Calmodulin was detected in dogfish erythrocyte lysates by means of phosphodiesterase activation. Anucleate dogfish erythrocyte cytoskeletons bound calmodulin. Binding of calmodulin was calcium-dependent, concentration-dependent, and saturable. Cytoskeletons consisted of a marginal band of microtubules containing primarily tubulin, and trans-marginal band material containing actin and spectrinlike proteins. Dogfish erythrocyte ghosts and cytoskeletons were found to contain a calcium-dependent calmodulin-binding protein, CBP, by two independent techniques: (a) 125I-calmodulin binding to cytoskeletal proteins separated by SDS PAGE, and (b) in situ azidocalmodulin binding in whole anucleate ghosts and cytoskeletons. CBP, with an apparent molecular weight of 245,000, co-migrated with the upper band of human and dogfish erythrocyte spectrin. CBP was present in anucleate ghosts devoid of marginal bands and absent from isolated marginal bands. CBP therefore appears to be localized in the trans-marginal band material and not in the marginal band. Similarities between CBP and high molecular weight calmodulin-binding proteins from mammalian species are discussed.

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