Lectins induce the redistribution and internalization of receptors on the surface of cultured neurons

A cytoplasmic dynein ATPase has been identified in three species of unfertilized sea urchin eggs, Strongylocentrotus droebachiensis, S. purpuratus, and Arbacia punctulata. The enzyme was partially purified by sucrose gradient density centrifugation, and its polypeptide chain weight and composition were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The protein has enzymatic characteristics in common with flagellar dynein. It is activated nearly equally by Mg²⁺ and Ca²⁺, has no activity in the presence of K⁺ and EDTA, shows a specificity for ATP over other nucleoside triphosphates, and is inhibited by vanadate anion. On SDS-PAGE, the enzyme shows two major bands at 320,000 and 385,000 daltons, comigrating with certain ciliary and flagellar dynein polypeptides. The enzyme, given the name “egg dynein,” constitutes 2 to 4% of the total cell protein in the unfertilized egg and maintains this high value from fertilization through the late blastula stage. It appears to be equally distributed throughout the embryo at the 16-cell stage. Possible functions of egg dynein are discussed and models for dynein-microtubule mediated movements within the cytoplasm are presented.