Acetyl phosphate, hydrolysis rate

Attention has been drawn to the potential of phosphoric acid anhydrides of nucleoside 5 -carboxylic acids (14) as specific reagents for investigating the binding sites of enzymes. For example, (14 B = adenosine) inactivates adenylosuccinate lyase from E. coli almost completely, but has little effect on rabbit muscle AMP deaminase. The rate of hydrolysis of (14) is considerably faster than that of acetyl phosphate, suggesting intramolecular assistance by the 3 -hydroxyl group or the 3-nitrogen atom. 

A proper inference. What information do the A G° data given in Table 14,1 provide about the relative rates of hydrolysis of pyrophosphate and acetyl phosphate ... 

Triose, tetrose, and pentose phosphates enriched with C have been prepared by the Kiliani-Fischer reaction on the terminal phosphates of the next lower aldose. The mixed nitriles were separated on Dowex 1-X8 resin and reduced with hydrogen over Pd-BaS04. The synthesis of D-glucose 2-phosphate by phosphorylation of l,3,4,6-tetra-0-acetyl-j3-D-glucopyranosyl chloride, itself prepared by 2 1 acetyl migration, has been reported. Rates of phosphate hydrolysis in 0.25 M sulphuric acid and in 0.25 M sodium hydroxide were measured for D-glucose monophosphates in the former the order was 1-phosphate > 2-phosphate > 3-phosphate > 6-phosphate while in the latter it was 3-phosphate > 6-phosphate > 2-phosphate > 1-phosphate. ... 

Using a cell membrane preparation made from guinea pig liver cortex, Bader and Sen (1966) demonstrated that acetyl phosphate and car-bamyl phosphate were hydrolyzed at a rate dependent on K which was comparable to the Na" -I- K -dependent hydrolysis of ATP. These two hydrolytic activities were closely related with regard to monovalent cation specificity, Michaelis constants, optimal pH, and inhibition by ouabain. Accordingly, fiiey have suggested that an acyl phosphate may be a functional intermediate in the system. Other acyl phosphatases have no cation requirements and are not inhibited by Hg+. ... 

Several 1 -phosphates of deoxyfluoro sugars were prepared, and their acid-catalyzed hydrolysis was studied. 2-Deoxy-2-fluoro- (580), 3-deoxy-3-fluoro- (582), 4-deoxy-4-fluoro- (583), and 6-deoxy-6-fluoro-a-D-gluco-pyranosyl phosphates (584) were prepared by treatment of the corresponding per-( -acetylated )9-D-glucopyranoses with phosphoric acid [the p anomer (581) of 580 was prepared by a different method]. The first and second ionization constants (pA a, and pA a2) of these compounds were determined potentiometrically, as well as by the F-n.m.r. chemical shifts at a series of pH values, and then the rate constants of hydrolysis for neutral (B) and monoanion (C) were decided. The first-order rate-constants (k) for 580-584 and a-D-glucopyranosyl phosphate (in Af HCIO4,25 °) were 0.068, 0.175, 0.480, 0.270, 1.12, and 4.10 (all as x lOVs), respectively. The rate... 

The activity of carbamoyl phosphate synthase I is determined by A -acetylglutamate, whose steady-state level is dictated by its rate of synthesis from acetyl-CoA and glutamate and its rate of hydrolysis to acetate and glutamate. These reactions are catalyzed by A -acetylglu-tamate synthase and A -acetylglutamate hydrolase, respectively. Major changes in diet can increase the concentrations of individual urea cycle enzymes 10-fold to 20-fold. Starvation, for example, elevates enzyme levels, presumably to cope with the increased production... 

The characteristic features of hydrolysis of diaryl phosphate monoanions (pronounced influence of leaving group on the rate of hydrolysis, k o/k = 1.6, and AS = —25 euu7y) also fail to support a metaphosphate mechanism118>. Hydrolysis of the acetyl phenyl phosphate monoanion is likewise far slower than that... 

Comparison of Second-Order Rate Constants (M 1sec 1) in Hydrolysis (or Acetyl and Phosphoryl Transfer) of 4-Nitrophenyl Acetate, Methyl Acetate and Bis(4-nitrophenyl) Phosphate... 

To understand the role of metal ions in hydrolysis reactions, it is useful to first consider the background hydrolysis reactions. Table 6.1 lists the second-order rate constants for hydroxide-catalyzed hydrolysis of various substrates. The reactivity of methyl acetate (first entry in Table 6.1) [16] is comparable to those of other unactivated esters found in nature (e.g. acetyl choline and carboxyl esters in phospholipids). The reactivity of N-methylacetamide (second entry in Table 6.1) [17] is comparable to those of typical peptides (1.1 x 10 6 m-1 s 1) [18] and that of dimethyl phosphate (P-O bond... 

Enzymatic catalysis lowers AG to accelerate the reaction rate, but does not affect the AG° that controls the position of equilibrium. However, cells also have an elegant ability to overcome an unfavorable equilibrium by coupling an endothermic reaction with exothermic ATP hydrolysis. For example, the reaction of acetate with coenzyme A (CoASH) giving acetyl CoA is uphill by about 7 kcal/mol. The hydrolysis of ATP to ADP and phosphate is downhill by about the same amount. By coupling these two reactions shown below for acyl-CoA synthetase, the cell achieves a total AG° of almost 0 for a ATgq of about 1. The phosphorylation of acetate by ATP improves the leaving group for the second reaction with CoASH. There are many enzymes whose catalytic process remains a mystery enzymes still have much to teach us about reaction mechanisms. 

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