Some properties of bound and soluble dynein from sea urchin sperm flagella

Abstract

Axonemes were isolated from sperm of Colobocentrotus by a procedure involving two extractions with 1% Triton X-100 and washing The isolated axonemes contained 7 × 10-15 g protein per µm of their length. Treatment of the axonemes with 0 5M KC1 for 30 min extracted 50-70% of the flagellar ATPase protein, dynein, and removed preferentially the outer arms from the doublet tubules. Almost all of the dynein (85-95%) could be extracted from the axonemes by dialysis at low ionic strength. In both cases the extracted dynein sedi-mented through sucrose gradients at 12-14S, and no 30S form was observed The enzymic properties of dynein changed when it was extracted from the axonemes into solution. Solubilization had a particularly marked effect on the KC1- and pH-dependence of the ATPase activity. The pH-dependence of soluble dynein was fairly simple with a single peak extending from about pH 6 to pH 10. The pH-dependence of bound dynein was more complex. In 0.1 M KCI, the bound activity appeared to peak at about pH 9, and dropped off rapidly with decreasing pH, reaching almost zero at pH 7; an additional peak at pH 10 0 resulted from the breakdown of the axonemal structure and solubilization of dynein that occurred at about this pH. A similar curve was obtained m the absence of KC1, except for the presence of a further large peak at pH 8 Measurement of the kinetic parameters of soluble dynein showed that both Km and Vmax increased with increasing concentrations of KG up to 0.5 M When bound dynein was assayed under conditions that would induce motility m reactivated sperm (0.15 M KCI with Mg++ activation), it did not obey Michaelis-Menten kinetics, although it did when assayed under other conditions. The complex enzyme-kinetic behavior of bound dynein, and the differences between its enzymic properties and those of soluble dynein, may result from its interactions with tubulin and other axonemal proteins. © 1972, Rockefeller University Press., All rights reserved.