Heavy metals and spermatozoan motility. III conformational changes induced by divalent cations and by ATP in flagellar proteins.

Conformational changes of flagellar proteins of sea urchin spermatozoa caused by divalent cations and nucleotides were investigated by examining the circular dichroism spectra of axonemes and outer doublet microtubules. The alpha-Helix content of the flagellar components was diminished in the presence of zinc, cadmium and mercury, while no other heavy metals contributed to such a change. The original content of alpha-helix was restored by the subsequent addition of ATP or GTP, the former being more effective. An oscillation was found to occur in the alpha-helix content measured at 222 micron in the presence of zinc and ATP. On the other hand, ATP caused a marked reduction in alpha-helical structures of axonemes in the presence of magnesium or calcium, especially in a medium containing KCl. The effect was rather specific for ATP. The obtained results were discussed in relation to the basic mechanisms of spermatozoan motility.