A latent activity dynein-like cytoplasmic magnesium adenosine triphosphatase.

A MgATPase has been isolated and characterized from unfertilized sea urchin eggs which is very similar, but not identical, to latent activity axonemal dynein. The cytoplasmic MgATPase activity sediments at 20 S, slightly slower than 21 S latent activity flagellar dynein. Activity is stimulated by nonionic detergent and is inhibited by sodium orthovanadate but is not as sensitive to vanadate as is 21 S flagellar dynein. The egg 20 S MgATPase is composed, at least in part, of three high molecular weight polypeptides. In addition, two intermediate-sized polypeptides appear to co-sediment with the 20 S MgATPase activity. A novel microtubule-affinity assay reveals that high molecular weight polypeptides 1 and 2 of the egg 20 S MgATPase can bind to reassembled microtubules and can be released from the microtubules with MgATP2-. Further, the apparent specific activity of the egg MgATPase is enriched 15-fold by a single microtubule binding step. The results suggest that the cytoplasmic 20 S MgATPase is a dynein-like microtubule translocator which resides in the unfertilized egg awaiting future incorporation onto microtubules in order to perform work. The egg 20 S enzyme might function in cytoplasmic microtubule-mediated movement or it might be a precursor of embryonic ciliary dynein.