Phosphatase inactivating system

A phosphatase-inactivating system is found in the soluble fraction of liver (Beaufay et al., 1954). Such inactivation may be inhibited by epinephrine in excess of the substrate and by chelating agents such as Versene. The products of reaction tend to inhibit slightly. In this respect phosphate has a more pronounced effect than does glucose. 

Recently, Denu and Tanner have demonstrated specific and reversible inactivation of a protein tyrosine phosphatase by oxidation of the active site cysteine residue to a sulfenic acid by hydrogen peroxide [84], The switching of metal ions between different redox states in calcinewin and purple acid phosphatase may represent yet another system by which signal transduction can be regulated by redox state changes in vivo. 

The unusually high stringency and low pH of the hybridization conditions are based on empirical observations from the Drosophila system. The high temperature (and possibly also the acid conditions) is probably important for the inactivation of endogenous alkaline phosphatase activity. 

Fig.2 shews the kinetics of phosphorylation of LEC-II,the 62kDa kinase and the 64kDa polypeptide by thylakoids upon activation by illumination, and deactivation upon addition of DCMJ and methylviologen, a condition v ere PCJi2 and cyt.b563 are rapidly oxidized. It can be seen that the inactivation of the kinase is immediate, as it is upon addition of ferricyanide v en the activation is performed with the ferredoxin-NADPH system as described under "Methods" (not shewn). The dephosphorylation of the proteins was inhibited by NaF 10 iriM in the absence of this inhibitor both proteins are dephosphorylated by the thylakoid bound phosphatase with no lag, with half times of ca. 20 and 40 min,respectively, for LHC-II and the kinase (fig.3). 

Brush-border membrane alkaline phosphatase (EC 3.1.3.1) of the rat small intestine was inactivated in an in vitro Fe /ascorbate oxygen-radical generating system (Dudeja and Brasitus 1993). The activities of sucrase, maltase, leucine amino-peptidase, and y-glutamyl transpeptidase were unchanged. 

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