Tyrosine Protein Kinases in Membrane Fractions from Rat Cerebral Cortex1

Specific activities of tyrosine tubulin kinase in the participate fractions from rat cerebel-lum, medulla oblongata, hypothalamus, striatum, midbrain, and cerebral cortex ranged within 30 % of each other and more than 3 times higher than those in the soluble fractions. In the cerebral cortex, tyrosine protein kinase activity toward tubulin and tyrosine-glutamate (1: 4) copolymers was mainly distributed in the plasma membrane and the microsome fractions. The kinase activity in cerebral cortex particulate fractions was quantitatively solubilized and separated into two peaks, kinase I and kinase II, by Sephacryl S-300 gel filtration in the presence of 0.2 % Nonidet P-40 and 0.2 M NaCl. Kinases I and II were each resolved into 5 active peaks (I-l->5 and II-l-»5) by casein-Sepharose column chromatography. The molecular weights of these kinases were estimated from the «2o,w values to be 59,000-65,000. The Km values of II-l->5 for tubulin were nearly 10 times higher than those of 1-1—>5. However, the Km values of the two groups of kinases for tyrosine-glutamate copolymers were not so significantly different. About 60 % of the copolymers kinase activity in 1-3, 1-4, II-3, and II-4 was immunoprecipitable with a saturating amount of monoclonal antibody against pp60 c s r c. Incubation of the immuno-precipitates with ATP resulted in the autophosphorylation of a 60 kDa protein in 1-3 an