KAM zyx ETAI.. Biochem. 16, zyxwvutsrqp 225. Huber, R., Epp, O., and Formanek, H. (1970), J. Mol. Biol. 52, 349. Irving, H., and Williams, R. J. P. (1948), Nature (London) 162, 746. Jones, W. C., Rothgeb, T. M., and Gurd, F. R. zyxwvut I%. (1 976), J. Biol. Chem. 251, 7452. Keyes, M. (1968), Ph.D. Dissertation, University of Minne- sota. Keyes, M., Falley, M., and Lumry, R. (1971), J. Am. Chem. Soc. 93, 2035. Keyes, M., and Lumry, R. (1968), Fed. Proc.. Fed. Am. Soc. Exp. Biol. 27, 895. Keyes, M., and Lumry, R. (1 97 I ), in Probes of Structure and Function of Macromolecules and Membranes, Vol. 2, Chance, B., Yonetani, T., and Mildvan, A. S., Ed., New York, N.Y., Academic Press, p 343. Keyes, M., Mizukami, H., and Lumry, R. (1 967), Anal. Bio- chem. 18, 126. Nobbs, C. L., Watson, H. C., and Kendrew, J. C. (1966), Nature (London) 209, 339. Oelshlegel, F. J., Brewer, G. J., Knutsen, C., Prasad, A. S., and Shoomaker, E. B. (1974), Arch. Biochem. Biophys. 163, 142. Oelshlegel, F. 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Chem. 239, 4151. reveals that the dimer is a compact, slightly elongated mole- cule, and that the tetramer probably consists of two parallel dimers. On increasing the concentration of solutions containing spectrin dimers, oligomers are formed, which are not rapidly dissociated on dilution. At very low protein concentrations (below about 0.05 mg/mL) there is evidence of the onset of a rapid dissociation equilibrium between dimers and single chains. Other physical properties of the spectrin have been measured. The size and shape of the spectrin molecule would seem to rule out any major physical resemblance to myosin. Structural Study of Spectrin from Human Erythrocyte Membranes? 5568 BIOCHEMISTRY, VOL. 16, NO. 25, 1977 branes have led to the conjecture that spectrin may be structurally and functionally related to myosin (Guidotti, 1972; Brandon, 1975; Schechter et al., 1976). Arguments have been given (Gratzer and Beaven, 1975) against such a view, but there has been poor agreement between results from different laboratories, bearing on the size and shape of the molecule; one study (Schechter et al., 1976) indeed reports, in contrast to earlier work, frictional properties compatible with a very asymmetric, myosin-like particle. In addition Sheetz et al. (1976b) have reported a weak cross-reaction of spectrin with antibodies to smooth-muscle myosin (though not of myosin to antispectrin). We have undertaken a study of spectrin by hy- drodynamic methods, light scattering, and electron microscopy