Studies on Sulfhydryl Groups during Cell Division of Sea Urchin Egg V. Change in contractility of the thread model in relation to cell division

The contractility of the thread model prepared from the KCIsoluble proteins of the egg and in vivo factors for the contraction are investigated in Hemicentrotus, Anthoddaris, and Pseudocentrotus eggs. The contractility of the thread model induced by metal ions or cystine changes during development in the characteristic pattern of high at the metaphase and low at the monaster and the interkinetic stages. The change in contractility is paralleled by the change in the ---SH content of the protein. The water-soluble fraction of the eggs has activity in causing contraction of the thread model. This activity changes during development in the same way as the contractility itself. The contraction of the thread induced by the watersoluble fractions is accompanied by a decrease in the -SH content of the thread. The activity of the water-soluble fraction in inducing the contraction is proportional to its ability to decrease the number of -SH groups. On boiling, the activity is largely destroyed. The activity is due to two components, one being non-dialyzable and the other dialyzable. Separately each component has little effect, but when mixed, the activity of the original sample is completely restored. In the preceding paper (4), a report was made that the KCl-soluble and waterinsoluble proteins of the sea urchin egg could be made into a thread model which contracted on addition o f S H oxidants or metal ions. On the other hand, the ratio of protein-bound S H groups to protein-N (SH/N) of the