Ontogeny of synaptic phosphoproteins in brain.

The ontogeny of two endogenous substrates for cyclic AMP-dependent protein kinase (ATP:protein phosphotransferase; EC 2.7.1.37) has been studied in rat and guinea pig cerebrum. These endogenous substrates, referred to as proteins Ia and Ib, have been shown in other studies to be specific to nervous tissue and to be enriched in the synaptic membrane and synaptic vesicle fractions of adult brain. In the present study, proteins Ia and Ib were shown to increase markedly during the time of major synaptogenesis in rat cerebrum and guinea pig cerebrum, in which the morphological development of synapses is predominantly postnatal and prenatal, respectively. Similar results were obtained either by measuring endogenous phosphorylation of proteins Ia and Ib in the synaptic membrane fraction or by measuring phosphorylation of extracted proteins Ia and Ib with added protein kinase.