Isolation of the boar sperm acrosin peptide released during the conversion of alpha-form into beta-form

The sperm proteinase acrosin occurs in several enzymatically active forms which differ from each other in molecular mass. The high-molecular-mass alpha-form (53 kDa) is converted into the low-molecular-mass beta-form (38 kDa) by auto-proteolysis. As these two forms possess identical N-termini and identical A-chains (light chains) the difference must reside in the C-terminal parts of their B-chains (heavy chains). It could be demonstrated by gel electrophoresis that on incubation of alpha-acrosin, in addition to beta-acrosin, a main degradation product of approx. 18 kDa was formed. This fragment was isolated by gel filtration chromatography. The amino-acid composition of the fragment corresponded to the difference between that of alpha-acrosin and of beta-acrosin, and showed a strikingly high proportion of proline. It is suggested that this hydrophobic segment from the C-terminal region of alpha-acrosin accounts for the special membrane-associating property of the enzyme.