Chemical heterogeneity of protofilaments forming the outer doublets from sea urchin flagella

Upon subjecting isolated outer doublets from S. purpuratus sperm tails to heat and increasing concentrations of detergent Sarkosyl (SLS), the microtubules are partially solubilized. Electron microscopy shows that the B tubule is solubilized at 37 °C or low SLS concentrations; solubilization of tubule A requires higher temperature (60 °C). High concentrations of SLS solubilize parts of the A tubule until only a detergent-resistant fraction composed of three protofilaments is left. Solubilized and unsolubilized fractions contain the same two major protein components (α and β) as do the untreated outer doublets when examined by gel electrophoresis. The ratio of the two components throughout the extraction sequences remains 1:1 ± 0.1 as determined on the basis of dye binding.