Preparation and Characterization of the Major Isotype of Parvalbumin from Skeletal Muscle of the Toad (Bufo bufo japonicus)

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The major isotype of parvalbumin has been isolated from the skeletal muscle of the toad, Bufo bufo japonicus. Unlike the skeletal muscle of every frog so far examined (Rana esculenta, Rana temporaria, and Rana catesbeiana), which contains two major isotypes of parvalbumins, toad skeletal muscle has been shown to contain only one isotype, but the content of parvalbumin in toad skeletal muscle was similar to the sum of those of the two isotypes in skeletal muscles of frogs. This feature of toad skeletal muscle is advantageous to clarify the physiological role of parvalbumin. The relative molecular mass of toad parvalbumin was estimated to be 12, 200 by SDS-polyacrylamide gel electrophoresis. The isoelectric point was determined to be 4. 81 by polyacrylamide gel isoelectric focusing. The amino acid composition indicated that toad parvalbumin corresponds to bullfrog (R. catesbeiana) pI 4. 97 parvalbumin, showing that toad parvalbumin is genetically an a-parvalbumin. It was also revealed by the amino acid composition that toad parvalbumin is distinctly different from any of the parvalbumins from frogs. The ultraviolet spectrum of toad parvalbumin is consistent with its amino acid composition. The ultraviolet differ-ence spectrum of the Ca²⁺-loaded form vs. the metal-free form indicates that some Phe residues in the toad parvalbumin molecule are affected by a conformational change associated with Ca²⁺ binding. On electrophoresis in polyacrylamide gel in 14 mM Tris and 90 mM glycine, the metal-free and Mg²⁺-loaded forms of toad parvalbumin migrated twice as fast as the Ca²⁺-loaded form. The fact that toad parvalbumin shows decreased mobility in the Ca²⁺-loaded form is similar to the cases of bullfrog parvalbumins or calmodulin but is different from the case of tropo-nin C.