Boar Acrosin, II: Amino Acid Composition, Amino Terminal Residue and Molecular Weight Estimations by Ultracentrifugation

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Abstract
The molecular weight of boar acrosin (EC 3.4.21.10) in neutral solution was estimated to be 41,000 .+-. 1000 by high-speed sedimentation equilibrium analysis. This result agrees with the value found earlier (Schleuning et Fritz, 1974) by sodium dodecylsulfate polyacrylamide gel electrophoresis. The sedimentation coefficient of acrosin obtained by active enzyme centrifugation of partly purified preparations is in accordance with the sedimentation coefficient of the pure preparation estimated by conventional sedimentation velocity analysis. The sedimentation coefficient of acrosin is considerably decreased in slightly acidic solution (pH 4), indicating that changes in the tertiary structure occur upon acidification. The amino acid composition of the acrosin preparation homogeneous by electrophoretic and chromatographic criteria and in sedimentation studies was determined. Valine was found as the unique N-terminal amino acid. In microheterogeneous forms of acrosin, alanine and methionine were also detected in end group analysis.