Tropomyosin, a 70-kd muscle protein, sediments more slowly than does hemoglobin (65 kd). Their sedimentation coefficients are 2.6 S and 4.31 S, respectively. Which structural feature of tropomyosin accounts for its slow sedimentation?
a) Compact globular structure
b) Extended fibrous structure
c) Hydrophobic interactions
d) Disulfide bond formation