Phosphatase guanosine

Fig. 11. Modes of action of fluorine on osteoblastic cells, (a) Tyrosine phosphatase hypothesis in osteoblastic cells, fluoride ion directly inhibits tyrosine phosphatase. Inhibition of this enzyme enhances the tyrosine phosphorylation of signalling molecules induced by receptor tyrosine kinase, which leads to activation of the extracellular signal-regulated kinase (ERK) through the Ras pathway and enhanced cell proliferation, (b) G-protein hypothesis in osteoblast-like cells, fluoride ions form a complex with aluminum, probably fluoroaluminate, which interacts with guanosine 5 -diphosphate (GDP) to form guanosine 5 -triphosphate (GTP)-like molecule. Activation of the G, protein stimulates the tyrosine phosphorylation of signalling molecules by a yet unknown tyrosine kinase (Tyr Kin) and activation of the ERK kinase through the Ras pathway leads to enhanced cell proliferation. (Reproduced by permission of Elsevier from Ref. [175] ...

After purine nucleotides have been converted to the corresponding nucleosides by 5 -nucleotidases and by phosphatases, inosine and guanosine are readily cleaved to the nucleobase and ribose-1-phosphate by the widely distributed purine nucleoside phosphorylase. The corresponding deoxynucleosides yield deoxyribose- 1-phosphate and base with the phosphorylase from most sources. Adenosine and deoxyadenosine are not attacked by the phosphorylase of mammalian tissue, but much AMP is converted to IMP by an aminohydrolase (deaminase), which is very active in muscle and other tissues (fig. 23.20). An inherited deficiency of purine nucleoside phosphorylase is associated with a deficiency in the cellular type of immunity. 

J. Reizer, A. Reizer, M. H. Saier Jr., B. Bork and C. Sander (1993). Exopolyphosphate phosphatase and guanosine pentaphosphate phosphatase belong to the sugar kinase/actin/hsp 70 superfamily. Trends Biochem. Sci., 18, 247-248. 

Figure 9.133 HPLC separation of (/4) guanosine nucleotides and guanosine, injected amount 5 to 10 nmol each in 5 /xL, and (B) neopterin phosphates. The mixture of neopterin phosphates injected was produced by partial hydrolysis of 16 pmol of N IP with alkaline phosphatase and addition of 2, 3 -cNMP. (From Blau and Nieder-wieser, 1983.)...

On neutral or slightly alkaline hydrolysis, - or by treatment with bone phosphatase, guanylic acid is dephosphorylated to guanosine. Hence Levene perceived that guanylic acid is a phospho-guanosine, but many years elapsed before he was able to show the position of attachment of the phosphoryl group. 

Bolomey and Allen found that a non-specific phosphatase preparation (Bredereck ) containing a small amount of ribonuclease hydrolyzes ribosenucleic acid in such a manner that guanosine is liberated faster than adenosine, in the early stages of the hydrolysis the equivalent amount of free phosphoric acid is simultaneously formed. After hydrolysis of the purine nucleotide constituents has reached a maximum, hydrolysis of the pyrimidine nucleotides becomes appreciable. (If the ribosenucleic acid is subjected to the action of ribonuclease before treatment with the phosphatase, the reaction is much more rapid.) They therefore tentatively suggested that guanylic acid is the first mononucleotide liberated and adenylic acid the second. Hence, provided that... 

It would be of interest to halt the hydrolysis when liberation of guanosine and adenosine approaches a maximum, and determine whether the pyrimidine nucleotides are present as a dinucleotide or as the two mononucleotides. It is not clear whether the action of the non-specific phosphatase on an artificially-prepared, equimolecular mixture of the four mononucleotides has been studied (although the individual mononucleotides have been so examined by Bredereck, Beuchelt and Richter ), but Kobayashi has found that guanylic acid is hydrolyzed more readily than adenylic acid which, in turn, is hydrolyzed more readily than the pyrimidine nucleotides. Furthermore, Bredereck, et oZ. have shown that mild chemical hydrolysis of ribosenucleic acid with aqueous pyridine at 100° gives guanylic acid (G) plus a trinucleotide composed of adenylic (A), cytidylic (C), and uridylic (U) acids. On further hydrolysis in aqueous pyridine, adenylic acid is split off. Hence, in ribosenucleic acid, (G) is at one end of the molecule and, in the trinucleotide, (A) is at one end of the molecule. Possible formulas for the tetranucleotide are therefore... 

AGCU adenosine, guanosine, cytosine and uridine supplemented AP alkaline phosphatase APN aminopeptidase N AVP arginine vasopressin Be (homog) biochemical determination on culture homogenate CA carbonic anhydrase Calc calcitonin... 

AChE, BuChE, AChE molecular forms, lactate, p02, PCO2, carboxyles-terase (EC 3.1.1.1), alkaline phosphatase (EC 3.1.3.1), aspartate aminotransferase (AST, EC 2.6.1.1), alanine aminotransferase (ALT, EC 2.6.1.2), 7-glutamyltransferase (7-GT, EC 2.3.2.2), lactatedehydrogenase (LDH, EC 1.1.27), number of leukocytes (No leuco), corticosterone (CS), cyclic adenosine and guanosine monophosphate (cAMP, cGMP), OP metabolites (in case of parathion and fenitrothion), phosphonyl moiety attached to the enzyme in case of sarin (phosph. moiety), number of erythrocytes (No RBC), and tyrosine aminotransferase (TAT, EC 2.6.1.5), respectively. 

Adenyl cyclase systems isolated from mammals contain as a third component an additional guanosine triphosphate specific subunit and in all probability even more components whose function and structure are not known as yet. It is interesting to note that adenyl cyclases, Na-K-actlvated adenosine phosphatases (ATPases) have been located in the membrane of olfactory neurons and cAMP was found to have the highest concentration in man in the olfactory mucosa. 

Guanosine triphosphate cyclohydrolase I 2 pyrophosphorylase, phosphatase 3 diliydro-neopterin aldolase 4 hydroxymethyldihydropterin pyrophosphokinase 5 dihydropteroate synthase 6 dihydrofolate synthetase 7 dihydrofolate reductase 8 xanthine oxidase... 

The 5 -Substituted Nucleotides. These are adenosine-5 -phosphate, guanosine-5 -phosphate, uridine-5 -phosphate, and cytidine-5 -phosphate. All of them have been found among the hydrolysis products when ribonucleic acid is treated with snake venom diesterase or with intestinal phosphatase in the presence of arsenate. These compounds contain phosphate esterified at carbon 5 of the ribose moiety. 

Intestinal mucosa enzyme partially inhibited by arsenate leads to the formation of guanosine, cytidine, and cytidine-5 -phosphate. This preparation splits at (2) with subsequent partial dephosphorylation. Snake venom diesterase also sphts at (2). Prostatic phosphatase liberates... 

Nucleotidase occurs in certain leaves and plant seeds and has been purified from germinating barley. The enzyme hydrolyzes the 3 -phosphates of adenosine, inosine, guanosine, uridine, and cjrtidine as well as of coenzyme A. Purified enzyme preparations contain only traces of ATPase, acid phosphatase, and 5 -nucleotidase (126). 

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