Sequence and characterization of the sperm‐specific protein φ3 from Mytilus californianus

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Abstract
We have shown that the sperm-specific protein .vphi.3 from Mytilus californianus (Conrad) exhibits compositional microheterogeneity. For the first time, we have isolated and characterized the three major components of this protein. These fractions display different electrophoretic mobilities on Triton/urea/acetic acid polyacrylamide gels. However, they have a very similar molecular mass of 5.+-. 0.1 kDa as measured by sedimentation equilibrium in the analytical ultracentrifuge. All of them show a marked trend towards aggregation. We have also established the sequence for each of these three fractions. The sequencing data suggest an even greater extent of microheterogeneity for this protein. The predicted secondary structure from the sequences, as well as infrared analyzes carried out on the native protein, suggest an structure organization into an .alpha. helix.