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pubmed:abstractText |
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.
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