Protein phosphorylation in nervous tissue: possible involvement in nervous tissue function and relationship to cyclic nucleotide metabolism

Protein phosphorylation in human synaptosomal membranes: evidence for the presence of substrates for cyclic nucleotide guanosine 3'-5'-monophosphate dependent protein kinases

Synaptosomal membranes prepared from different anatomical regions of postmortem human brain readily incorporate phosphate when incubated with labelled ATP in vitro. Separation of proteins on SDS slab gels indicated up to 30 protein bands stained by Coomassie blue of which ten incorporated label, as detected by radioautography (mol. wt. range 16-110 K with a major double band at 49-50 K). Incorporation into the 110 K region appeared to increase in older persons, and that into the 49-50 K region decreased. Human but not rat membranes subjected to similar conditions of treatment failed to respond to the addition of cAMP at 10(-5) - 10(-7) M but were highly sensitive to the addition of cGMP at 10(-6) M, which led to intensification of existing bands and the appearance of a major band at 60 K. The 110 K band present in high concentration in white matter striatum, caudate nucleus, and putamen was insensitive to cGMP addition. The presence of cGMP-dependent protein kinase substrates has not previously been reported in synapses, and it may be of significance in view of the known sensitivity of this system to biological regulatory agents.

Cyclic nucleotides in nervous tissue

A review of the literature emphasizes that cyclic nucleotides play a key role in regulation of cell growth, differentiation and metabolism in diverse tissues and, in addition, are closely involved in neural tissue function. The role of cAMP as a second messenger is discussed.