Inhibition of phosphatase

Boavida, M.-J., and R. G. Wetzel. 1998. Inhibition of phosphatase activity by dissolved humic substances and hydrolytic reactivation by natural UV. Freshwater Biology 40 285—293. 

The lysosomal and the soluble fractions of acid phosphatase were compared in several other ways. The values (milf) for the lysosomal fractions on various substrates were -glycerophosphate, 1.6 fructose 1,6-diphosphate, 2.0 p-nitrophenyl phosphate, 1.6 AMP, 0.43 they were not significantly different from those obtained with the soluble fraction. The pH-activity curves with these substrates were similar for the two fractions. Inhibition of phosphatase activity of the lysosomal and soluble fractions occurred at approximately the same concentration of fluoride or n- (+) -tartrate when j8-glycerophosphate, AMP, or fructose 1,6-diphosphate were used as substrates. However, with p-nitrophenyl phosphate... 

B31. Bodansky, 0., Influence of magnesium and cobalt on inhibition of phosphatases of bone, intestine and osteogenic sarcoma by amino acids. J. Biol. Chem. 179, 81-102 (1949). 

Since disturbed acid phosphatase activity has been associated with pathological conditions, the research has focused on the development of diagnostic methods for detection of activity as a marker for the onset of the disease, and in some extent to the development of inhibitors rather than activators to treat those conditions in which the increase in enzyme activity has a direct effect on the evolution of the disease. In particular, only the development of bisphospho-nate derivatives as inhibitors for tartrate-resistant acid phosphatase found their way to the market for treatment of osteoporosis [41], Typical inhibition of phosphatase activity includes anionic species such as L-(+)-tartrate, phosphate, vanadate, molybdate, and fluoride and neutral molecules such as formaldehyde. Vanadate ion,, is a competitive unspecific inhibitor for acid phosphatases by forming transition state analogs. Other oxoanions such as molybdate and tungstate also show inhibitory effects on... 

Several phosphatase inhibitors are available and have been useful in many aspects of smooth muscle research. Okadaic acid was the first inhibitor to be widely used and inhibition of phosphatase activity by this compound was demonstrated using smooth muscle (Hartshorne et al., 1989). Calyculin A was also used in several earlier studies. Since 1990 other compounds have been described as phosphatase inhibitors. These are remarkable in that despite considerable differences in structure, they are relatively specific as phosphatase inhibitors. These inhibitors include tau-tomycin, as antifungal antibiotic produced by Strep-tomyces (MacKintosh and Klumpp, 1990 Hori et al.,... 

P-myosin is higher than that of the isolated catalytic subunit. Thus dissociation of the trimeric phosphatase could be a regulatory mechanism. The factors involved in dissociation of PPlc are not established, although there is the suggestion that arachidonic acid is implicated. It is possible that dissociation of the trimeric phosphatase is the end result of the G-protein-linked inhibition of phosphatase activity, observed in several systems. Another possibility is that the trimeric phosphatase binds only to phosphorylated myosin and has a lower affinity for the dephosphory-lated form. Whatever the scenario imagined, it is clear that much remains to be learned about regulation of myosin phosphatase activity. 

Like cyclosporine, tacrolimus inhibits T-cell activation by inhibiting calcineurin. Tacrolimus binds to an intracellular protein, FK506-biruiing protein-12 (FKBP-12), an immunophilin structurally related to cyclophilin. A complex of tacrolimus-FKBP-12, Ca, calmodulin, arui calcineurin then forms, arui calcineurin phosphatase activity is inhibited. described for cyclosporine and depicted in Figure 52—1, the inhibition of phosphatase activity prevents dephosphorylation and nuclear translocation of NFAT arui inhibits T-cell activation. Thus, although the intracellular receptors differ, cyclosporine and tacrolimus target the same pathway for immunosuppression. 

Ichikawa K, Ito M, Hartshorne DJ (1996a) Phosphorylation of the large subunit of myosin phosphatase and inhibition of phosphatase activity. J Biol Chem 271 4733-4740... 

Mortland and Gieseking (1952) found that all the clays that they studied exerted an inhibiting effect upon the enzymatic hydrolysis of organic phosphorus c ompounds. The effect of the clays was as follows montmorillonite > Cisne > illite > kaolinite. The inhibition of phosphatase activity corresponded closely to the base exchange capacity of the clays, and was due primarily to their effect on the enzyme and riot to adsorption of the organic phosphorus compounds by the clays. 

Recent observations suggest that at least okadaic acid may have some unknown activities outside the inhibition of phosphatase. This is based on the observation that methyl okadate does show a similar toxic effect in cell cultures than okadaic acid, but methyl okadate is 500 times less potent than okadaic acid to inhibit phosphatases (unpublished results) (Figure 6.2). 

FIGURE 6.2 Inhibition of phosphatase caused by okadaic acid and methyl okadate. 

Li, D.W.-C. et al., Okadaic acid-induced lens epithelbial cell apoptosis requires inhibition of phosphatase-1 and is associated with induction of gene expression including p53 and bax, Eur. J. Biochem., 257, 351, 1998. 

Arendt, T. et al.. Paired helical filament-like phosphorylation of tan, deposition of p/A4-amyloid and memory impairment in rat induced by chronic inhibition of phosphatase 1 and 2A, Neuroscience, 69, 691, 1995. 

Miller, C., Zhang, M., He, Y, Zhao, J., Pelletier, J.P., Martel-Pelletier, J., and Di Battista, J.A. (1998) Transcriptional Induction of Cyclooxygenase-2 Gene by Okadaic Acid Inhibition of Phosphatase Activity in Human Chondrocytes Co-Stimulation of AP-1 and CRE Nuclear Binding Proteins, J. Cell. Biochem. 69, 392 13. 

An interesting approach to overcome the difficulties in supplying ascorbate to cultured cells and to correctly interpret its biological effects was offered by Hata and Senoo (1989). Instead of ascorbate, ascorbic acid 2-phosphate was used to supplement culture media. By esterifying one of the enediol groups, the autoxidability of ascorbate is essentially abolished (see Fig. 1). Upon uptake, the phosphate residue is eliminated by phosphatases, and free ascorbate becomes available intracellularly. Of course, the usefulness of this procedure depends on the absence of phosphatases in the medium, which has to be ensured by frequent exchange of medium or inhibition of phosphatases. 

Macrocyclic paracyclophanes were evaluated on inhibition of phosphatase Cdc25B. Compound 42 and 43 were found to be the most potent (IC50 values of 3.4 and 3.5 fiM, respectively) with greater than threefold selectivity over other phosphatases like PTPIB, PTPa, and PP2A (Figure 16.3). 

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