A developmental study of protein phosphorylating systems stimulated by phorbol dibutyrate in micro-slices of rat brain.

Age-dependent changes in the activity of protein phosphorylating systems stimulated by phorbol dibutyrate (M(r) range 40-80 kDa) were studied in micro-slices from rat brain labelled with [32P]orthophosphate. In adult animals phorbol stimulated the phosphorylation of the known substrates of protein kinase C (B-50/GAP-43 and MARCKS) and 3 unknown polypeptides: a basic molecule of 74 kDa (pp74B) and acidic molecules of 60 kDa (pp60A) and 42 kDa (pp42C). In neonatal animals the labelling of MARCKS was relatively very high as previously reported. Labelling of pp60A was present at birth, but increased during development; labelling of pp74B was only detected after days 8-10. The activity of the system labelling pp42C was very high during the first 2 weeks postnatal and then declined rapidly. The labelling of pp74B was considerably higher in slices from the cerebral cortex compared with the hippocampus; no regional differences in the labelling of pp60A were observed. Compared to B-50/GAP-43 and MARCKS, stimulation of phosphorylation of pp74B and pp60A required a higher concentration of phorbol. The substrates of all the phorbol-responsive systems, with the exception of pp74B, were soluble in 40% acetic acid. The possible identity of pp60A, pp74B and pp42C is discussed.