Figure 1.

PI(3)P phosphatase activity is not a general property of protein tyrosine phosphatases. The activities of tyrosine-specific (GST-p61/62n), dual-specific (VHR), and inositol lipid phosphatases (GST-PTEN) were compared with that of myotubularin (GST-MTM1-His₆). (a) Phosphatase activity of each enzyme using pNPP as substrate. (b) Phosphatase activity toward PI(3)P as substrate. Phosphatase assays were carried out at 30°C as described in Materials and Methods. Enzyme specific activity is expressed as moles of phosphate released per minute per mole of enzyme (mean ± SEM).