Characteristics of skeletal muscle calsequestrin: comparison of mammalian, amphibian and avian muscles

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Abstract
Calsequestrin was identified in the isolated sarcoplasmic reticulum from skeletal muscle of three mammalian species (man, rat and rabbit) and from frog and chicken muscle, using electrophoretic and immunoblot techniques. It was further characterized in sarcoplasmic reticulum protein mixtures and at several stages of purification, following extraction with EDTA. We found extensive similarities in apparent molecular weight values, Stains All staining properties and in Cleveland's peptide maps, between mammalian calsequestrins, and no detectable difference within a species between fast and slow muscle. Human calsequestrin, with an apparent molecular weight of 60 000 when measured at alkaline pH and of 41 000 when measured at neutral pH, appears to be the smallest in size. Frog calsequestrin, although weakly cross-reactive with rabbit calsequestrin and having a relatively higher apparent molecular weight at alkaline pH (72 000), shares several significant properties with mammalian calsequestrins. It bound calcium with a high capacity (1300 nmol per mg protein), it contained about 32% acidic amino acid residues and focused at closely similar pI values. We observed the formation of a complex with Stains All absorbing maximally at 535 nm, rather than at 600 nm, and an even more marked shift in apparent molecular weight at neutral pH. We found distinct differences in the case of chicken calsequestrin, in addition to those previously reported. It is a highly acidic, calcium-precipitable protein, but its amino acid composition is contradistinguished by a higher ratio of glutamate to aspartate and its rate of electrophoretic mobility is minimally affected by changes in pH. It stained deep bluish with Stains All after gel electrophoresis and yielded a protein-dye complex in aqueous solution, absorbing maximally at 560 nm, and finally, it bound fluorescent Concanavalin A.