title: Laser-light scattering diffusion measurements on brain microtubule protein from dogfish (Squalus acanthus) and beef.
abstract: Laser photon correlation spectroscopy and analytical ultracentrifugation were used to compare the equilibrium properties of disassembled, assembly-competent, brain microtubule protein from dogfish (Squalus acanthus) and beef. Analytical ultracentrifugation confirmed that assembly-competent bovine material at 4 degrees C, purified in the presence of glycerol through 2 cycles of assembly and disassembly, consisted of 6 S (dimer) and 35 S (ring) components, whereas assembly-competent dogfish material prepared in the same way was composed primarily of 6 S protein. By means of photon correlation spectroscopy, z-average diffusion coefficients (D'20, w) of 0.55 (+/- 0.04) x 10(-11) m2 s-1 (beef) and 1.27 (+/- 0.11) x 10(-11) m2 s-1 (dogfish) were measured at 4 degrees C for the twice-cycled assembly competent microtubule protein. Although D'20, w values for dogfish material are significantly higher than those for beef, they depart from the calculated value of 5.0 x 10(-11) m2 s-1 for a pure 6 S (dimer) solution. Microtubule accessory proteins were detectable on sodium dodecyl sulphate/polyacrylamide gels of dogfish microtubule protein. By fitting photocount autocorrelation functions to a 2-particle (dimer-ring) model it was estimated that the presence in a solution of assembly-competent dogfish microtubule protein of less than 1 ring per 250 dimers could account for the measured z-average diffusion coefficient. The temperature sensitivity of D'20, w showed that dogfish brain microtubule protein polymerized at lower temperatures than samples prepared by the same methods from beef brain.
mesh_terms: D000818:Animals; D001923:Brain Chemistry; D002417:Cattle; D002499:Centrifugation, Density Gradient; D004058:Diffusion; D004284:Dogfish; D004591:Electrophoresis, Polyacrylamide Gel; D007834:Lasers; D012542:Scattering, Radiation; D013696:Temperature; D014404:Tubulin
chemical_list: D014404:Tubulin