Three distinct patterns of inhibition of MgATP 2 "-activated flagellar motility have been found by measuring the motility of Triton-demembranated sea-urchin spermatozoa beating with their heads attached to a glass surface. Inhibition of beat frequency by the reaction products, ADP and P,, is competitive with the normal substrate, MgATP 2 ", and the inhibitory effects are similar to a reduction in MgATP 2 " concentration. Inhibition of beat frequency by ATP ' 1 " is competitive with MgATP 2 ", but is accompanied by an inhibition of bending, as measured by the angle between the straight regions on either side of a bend, which is not seen when MgATP 2 " concentration is reduced. Inhibition of beat frequency by Mg a+ is not competitive with MgATP 2-, and is accompanied by an increase in bend angle, so that there is no change in the rate of sliding between flagellar tubules. These differences suggest unexpected complexity of dynein ATPase action in flagella. The beat frequencies of both swimming and attached spermatozoa show a linear double reciprocal dependence on MgATP 2 ~ concentration, with identical slopes. The calculated sliding velocities between tubules also give linear relationships, but the slopes are different, suggesting that beat frequency may be the more fundamental dependent variable in this system
To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.