Partial purification and characterization of protein tyrosine kinases from normal tissues

Abstract

Three membranous protein tyrosine kinases (PTKs) have been partially purified from human placenta and pig brain. The two placental enzymes (PTK-1 and -2) are distinct with respect to solubility in detergents, molecular weight, and enzymatic properties. The brain protein tyrosine kinase resembles placental PTK-1 with respect to molecular weight and some kinetic properties. However, stimulation of brain PTK is greater with Mn2+ than with Mg2+ whereas placental PTK-1 gives higher rates with Mg2+ than with Mn2+. All three enzymes are inhibited about 50% by 0.1 M NaCl. A monoclonal antibody raised in vitro against the brain enzyme inhibits brain PTK as well as placental PTK-2, but has no effect against PTK-1 or pp60src. It thus appears that these three enzymes are distinct entities that differ from each other both kinetically and immunologically. With synthetic tyrosine-glutamic acid polymers as a substrate, protein tyrosine kinase activity can be detected in crude extracts of membranes.