inorganic polyphosphates which must be separated by chromatography. The desired diphosphate ester has been prepared on small... 

Okazaki etal. showed that for the same fluoride level supplied, the precipitation of fluorapatite using an organic phosphate source (phosphate ester monomer) instead of an inorganic phosphate source led to higher fluoride contents [127],... 

Alcohols react with inorganic acids to form esters, e.g. tosylate esters (see Section 5.5.3) and phosphate esters. Phosphate esters are important in nature since they link the nucleotide bases together in DNA (see Section 4.8). 

Milk acid phosphatase has been purified to homogeneity by various forms of chromaotgraphy, including affinity chromatography purification up to 40 000-fold has been claimed. The enzyme shows broad specificity on phosphate esters, including the phosphoseryl residues of casein. It has a molecular mass of about 42 kDa and an isoelectric point of 7.9. Many forms of inorganic phosphate are competitive inhibitors, while fluoride is a powerful non-competitive inhibitor. The enzyme is a glycoprotein and its amino acid composition is known. Milk acid phosphatase shows some similarity to the phosphoprotein phosphatase of spleen but differs from it in a number of characteristics. 

Calcification can be visualized in two phases. In the first phase, phosphate accumulates within the matrix vesicles through the enzyme hydrolysis of inorganic pyrophosphate (and perhaps other phosphate esters)458. ... 

Inorganic acid esters nitrates (e.g. methyl nitrate, nitroglycol, nitroglycerine), silicates (e.g. ethyl silicate), phosphates (e.g. triphenyl phosphate, tricresyl phosphate), mixed esters of nitric and hydrochloric acid (e.g. chlorohydrin dinitrate). 

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