Regional variations in protein phosphorylating activity in rat brain studied in micro-slices labeled with [32P]phosphate.

Regional variations in protein phosphorylating activity in the rat brain were studied. Micro-slices (1 mm diameter) were prepared from 19 brain areas, phosphoproteins labeled by incubation with [32P]phosphate, and the tissue analyzed by nonequilibrium two-dimensional electrophoresis and autoradiography. Attention was focused on three phosphorylating systems that showed consistent variation in activity. (1) A system that phosphorylates a substrate of 47 kDa (ppH-47) whose activity was highest in the hippocampus. The next highest activity of this system was observed in the globus pallidus, followed by the periventricular gray matter of the aqueduct, lateral septum, cerebellar cortex, entorhinal cortex, hypothalamus, mammillary nuclei, amygdala, and substantia nigra. Activity was low or undetectable in the cerebral cortex, neostriatum, and the colliculi. (2) A system that phosphorylates a substrate of 50 kDa (ppC-50) whose activity was highest in the caudate nucleus. The activity of this system was roughly inversely correlated with that of the ppH-47 system. (3) The protein kinase C system that phosphorylates an 82- to 87-kDa substrate known as MARCKS. The highest activity of this system was observed in the cerebellar cortex, followed by the hypothalamus, mammillary nuclei, periventricular gray matter of the aqueduct, and the superior colliculus. Activity of this system was relatively low in several regions of the cerebral cortex, the neostriatum, and the inferior colliculus.