Phosphoryl fission

Neutral phosphate triesters will readily undergo acid or base-catalyzed hydrolysis with alkyl and/or phosphoryl fission. For example, trimethyl and triethyl phosphate will undergo hydrolysis in neutral water via an Sn2... 

The hydroxamic acid function in most alicyclic and aromatic compounds is stable to hot dilute acid or alkali, and derivatives cannot undergo normal base-catalyzed Lessen rearrangement. Di Maio and Tardella," however, have shown that some alicyclic hydroxamic acids when treated with polyphosphoric acid (PPA) at 176°-195° undergo loss of CO, CO.2, or H2O, in a series of reactions which must involve earlj fission of the N—0 bond, presumably in a phosphoryl-ated intermediate. Thus, l-hydroxy-2- piperidone(108) gave carbon monoxide, 1-pyrroline (119), and the lactams (120 and 121). The saturated lactam is believed to be derived from disproportionation of the unsaturated lactam. 

We have studied the extractant behavior of a series of compounds containing the carbamoylmethylphosphoryl (CMP) moiety in which the basicity of the phosphoryl group and the steric bulk of the substituent group are varied (10,LL). These studies have led to the development of extractants which have combinations of substituent groups that impart to the resultant molecule improved ability to extract Am(III) from nitric acid and to withstand hydrolytic degradation. At the same time good selectivity of actinides over most fission products and favorable solubility properties on actinide loading are maintained (11). 

Gould, K. L., and Nurse, P. (1989). Tyrosine phosphorylation of the fission yeast cdc2+ protein kinase regulates entry into mitosis. Nature 342 39-45. 

Krek, W., Marks, J., Schmitz, N Nigg, E. A., and Simanis, V. (1992). Vertebrate p34c 2 phosphorylation site mutants effects upon cell cycle progression in the fission yeast Schizosaccammyces pombe. J. Cell Sci. 102 43-53. 

Simanis, V., and Nurse, R (1986). The cell cycle control gene cdc2+ of fission yeast encodes a protein kinase potentially regulated by phosphorylation. Cell 45 261-268. 

The position was somewhat clarified by the isolation of 2- and 3-O-phos-phonucleosides from ribonucleic acid hydrolyzates in 92 to 100% yields,134 and also by the demonstration that 5-O-phosphonucleosides are also present in enzymic digests.49, 197 Yet this information gave no indication of the nature of the alkali-labile linkages. Thus, while the majority of the experimental evidence pointed to the phosphoryl residues as being doubly esterified with adjacent nucleosides, two facts remained apparently inexplicable on the basis of this type of structure. First, ready fission by alkalis, and secondly, the absence of 5-phosphates from alkaline hydrolyzates and their presence in enzymic digests. Both these facts have been explained by Brown and Todd in the following way.92... 

Further studies on 1,3-dipolar addition reactions of diazophosphonates have been recorded,122 and work on 2-diazo-l-hydroxyalkylphosphonates also continues.123 The ester (155 R = H) reacts with esters of acetylenedicarboxylic acid without liberation of nitrogen to give stereoisomeric C-phosphorylated pyrazolines, which can be decomposed with both phosphorus-carbon and carbon-carbon bond fission, affording mixtures containing dimethyl acetylphosphonate, dimethyl hydrogen phosphonate, and tri(alkoxycarbonyl)pyrazolines. In the reaction between the same diazophosphonate and diazomethane, the latter conceivably acts as a basic catalyst for proton transfer in a series of steps which includes phosphonate-phosphate isomerization. The importance of a labile proton is demonstrated by the fact that the ester (155 R = Me) does not react in the manner described above. 

Nakamura TM, Du LL, Redon C, Russell P (2004) Histone H2A phosphorylation controls Crb2 recruitment at DNA breaks, maintains checkpoint arrest, influences DNA repair in fission yeast. Mol Cell Biol 24(14) 6215-6230... 

Phosphorylation of ubiquitin ligases could have inhibitory effect as well. In the fission yeast Schizosaccharomyces pombe, PKA blocks APC activity. Moreover, the inhibitory effect of PKA seems to be dominant over the stimulatory effect of the polo-like kinase. Even if APC has been activated by polo-like kinase, addition of mammalian PKA to APC-containing fractions inhibits ubiquitination of the substrate cyclin... 

Phosphorylation at Thrl4 and TyrlS leads to inactivation of the CDKs. In the fission yeast, the weel kinase is responsible for this phosphorylation and in mammals, there are enzymes homologous to wee-1 kinase. It is not clear whether this kinase performs both phosphorylations. Phosphorylation at Thrl4 and TyrlS is of particular importance for regulation of CDK activity in mitosis. The CDC2-cychn B complex is maintained in an inactive state imtil the end of G2 phase by the phosphorylation of Thrl4 and TyrlS. At the G2/M transition, the inactive state is ended by the action of CDC2S phosphatase, which cleaves off the inhibitory phosphate residues. 

