Protein Tyrosine Phosphatases

The best-established direct targets of ROS signaling are protein tyrosine phosphatases (PTP).88,89,93 Tyrosine phosphorylation is controlled by the tightly regulated balance between tyrosine kinases and tyrosine phosphatases. All tyrosine phosphatases have a conserved 230-amino acid domain that contains a reactive and redox-regulated cysteine, which catalyzes the hydrolysis of protein phosphotyrosine residues by the formation of a cysteinyl-phosphate intermediate.94 This cyteine forms thiol phosphate, an intermediate in the dephosphorylation reaction of PTPs. Oxidation of this cyteine residue to sulfenic acid by H2O2 renders the tyrosine phosphatase inactive.94,95 Thus ROS significantly inhibit activity of tyrosine phos-phatases, resulting in increased tyrosine phosphorylation.

Inactivation of tyrosine phosphatases is involved in oxidative stress-induced activation of several receptor protein tyrosine kinases such as the EGFR and insulin receptor.96 This is particularly important with respect to Ang II, which mediates many of its signaling events in vascular cells through EGFR transactivation. H2O2 has also been shown to regulate MAP kinases through inhibition of tyrosine phosphatase activity.97

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