title: Calcium-binding proteins in electroplax and skeletal muscle. Comparison of the parvalbumin and phosphodiesterase activator protein of Electrophorus electricus.
abstract: A soluble calcium-binding protein has been isolated from the red skeletal muscle of the electric eel (Electrophorus electricus). The purification procedure involved ammonium sulfate precipitation, gel filtration on Sephadex G-75 in the presence of 45Ca2+, and chromatography on QAE-Sephadex. This procedure resulted in the isolation of a protein which was homogeneous upon polyacrylamide gel electrophoresis. The calcium-binding protein was found to be a typical parvalbumin by the following criteria: (1) molecular weight of 11 000; (2) pI of 4.7; (3) 1.9 mol Ca2+ bound per mol protein; Kd of approx. 10(-7) M; (4) no detectable phosphorus; (5) amino acid composition included nine residues of phenylalanine, single arginine, and no tyrosine or tryptophan; (6) ximax at 259 nm; (7) 260 nm:280 nm absorbance ratio of 4.78. Only one parvalbumin could be detected in muscle. Immunoprecipitation assay revealed that the parvalbumin was a major soluble component of skeletal muscle (0.10 mg/mg soluble protein), but could not be detected in liver, kidney, brain, spleen, heart or electroplax. Comparison of the parvalbumin with a calcium-binding protein previously isolated from electroplax revealed that the two proteins were different as judged by a variety of chemical criteria. These results suggest that during embryological development of electroplax the parvalbumin is lost and that it is not required for the function of electric tissue.
mesh_terms: D000418:Albumins / Q000378:metabolism*; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D004557:Electric Organ / Q000378:metabolism*; D004593:Electrophorus; D004789:Enzyme Activation; D005779:Immunodiffusion; D007700:Kinetics; D008970:Molecular Weight; D009124:Muscle Proteins / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009928:Organ Specificity; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D011485:Protein Binding
chemical_list: D000418:Albumins; D000596:Amino Acids; D009124:Muscle Proteins; D009419:Nerve Tissue Proteins; D010727:Phosphoric Diester Hydrolases; D002118:Calcium