THE CYTOSKELETAL SYSTEM OF NUCLEATED ERYTHROCYTES .2. PRESENCE OF A HIGH MOLECULAR-WEIGHT CALMODULIN-BINDING PROTEIN

Calmodulin was detected in dogfish erythrocyte lysates by means of phosphodiesterase activation. Anucleate dogfish erythrocyte cytoskeletons bound calmodulin. Binding of calmodulin was Ca-dependent, concentration-dependent and saturable. Cytoskeletons consisted of a marginal band of microtubules containing primarily tubulin and transmarginal band material containing actin and spectrinlike proteins. Dogfish erythrocyte ghosts and cytoskeletons contained a Ca-dependent, calmodulin-binding protein (CBP) on 2 independent techniques: 125I-calmodulin binding to cytoskeletal proteins separated by SDS-PAGE [sodium dodecyl sulfate-polyacrylamide gel electrophoresis] and in situ azidocalmodulin binding in whole anucleate ghosts and cytoskeletons. CBP, with an apparent MW of 245,000, comigrated 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 appears to be localized in the transmarginal band material and not in the marginal band. Similarities between CBP and high MW calmodulin-binding proteins from mammalian species are discussed.