Identification and quantification of calcium-binding proteins in squid axoplasm.
The identities and quantities of calcium-binding proteins were determined in axoplasm isolated from the squid giant axon. 45Ca-binding assays on nitrocellulose filters containing axoplasm proteins separated by SDS-polyacrylamide electrophoresis revealed 4 major calcium-binding bands. These included the high-molecular-weight (Mr greater than 330 and 220 X 10(3] neurofilament proteins, an unidentified protein band that migrated around Mr 55,000, and a diverse group of proteins that migrated together around Mr 17,000. The low-molecular-weight (Mr 17,000) calcium-binding proteins could be resolved into calmodulin (ca. 120 mumol/kg axoplasm), 2 other Mr 17,000 calcium-binding proteins, and a small amount of calcineurin B. It is estimated that these calcium-binding proteins in squid axoplasm could theoretically bind about 1 mmol Ca2+/kg axoplasm. 125I-Calmodulin overlay and Western blot analyses disclosed a number of calmodulin-binding proteins in axoplasm. These included fodrin, calcineurin A, and Ca2+/CaM protein kinase II subunits.
Krinks
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MH
Laboratory of Biochemistry, National Cancer Institute, Bethesda, Maryland 20982.
Klee
C B
CB
Pant
H C
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Gainer
H
H
D000818:Animals; D001369:Axons / Q000648:ultrastructure*; D019703:Calcineurin; D002132:Calcium Radioisotopes; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D002148:Calmodulin-Binding Proteins / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D049832:Decapodiformes / Q000378:metabolism*; D007457:Iodine Radioisotopes; D008970:Molecular Weight; D010749:Phosphoprotein Phosphatases / Q000378:metabolism
D002132:Calcium Radioisotopes; D002135:Calcium-Binding Proteins; D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D007457:Iodine Radioisotopes; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases