A protein kinase C inhibitory activity is present in rat brain homogenate

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Abstract
The partial purification and characterization of (a) factor(s) from rat brain which inhibit(s) the activity of calcium and phospholipid-dependent protein kinase from the same tissue is described. This factor, present in 100000 × g rat brain homogenate supernatant, is inactivated upon treatment by trypsin and pepsin and is therefore assumed to be a protein. It was partially purified by ion-exchange chromatography on DEAEcellulose, ammonium sulfate precipitation and gel filtration. This inhibitor is not stable to heating at 70°C for 10 min, however partial renaturation of the inhibitory activity can be observed after incubation of the denatured inhibitor for 24 h at 4°C. It is precipitable by 10% trichloroacetic acid and by 2 M ammonium sulfate. It exhibits a Stokes radius of 20 Å by gel exclusion chromatography, corresponding to a molecular mass of 20 kDa assuming a globular shape. Kinetic analysis of the inhibition of calcium-phospholipid-dependent histone kinase activity indicates that the inhibitor is competitive with respect to the protein substrate. No change was observed in the kinetic values of the kinase for ATP, Ca2+ and phospholipids