Studies on sulfhydryl groups during cell division of sea urchin egg. IV. Contractile properties of the thread model of KLCl-soluble protein from the sea urchin egg.

A KCl-soluble protein fraction can be extracted from the water-insoluble residue of the homogenate of sea urchin eggs which contains three major components separable by ultracentrifugation. When the extract is stirred in acetone or distilled water, a fibrous precipitate appears which has a strong birefringence positive in the direction of the long axis. When the fraction is squirted through a slender tubing, it precipitates in the form of a thread. The thread model contracts vigorously under the action of di-, tri-, and tetravalent metal ions; the contraction can be reversed by EDTA. The contraction and the elongation of the thread model can be repeated many times. The thread model contracts also in the presence of dehydroascorbic acid, cystine, oxidized glutathione, or other oxidizing agents, and this contraction is reversed by reducing agents such as cysteine or ascorbic acid. When -SH groups of the thread model are blocked by various -SH reagents, the contraction by metal ions is inhibited to some extent. As mechanisms of the contraction, electrostatic forces between metal ions and negative charges of the thread model are essential for metal ion-induced contraction and oxidation of -SH groups of the thread model for the contraction by oxidizing reagents.