STUDIES ON SULFHYDRYL GROUPS DURING CELL DIVISION OF SEA URCHIN EGG : III. —SH Groups of KCl-Soluble Proteins and Their Change during Cleavage

Sea urchin egg proteins extracted with KCl are mostly TCA-soluble and, conversely, those extracted with TCA are KCl-soluble. Both groups are water-insoluble and show fluctuations in—SH content during the division cycle. The fluctuation of the—SH groups of the KCl-soluble protein of the whole egg is due to a —SH⇌—S—S— interchange within the freely reacting groups and not within the sluggish and masked —SH groups of the protein. The —SH content of the KCl-soluble protein of the egg cortex also fluctuates in a similar way.