B‐band protein in sea urchin sperm flagella

A high‐molecular‐weight polypeptide, named B‐band, was partially purified from sea urchin sperm flagella using selective extraction, hydroxylapatite chromatography, and sucrose density gradient centrifugation. The molecular weight of the B‐band was 440,000 by continuous system of sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE). Sedimentation coefficient of the B‐band protein was 10.5 S, and its Stokes radius was 10 nm. When examined by low‐angle rotary shadowing electron microscopy, this molecule appeared to be composed of four globular heads and two curved linkers (“double headphone shape”), which was quite different from the shape of 21 S dynein, the outer arm dynein. Flagellar axonemes were also subjected to several chemical dissections. The B‐band was not extracted with treatments that remove both arm structures but was solubilized with treatments that extract other components such as radial spokes and nexin links. The B‐band protein in the axoneme was also more susceptible to trypsin digestion than the arm structures. These results suggest that the B‐band protein is a “double headphone‐shaped” component of the axonemal structures and makes up the elastic structure that might regulate the active sliding between adjacent doublet microtubules.