Ca2+ and cyclic AMP regulate phosphorylation of same two membrane-associated proteins specific to nerve tissue

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Cyclic adenosine monophosphate (cAMP) was previously shown to stimulate the phosphorylation of nerve-specific proteins Ia and Ib in synaptic membranes.
• Calcium (Ca2+) and veratridine were observed to stimulate phosphorylation of proteins with similar molecular weights in synaptosomes.

Purpose of the Study:

• To determine if the proteins phosphorylated by Ca2+/veratridine in synaptosomes are identical to proteins Ia and Ib phosphorylated by cAMP in synaptic membranes.
• To investigate the regulatory roles of Ca2+ and cAMP in protein phosphorylation.

Main Methods:

• Comparative analysis of protein phosphorylation in synaptic membranes and synaptosomes.
• Extraction and characterization of phosphorylated proteins.
• Digestion with collagenase and three other proteolytic enzymes.
• Analysis of phosphopeptide molecular weights.

Main Results:

• Proteins phosphorylated by both Ca2+/veratridine and cAMP exhibited similar apparent molecular weights and charges.
• Both sets of proteins were digested by collagenase to identical intermediates and end products.
• Digestion with three other enzymes yielded phosphopeptides of similar molecular weights.

Conclusions:

• Calcium (Ca2+) and cAMP can independently regulate the phosphorylation of proteins Ia and Ib.
• The findings indicate that Ca2+ and cAMP converge on the same phosphorylation targets in nerve tissue.