Endogenous protein phosphorylation in chick and rat brain synaptic membranes

Area of Science:

• Neuroscience
• Biochemistry
• Molecular Biology

Background:

• Synaptic membranes contain crucial protein kinases involved in neuronal signaling.
• Understanding species-specific differences in these kinases can elucidate evolutionary adaptations in brain function.

Purpose of the Study:

• To compare the endogenous protein kinase activities in avian (chick) and mammalian (rat) brain synaptic membranes.
• To investigate the modulation of these kinase activities by cyclic adenosine monophosphate (cAMP) and Ca2+/calmodulin.

Main Methods:

• Preparation of synaptic membranes from chick and rat brains using an identical procedure.
• Assay of protein kinase activities using effector molecules like cAMP and Ca2+ in the presence or absence of calmodulin.
• Analysis of phosphoprotein profiles and molecular weights.
• Assessment of inhibition by phenothiazines and other compounds.

Main Results:

• Both chick and rat synaptic membranes showed similar responses to cAMP and Ca2+, with specific Michaelis constants (Kapp) for each effector.
• Chick membranes had significantly less cAMP-dependent protein kinase activity (57% less) but more Ca2+-dependent, calmodulin-requiring protein kinase activity (65% more) than rat membranes.
• Species-specific differences were noted in the molecular weights and presence/absence of certain phosphoproteins, including MAP2, Protein Ib, and B50.
• Phenothiazines, dibucaine, and adrenocorticotropin inhibited Ca2+-dependent, calmodulin-requiring protein kinase activity.

Conclusions:

• Endogenous calmodulin modulates Ca2+-dependent protein kinase activity in synaptic membranes.
• Significant species-specific differences exist in the quantitative levels and substrate specificities of protein kinases in avian and mammalian brains.
• These differences may reflect distinct roles of these kinases in neuronal function across species.