PROTEIN PHOSPHORYLATION IN SYNAPTIC MEMBRANES REGULATED BY ADENOSINE 3′:5′‐MONOPHOSPHATE: REGIONAL AND SUBCELLULAR DISTRIBUTION OF THE ENDOGENOUS SUBSTRATES

Abstract

Abstract— The aim of these studies is the determination of the topographic distribution of the endogenous substrates in synaptic membrane preparations susceptible to phosphorylation in reactions modulated by adenosine 3′:5′‐monophosphate or Ca 2+ . To this end we have investigated the distribution of these phosphosubstrates in different cellular and synaptic subfractions obtained from rat cortex and corpus striatum, in other rat brain regions and in bovine retina, as well as membrane fractions from liver and testis. The results obtained indicate that two cAMP‐dependent protein substrates B (p80, i.e. apparent M R = 80,000) and C (p75) are, as originally suggested by G reencard and collaborators confined to nerve tissue; they are located at least in part in the postsynaptic density, as is an additional protein D (p66). This localization appears to be shared by a cAMP‐dependent, and a cAMP‐independent entity, designated E (p54) and p48, respectively. In contrast, at least one prominent protein substrate requiring cAMP for its phosphorylation, component F (p50), appears to be associated predominantly with the postsynaptic membrane. At least two of these cAMP‐dependent (B and C), as well as two Ca 2+ ‐dependent (p63 and p59), phosphoproteins appear to be associated with the presynaptic membrane.