Abstract
In the past few years, a diverse family of receptor-like and nontransmembrane protein tyrosine phosphatases (PTPases) have been identified and characterized at the level of primary structure. Progress is now being made towards defining physiological processes in which the activity of PTPases is important. One thing seems clear: the PTPases cannot be regarded simply as antagonists of the protein tyrosine kinases (PTKs)--rather, they have the potential to act both positively and negatively in mediating cellular signalling responses.
