Studies on the glycosidases of semen: Purification and properties of α-D-mannopyranosidase from goat seminal plasma

Summary

Alpha D-mannosidase activity in goat semen was observed to be distributed in sperm and seminal plasma. In sperm the enzyme, present in soluble and bound forms, was located within the acrosome. The bound enzyme was associated with the denuded sperm. Seminal plasma α-mannosidase was purified 100-fold and the final preparation was shown to be homogeneous by polyacrylamide and SDS gel electrophoresis and on isoelectric focusing. The molecular weight of the enzyme, determined by gel filtration and disc electrophoresis in the presence of SDS, was 220,000. The isoelectric pH was 7.42 and the amino acid composition is reported.

α-Mannosidase catalyzed the hydrolysis of both synthetic and natural substrates. The K_m of p-nitrophenyl α-D-mannoside and α-methyl D-mannoside were 0.695 mm and 71.9 mm at pH 4.0, the optimum pH. The natural substrates were hydrolysed to varying degrees. Zn²⁺ was not essential though it activated the enzyme activity over longer incubations. The enzyme was observed to be more stable at wider pH range in the presence of Zn²⁺ than in its absence. EDTA which did not affect the enzyme activity has effect on enzyme stability similar to Zn.²⁺ Seminal α-mannosidase is not a zinc metalloenzyme but is activated by Zn²⁺.