Treatment of demembranated sea-urchin sperm for 1–2 min with 10 microM-N-ethylmaleimide (Mal-NEt) at pH 8.0 prior to reactivation with 1 mM-ATP causes the asymmetry of the flagellar waveform to become desensitized to the presence or absence of Ca2+ in the reactivating medium. In such sperm, changes in concentration of free Ca2+ between 10(−7) M and 10(−3) M have no effect on the asymmetry of the waveforms as measured by the turning rate of the sperm in radians per beat cycle, while the beat frequency and the propulsive efficiency of the waves remain unchanged from the values observed in control preparations not treated with MalNEt. A somewhat more prolonged treatment with MalNEt causes a progressive decrease in the bend angles of the flagellar waves, while the beat frequency and the wavelength still remain largely unchanged. Further extension of the treatment with MalNEt causes complete loss of motility. Little ATP-induced sliding of the doublet tubules is observed upon treatment with trypsin of sperm flagella that have been rendered non-motile with MalNEt. However, the preparations of solubilized dynein 1 obtained by 0.6 M-NaCl extraction of axonemes treated with MalNEt appear almost identical to those obtained from untreated axonemes, both in terms of the amount solubilized and in the specific ATPase activities of their latent and Triton-activated forms. These preparations also appear capable of restoring much of the beat frequency of dynein-1-depleted flagella. These results suggest that the observed desensitization to Ca2+ and decrease in bend angle result from the reaction of MalNEt with axonemal polypeptides that are not part of the dynein 1 particle extracted with 0.6 M-NaCl. The rate of ATP hydrolysis by demembranated sperm rendered non-motile with MalNEt remains relatively high, and it decreases about 50% when the flagella are broken by brief homogenization. This ‘homogenizer-sensitive’ ATPase activity appears to be derived from some flagellar regulatory mechanism, which controls the ATPase activity of intact non-motile axonemes.

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