A putative mouse oocyte maturation inhibitory protein from urine of pregnant women: N-terminal sequence homology with human nonsecretory ribonuclease.

A putative mouse oocyte maturation inhibitory protein was purified from a urine preparation from pregnant women by Sephadex G-100 gel filtration and reverse-phase chromatography on the basis of inhibitory activity of polar body formation of denuded mouse oocytes in culture. Amino terminal sequence analyses showed that residues 5 to 15 of this protein were identical to residues 1 to 11 of human nonsecretory ribonuclease. Furthermore, residues 1 to 4 of this protein were identical to residues -4 to -1, corresponding to part of a signal peptide region of eosinophil-derived neurotoxin, whose mature sequence is identical to nonsecretory ribonuclease. These results indicate that the protein purified as a putative mouse oocyte maturation inhibitory protein from the urine of pregnant women may be a product of an peculiar processing of a nonsecretory ribonuclease precursor.