Purification and characterization of a 32-kDa protein that localizes to the sea urchin extraembryonic matrix, the hyaline layer.

We have purified a 32 kilodalton (kDa) protein that localized with isolated, intact hyaline layers prepared from 1-h-old embryos. The protein appeared not to bind calcium and was not quantitatively released from 1-h-old embryos in the absence of Ca2+ and Mg2+. Using polyclonal antiserum prepared against the 32-kDa protein, the antigen was detected throughout embryonic development. By the hatched blastula stage of development, the 32-kDa protein was replaced by a species of slightly smaller molecular mass. Quantitative determination indicated that the 32-kDa protein accounted for approximately 6% of the total protein present in the sea urchin egg. This result is suggestive of a structural role for the 32-kDa protein that is required throughout embryonic development, although perhaps in a modified form from the hatched blastula stage on.