Inosine-5 -phosphate, hydrolysis

On neutral hydrolysis of the barium salt it gives barium phosphate and inosine. On hydrolysis with 0.1 AT hydrochloric acid (during 1 hour at 100 ), it gives rise - to hypoxanthine and a phospho-D-ribose. The structure of this phosphoribose was readily shown by oxidation with... 

Arsenate similarly replaces phosphate in various phosphorolysis reactions, so that sucrose phosphorylase catalyzes the hydrolysis of sucrose in its presence (23), potato phosphorylase can hydrolyze amylose and amylopectin (24), nucleoside phosphorylase can hydrolyze inosine... 

The 3- and 5-phosphates of D-ribose have both been obtained through the hydrolysis of naturally occurring ribosides. In 1908 Levene and Jacobs122 subjected the barium salt of inosinic acid to acid hydrolysis and obtained a pentose phosphate as its barium salt. Shortly thereafter the same authors78 showed that, under the conditions which normally convert a pentose to a pentaric acid, this phosphate was oxidized only to a phosphorylated D-ribonic acid and it was evident, therefore, that... 

Phosphorylation of XLVII with phosphorus oxychloride in pyridine solution, followed by hydrolysis to remove the methyl and isopropylidene residues, gave D-ribose 5-phosphate (XLVIII) which, as its barium salt, was found to be identical with the barium salt of the D-ribose phosphate from inosinic acid. By way of further confirmation of the structure of D-ribose 5-phosphate, Levene, Harris and Stiller129 showed that in methanolic hydrogen chloride solution both the natural and synthetic material mutarotated in a manner characteristic of a sugar which can form only a furanoside. 

The substrates most generally used in measuring the activity of NTP are AMP or IMP (inosine-5"-phosphate). However, these substrates are organic phosphate esters and thus can be hydrolyzed to an appreciable degree by other nonspecific (alkaline) phosphatases, even at a pH as low as 7.5, which is the pH assumed optimal for NTP activity. Methods for the estimation of NTP in serum must therefore incorporate some means for correcting for the hydrolysis of the substrate by the nonspecific phosphatases. 

Inosinic acid (1), the first nucleotide to be discovered, was isolated over a century ago from beef extract by Liebig. Mild, acid hydrolysis of this nucleotide yielded a ribose phosphate (2) which, by oxidation with nitric acid, gave a ribonic acid phosphate (3), but not a ribaric acid phosphate. These studies by Levene and his associates showed that the phosphoric (phospho) group is bound to the 5-hydroxyl group of the ribosyl moiety in 1 hence, inosinic acid is inosine 5 -phosphate. Adenylic acid (4), isolated from muscle, was converted enzymically (by adenylic... 

Oxidation of (8) yielded a ribonic acid phosphate (9), whose properties differed from those of the ribonic acid 5-phosphate obtained by similar hydrolysis and oxidation of inosine 5 -phosphate. Moreover, reduction of (8) allegedly gave a ribitol phosphate (10) which was optically inactive. From these studies, it followed that the phosphoric moiety in (10) is esterified by the 3-hydroxyl group of the ribitol moiety. Similarly, a yeast adenylic acid, obtained from an alkaline hydrolysate of yeast ribonucleic acid, was deaminated to an inosinic acid that was different... 

Purine nucleoside phosphorylase (PNP). In contrast to lU-NH, PNP appears to use extensive contacts with the purine ring to promote catalysis and relatively few contacts with the ribosyl ring. The crystal structure of PNP has been determined in a complex with an iminosugar inhibitor, immucillin H, which was developed based on TS analyses of PNP-catalyzed hydrolysis and arsenolysis reactions. TS analysis revealed that the enzyme catalyzes a dissociative A Dn mechanism. The crystal structure was compared with the structures determined by Ealick and coworkers ° of PNP in a Michaelis complex analogue, PNP-inosine-sulfate, and a product complex, PNP-a-D-ribose-l-phosphate-hypoxanthine. 

Fig. 16 A schematic mechanism of PNP-catalyzed inosine phosphorolysis showing electrophile migration. This mechanism is based on cocrystal structures of PNP and TS analyses of inosine hydrolysis and arsenolysis. A large number of direct and water-mediated enzyme-substrate contacts hold the leaving group hypoxanthine and the nucleophile phosphate almost immobile while the ribosyl ring (the electrophile), because of the small number of contacts with the enzyme, is able to migrate from leaving group to nucleophile.

TS analysis was performed for two PNP-catalyzed reactions, arsenolysis of inosine using arsenate as a phosphate analogue, and a pre-steady state TS analysis of PNP-catalyzed inosine hydrolysis. The ribosyl ring KIEs (Table 7) were typical of those observed previously for other reactions of A -ribosides, indicating an AnDn mechanism for hydrolysis and either an AnDn or Dn An for arsenolysis. The... 

Mild acid hydrolysis of the deaminated purine nucleotides, xanthylic acid and inosinic acid, gives the purine bases (xanthine and hypo-xanthine, respectively) and a reducing sugar phosphate. The same hydrolytic products are obtained by use of a specific pancreatic enzyme. On the other hand, mild alkaline hydrolysis of a nucleotide, or treatment with the appropriate enzyme, liberates free phosphoric acid and a non-reducing compound of base and sugar, known as a nucleoside. (Hydrolysis of ribosenucleic acid with fairly dilute ammonia under pressure, during 3.5 hours at a bath temperature of 175 to 180 , gives an equimolecular mixture of four nucleosides). 

Isopropylideneinosine added to a cold mixture of PCI3 and trimethyl phosphate as catalyst, stirred 1 hr. at 0, the crude intermediate dissolved in ice water, treated with 6 N NaOH, and warmed at 70° inosine 5 -phosphite. Y 90% by paper chromatography. F. e., also phosphorylation by oxidation with chlorine after partial hydrolysis, s. M. Yoshikawa, M. Sakuraba, and K. Kusashio, Bull. Chem. Soc. Japan 43, 456 (1970). 

Ribose phosphates can be obtained from nucleotides. Mild acid hydrolysis of inosinic acid (12.19a), for example, yields ribose-5 -phosphate and inosine whereas neutral hydrolysis yields inositol and phosphate. 

Purine nucleotides are modified by a variety of enzymes, including those that attack the phosphate group and those that split the glycosidic bond. In addition to these, there are changes in the bases in which the amino groups of adenylic acid and guanylic acid are removed by specific deaminases. With these cases excepted (i.e., the formation of inosinic and xanthylic acids), degradation of purines occurs after hydrolysis to yield the free base. 

Lipid oxidation products and their reaction products with amino acids (proteins) have a considerable influence on the typical odour and taste of meat. Particularly significant aminocarboxylic acids include glutamic acid, alanine, threonine and lysine, guanidine compounds (creatine and creatinine), quaternary ammonium compounds (choline and carnitine), peptides (P-alanylhistidine peptides and some products of proteolysis), free nucleotides, nucleosides and their bases (especially inosine 5 -monophosphate, IMP), proteins, carboxylic acids (especially lactic acid), sugars (mainly glucose, fructose and their phosphates, ribose formed by hydrolysis of free nucleotides) and some vitamins (especially thiamine). Some of these compounds, such as glutamic acid and IMP, are additionally used as food additives, namely as flavour enhancers. 

D-Ribose 5-phosphate is a normal metabolite in plants and animals. It was first prepared by acid hydrolysis of inosinic acid or from adenosine 5 -phosphate . It is formed enzymically from ribose and ATP . Synthesis has been carried out by phosphorylating 2,3-isopropylidene-methyl-D-ribofuranoside °. ... 

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