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J. Biochem, 1986, Vol. 99, No. 5 1353-1358
© 1986 Japanese Biochemical Society

research-article

Calmodulin-Binding Protein (55K+17K) of Sea Urchin Eggs Has a Ca2+– and Calmodulin-Dependent Phosphoprotein Phosphatase Activity1

Fuyuki IWASA*,2 and Koichi ISHIGURO**,3

*Department of Biology, The University of Tokyo komaba, Meguro-ku, Tokyo 153
**Department of Biophysics and Biochemistry, The University of Tokyo Hongo, Bunkyo-ku, Tokyo 113

A calmodulin-binding protein from sea urchin eggs consisting of two subunits (55 and 17K-daltons) was identified as a Ca2+-dependent phosphoprotein phosphatase similar to calcineurin in mammalian brain and to phosphatase 2B in skeletal muscle. Peptide mappings showed that the 55K subunit was different from 61K subunit of calcineurin, whereas the 17K subunit was similar to 19K subunit of calcineurin but different from calmodulin. The 55K+ 17K protein of sea urchin eggs dephosphorylated 32P-inhibitor-1 in a Ca2+- and calmodulin-dependent manner. Vmax and Km for inhibitor-1 in the presence of Ca2+ and calmodulin were 2,100 pmol P1/min/mg and 2.7/µM. Ca2+ phosphatase activity for inhibitor-1 was detected in homogenates of both unfertilized and fertilized eggs, but was not detected in isolated cortices and mitotic apparatus.

1This work was supported in part by a Grant-in-Aid for Scientific Research (No. 58340041) from the Ministry of Education, Science and Culture to Dr. H. Mohri, The University of Tokyo.

2Present address: Suntory Institute for Biomedical Research, Wakayamadai 1-chome, Shimamoto-cho, Osaka 618.

3Present address: Mitsubishi-Kasei Institute of Life Sciences, Minami-Ooya, Machida, Tokyo 194.


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