Abstract
An acylpeptide called K-26, which was isolated from a culture filtrate of Bacillus sp. 503, inhibited motility of both live sea urchin sperm as well as Triton X-100-extracted sperm model. In each case, complete inhibition was observed at concentrations of more than 1 μM or 6 μM, respectively. This inhibitory effect of K-26 on the Triton-extracted sperm could not be reversed by reducing the concentration of K-26 in the reactivation medium containing 1 mM ATP. However, it was reversed when the ATP concentration in the reac-tivation medium was simultaneously reduced.
At concentrations below 4 μM, K-26 did not completely suppress the flagellar movement of the Triton-extracted sperm, but reduced the beat frequency in a competitive manner; the maximal beat frequency (Fmax) was 31.2 Hz whether in the absence or in the presence of 4 μM K-26, while Km for ATP was 0.19 mM or 0.28 mM, respectively. ATPase activity of isolated axonemes was increased severalfold in the presence of K-26. The sliding movement between the outer doublet microtubules in trypsin-treated axonemes was normal at K-26 concen-trations as high as 20 μM.
From these results, it was suggested that K-26 affects the mechanism that con-verts the sliding movement between the outer doublet microtubules into a ben-ding motion, and thereby inhibits the motility of the Triton-extracted sperm model.
