P hydrolysis

Cyano derivatives of (18) are prepared by reaction of o-phenylenediamine with o-CcH4(CO)2N(CH2) COC(CN)z=NCGH4NMe2-p. Hydrolysis of the latter compounds give intermediates of the type o-Cr,H4(CO)2N(CH2) COCOCN which on condensation with o-phenylenediamine yield 3-phthalimidoalkylquinoxalin-2-ones, ... 

Li S, Dory P. Hydrolysis of cyclic orthoesters experimental observations and theoretical rationalization. Tetrahedron 1996 52 14841. 

AMP — A + P hydrolysis of ester bond - coupled to enei y-releasing processes... 

It appears to the author that the existence of a distinct glucose-6-phosphatase is well established for endoplasmic reticulum of liver, kidney, small intestine, and pancreas but additional studies appear to be required before a similar conclusion may be reached regarding the enzyme from other sources. It should be pointed out, however, that while glucose-6-P hydrolysis by enzymes from many sources may not result from specific glucose-6-phosphatase, this hydrolysis in these tissues may nonetheless be of metabolic significance. 

The first intensive investigation of the kinetics of step 2 was carried out by Herries et al. (496) in a study of C > p hydrolysis. The data gave linear double reciprocal plots and maximum velocities and Michaelis constants were measured as a function of pH. Similar studies on U > p have been carried out by others (497, 498), but these did not agree well with each other or with the later work of del Rosario and Hammes (499). In one case no indication was given of substrate purity and 1/15 M sulfate was employed (497). In the other product contamination was clearly a problem (498). 

The justification for (A) is manifold. NMR as interpreted by Jardetsky and his colleagues indicates that His 119 and 12 would be almost fully protonated at pH 4.5 in the protein and the complex. The pK of 3 -CMP is 5.7. Hummel and Witzel (456) showed that one proton is released when the complex is formed. Loeb and Saroff (475) detected chloride binding at low pH. Irie showed KC1 to be a competitive inhibitor of C > p hydrolysis, and Riiterjans and Witzel showed that the pfC values... 

The ks curve for C > p hydrolysis is not symmetrical, and a secondary acid pathway has been proposed to explain part of the activity at pH 4.0 (499). Perhaps the protonation of both histidines produces enough polarization of the phosphate to permit direct attack by water or stabilizes the transitional state in the formation of the pentacovalent intermediate. With excess protons present, protonation of the leaving group would be easy. If histidine is not involved as a base, the ks/Km curve should also be distorted according to this view. This description would not seem to fit their model. In any case it would be interesting to see if this acid pathway is different from the normal pathway with respect to in-line vs. adjacent mechanisms. An alternate proposal is that the protonation of the acetate-tris buffer was distorting the curve. Another factor to consider is the chloride behavior as a competitive inhibitor, but this would not affect fcs if it is strictly competitive. 

Bontchev PR, Papazova P. Hydrolysis of cephalosporins in strongly acidic medium. Pharmazie 1978 33(6) 346-348. 

Fig. 4. Metabolism of inositol lipids and inositol phosphates in stimulated cells. In the lipid cycle. Ptdlns is converted through Ptdlns 4-P to Ptd 4,5-P, which is hydrolysed upon receptor stimulation to yield diacylglycerol (DG) and Ins(1.4,5)P,. DG is phosphorylated via diacylglycerol kinase to give phospha-tidic acid (PA). PA is activated by CTP to form CDP-diacylglycerol which can combine with free inositol (Ins) to re-form Ptdlns. The other product of the Ptdlns 4,5-P, hydrolysis, Ins(l,4,5)P, may be de-phosphorylated to various InsP2 and InsP isomers which ultimately provide free inositol (Ins) for resynthesis of Ptdlns. Ins(l,4,5)Pj may be phosphorylated in steps to give an array of InsP4, InsP, or InsP6 isomers.

Summary of stimuli that induce both Ptdlns 4,5-P, hydrolysis and the release of arachidonate, and some examples of target tissues (from Refs. 6 and 8)... 

P Hydrolysis of the remaining phosphate group at C6 occurs, giving glucose. 

Ar( informative analog. Xylose has the same structure as that of glucose except tl at it has a hydrogen atom at C-.5 m place ol a hydroxymethyl group. The rate of A I P hydrolysis by hexoki-nasets markedly enhanced by the addition of xylose. Why ... 

De Jong, L.P.A., Van Dijk, C., and Benschop, H.P., Hydrolysis of the four stereoisomers of soman catalyzed by liver homogenate and plasma from rat, guinea pig and marmoset and by human plasma, Biochem. Pharmacol, 37, 2939, 1988. 

An effort is underway in our laboratory to determine transition state structures for phosphoryl transfer reactions by the use of secondary 0 isotope effects measured by the remote label method. The hypothesis is that an associative mechanism would have single bonds from phosphorus to the nonbridge oxygens in the transition state, whereas a dissociative mechanism would have enhanced bond order. So far we have determined the secondary 0 isotope effects on glucose-6-P hydrolysis at pH 4.5, 100°C (112), and by alkaline phosphatase (128). The chemical hydrolysis showed no isotope effect on P-O bond cleavage, which is consistent with a largely dissociative transition state without total conservation of bond order to phosphorus (i.e., a partial positive change exists on phosphorus). 

Zilliox, C., Debeire, P. Hydrolysis of wheat straw by a thermostable endoxylanase. Adsorbtion and kinetic studies, Enzym. Microbial Technol. 22, 58-63 (1998)... 

FIGURE 2.2 a/p Hydrolysis fold. (From Nardini, M., and B. W. Dijkstra, 1999, Current Opinion in Structural Biology 9 (6) 732-737. With permission.)... 

G-6-Pase is the enzyme catalyzing the hydrolysis of these substrates since activity is lost by brieiSy acidifying the preparation to pH 5. Under such conditions neither acid nor alkaline phosphatase activity is destroyed. Evaluation of Km for the various organic phosphates indicates that the ability of these substrates to inhibit competitively G-6-P hydrolysis is in accord with a single enzymatic activity (Crane, 1955). 

Moreau C, Durand R, Duhamet J, Rivaher P. Hydrolysis of finetose and glueose precursors in the presence of H-form zeolites 1. J Carbohydr Chem 1997 16 709-14. 

PP-ribose-P has been reported by others to be elevated by nucleosides and the trophic hormones, ACTH and TSH,which also presumably act by increasing ribose-5-P availability (Fox and Kelley, 1971). In addition. Estrogen has been observed to stimulate the synthesis of PP-ribose-P synthetase in rat uterus (Oliver, 1972). Finally, inhibition of PP-ribose-P hydrolysis provides a potential means of elevating intracellular PP-ribose-P levels (Fox and Marchant, in preparation). ... 

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