Control of the Amount of a 34K Ca2+-Dependent Membrane Binding Protein (Calelectrin)

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Abstract
A 34,000-Da Ca2+-dependent membrane binding protein (34K) was purified from the electric organ of Torpedo marmorata. Specific antibodies to this protein were raised in rabbits, and radioimmunoassay was used to test the presence of 34K in different tissues of Torpedo as well as in other species. In Torpedo, not only the electric organ, but also the muscle, the spleen, and the liver contained 34K antigenicity. Blood was the only tissue in which 34K antigenicity could not be detected. A 34,000-Da protein (Mr 32,000-36,000) that bound to Torpedo acetylcholine receptor (AChR)-rich membrane in a Ca2+-dependent manner and cross-reacted with anti-(Torpedo 34K) antibody was found in chicken muscle, rat muscle, marine mollusk (Aplysia) central ganglia, and rat and human brain. The concentration of 34K seems to be controlled during development. Chicken 34K antigenicity reached a peak on embryonic day 18, declined, and finally gained its maximal value after synaptic maturation. The AChR concentration in chicken legs also changed in the course of muscle development, although it showed a peak on embryonic day 12 and then declined rapidly. In rat diaphragm, both AChRs and 34K were concentrated in the subsynaptic region. Transection of the phrenic nerve induced the synthesis of AChRs in postsynaptic muscle fibers. This operation did not increase the amount of 34K in the diaphragm. On the contrary, it reduced 34K content to the extrasynaptic level. Taken together, these results support the idea that 34K is an important structural constituent of mature synapses, an observation suggesting the involvement of this protein in the function of the mature synapse.