Phosphates hydrolytic pathways

The phosphoryl group of the intermediate can enter two different reaction pathways leading to its decomposition. The phosphoryl group can either be transferred to water or to ADP. The hydrolytic pathway leading to the liberation of phosphate must be coupled to calcium translocation as it infers from the fixed coupling between calcium accumulation and phosphate liberation. 

The proportion of 1,4-anhydroribitol formed by treatment of teichoic acids and synthetic poly(ribitol phosphate) with alkali is small, and the major hydrolytic pathway involves the cyclic phosphate sequence. No 1,4-anhydroribitol glycosides have been observed in the alkaline hydrolyzates of teichoic acids possibly, the presence of a glycosyl substituent makes the reaction sterically less favorable than when such substituents are absent. 

Treatment of adenosine 5 -[ 3-morpholino]diphosphate with P 04]ortho-phosphate affords [y- 04]ATP, which has been used to study non-enzymatic hydrolytic pathways of ATP. Upon hydrolysis, the orthophosphate released was isolated, converted to trimethyl phosphate, and the isotope content analysed by mass spectrometry. In 1m and 0.1m HCl, the data suggest addition-elimination as the hydrolysis mechanism, with attack occurring predominantly at Py to... 

Phosphonate analogs to phosphate esters, in which the P—0 bond is formally replaced by a P—C bond, have attracted attention due to their stability toward the hydrolytic action of phosphatases, which renders them potential inhibitors or regulators of metabolic processes. Two alternative pathways, in fact, may achieve introduction of the phosphonate moiety by enzyme catalysis. The first employs the bioisosteric methylene phosphonate analog (39), which yields products related to sugar 1-phosphates such as (71)/(72) (Figure 10.28) [102,107]. This strategy is rather effective because of the inherent stability of (39) as a replacement for (25), but depends on the individual tolerance of the aldolase for structural modification close... 

Formation of dUMP in eukaryotes may occur by hydrolytic removal of phosphate from dUDP or from the conversions dCDP —> dCMP —> dUMP (steps k and V, Fig. 25-14). A more roundabout pathway is employed by E. coli dCDP —> dCTP —> dUTP —> dUMP (steps /c, /, and m, Fig. 25-14). One of the intermediates is dUTP. DNA polymerases are able to incorporate dUMP from this compound into polynucleotides to form uracil-containing DNA. Tire only reason that this does not happen extensively within cells is that dUTP is rapidly converted to dUMP by a pyrophosphatase (step m, Fig. 25-14). Tire uracil that is incorporated into DNA is later removed by a repair enzyme (Chapter 27). The presence of dUTP in DNA provides the basis for one of the most widely used methods of directed mutation of DNA (Chapter 26). 

Considerable effort has been applied to studies of ester hydrolysis catalyzed by imidazoles (76MI40700, 80AHC(27)241). Certainly, 1-acetylimidazole can be made enzymically, probably by the sequence acetyl phosphate + coenzyme A acetylcoenzyme A+phosphate, acetyl-coenzyme A + imidazole l-acetylimidazole+coenzyme A. In addition, the imidazolyl group of histidine appears to be implicated in the mode of action of such hydrolytic enzymes as trypsin and chymotrypsin, thereby engendering further interest in the process of imidazole catalysis. The two pathways which have been found to be involved are general base catalysis and nucleophilic catalysis. In the former (Scheme 26) a basic imidazole molecule can activate a water molecule to attack the ester at the carbonyl carbon, this being followed by the usual sequence of steps as in simple hydroxide ion hydrolysis. At high imidazole concentrations the imidazole molecules may be involved directly. 

The present information on the riboflavin biosynthetic pathway is summarized in Figure 1. Briefly, the pathway starts from GTP (1), which is converted into the first committed intermediate 2 by the hydrolytic release of pyrophosphate and of C-8 of the imidazole ring that are both catalyzed by a single enzyme, GTP cyclohydrolase II (reaction I). In Archaea and in fungi, that compound is transformed into 5-amino-6-ribitylamino-2,4(li/,3f/)-pyrimidinedione phosphate (5) by a reduction (reaction IV) that transforms the ribosyl side chain into the ribityl side chain (4) and by subsequent deamination (reaction V) of the pyrimidine ring yielding compound 5. In plants and in eubacteria (reactions II and III), these reaction steps occur in inverse order via the ribosylaminopyrimidine derivative 3. 

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