Metal Ion Effects. The metal ion effects on the acid-catalyzed hydrolysis of PPS also were examined by Benkovic and Hevey (5). However, they observed that in water near pH 3, the rate enhancement in the presence of an excess of metal ion was at most only threefold (Mg2+, Ca2+, Al3+) and in some cases (Zn2+, Co2+, Cu2+) the rate was actually retarded. We thought that the substrate PPS and Mg2+ ion should be hydrated heavily in water so that their complexa-tion for rate enhancement is weak. If, however, the hydrolysis is carried out in a solvent of low water content, such complexation would not occur, and therefore, the rate enhancement might be more pronounced. This possibility appears to be supported by the fact that the active sites of many enzymes are hydrophobic. Of course, there is a possibility that the S—O fission may not require metal ion activation. In this connection, it is interesting to note that in biological phosphoryl-transfer reactions the enzymes generally require divalent metal ions for activity (7, 8, 9), but such metal ion dependency appears to be less important for sulfate-transfer enzymes. For example, many phosphatases require metal ions, but no sulfatase is known to be metal... 

In the above aminolysis reactions, Mg2+ ion always activates P—O fission. Other divalent metal ions behave similarly. Change of nucleophile might result in the change of P—O to S—O fission. To pursue the possibility of metal ion catalyzed S—O fission under neutral conditions, we examined the catalysis of the Zn2+-pyridine-2-carboxaldoxime (Zn2+PCA) complex, since catalytic activity of this complex has been well known in some acyl and phosphoryl transfer reactions (18, 19, 20). However, the results described below again indicate that the complex promotes an exclusive P-O bond fission (21). 

Reactions of 2-Pyridylmethylphosphosulfate (23). As illustrated in Figure 16, two modes of S—O fission are conceivable for the reaction of 2-pyridylmethylphosphosulfate (PMPS) (a) A divalent metal ion may bridge pyridyl and phosphoryl groups, leaving the sulfate group free. Such chelation would lower the pKa of the leaving phosphoryl group and assist S—O fission by either unimolecular or... 

The effects of these metal ions on the rates of hydrolysis are shown in Figure 20a. It is clear that Zn2+ and Cu2+ ions inhibit the hydrolysis, while Mg2+ ion slightly accelerate the rate. Thus, the results are the opposite of our original expectation that chelation of phosphoryl oxygen with metal ion (Figure 16a) would activate S-O bond fission. 

Also ]. C. Ford, F. al Khodairy, E. Fotou, K. S. Sheldrick, D. J. Griffiths, and A. M. Carr. 14-3-3 protein homologs required for the DNA damage checkpoint in fission yeast. Science, 265 (5171), 533-535, 1994. Also N. Rhind, B. Furnari, and P. Russell. Cdc2 tyrosine phosphorylation is required for the DNA damage checkpoint in fission yeast. Genes Devel, 11 (4), 504-511, 1997. 

Thus, as with ribonuclease hydrolysis, chemical hydrolysis of the polymer causes fission of a link involving a secondary acidic group of a phosphoryl radical it is not yet known (a) whether the products are identical, and (b) whether the same phospho groups are split in each type of depolymerization. Accepting Gulland s titration results, possible formulas for the tetranucleotide (in which polymerization takes place at A or B) are as follows. 

Other phosphoryl transfer mechanisms are an associative, two-step mechanism (An + Dn) and a concerted mechanism (ANDN) with no intermediate. The AN+DN mechanism is an addition-elimination pathway in which a stable pentacoordinate intermediate, called a phosphorane, is formed. This mechanism occurs in some reactions of phosphate triesters and diesters, and has been speculated to occur in enzymatic reactions of monoesters. In the concerted ANDN mechanism, bond formation to the nucleophile and bond fission to the leaving group both occur in the transition state. This transition state could be loose or tight, depending upon the synchronicity between nucleophilic attack and leaving group departure. The concerted mechanism of Fig. 2 is drawn to indicate a loose transition state, typical of phosphate monoester reactions. 

Fig. 4 A transition state for phosphoryl transfer in which bond fission is ahead of bond formation to the phosphoryl acceptor (nucleophile) is loose, and resides in the lower right region. In the reverse situation a tight transition state results in the upper left region. If the sum of bond order to nucleophile plus leaving group is unity, the transition state will lie on the synchronicity diagonal.

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