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The effects of zona pellucida glycoproteins, sulfated polymers and non-sulfated polymers on the activation kinetics of boar sperm proacrosin to β-acrosin have been investigated. The aim has been to understand more about the behaviour and function of this protein after it has been released from the acrosome at the time of fertilization. Purified proacrosin was allowed to autoactivate at pH 8.0 in the presence of different concentrations of homologous zona glycoproteins, sulfated polymers (fucoidan, chondroitin sulfates A, B and C, dextran sulfate, polyvinylsulfate and heparin) and non-sulfated polymers (dextran, polyvinylphosphate and hyaluronic acid). Enzyme activity was measured against N-benzoyl-L-arginine p-nitroanalide substrate and changes in molecular mass of the protein monitored by SDS-PAGE. Results show that zona pellucida glycoproteins, fucoidan, dextran sulfate and polyvinylsulfate all potentiate the conversion of proacrosin to β-acrosin but subsequently inhibit its amidase activity. Dextran, polyvinylphosphate, chondroitin sulfates A, B and C and glucose-6-sulfate, on the other hand, either have no effect on autoactivation and β-acrosin activity, or enhance it slightly. SDS-PAGE analysis confirmed these observations and further indicated that binding of sulfated polymers to proacrosin inhibited staining by Coomassie Blue. These results are consistent with the hypothesis that binding of zona pellucida glycoproteins and sulfated compounds to proacrosin/acrosin is stereospecific and that contact activation onto soluble 'surfaces' causes conformational changes that are responsible for potentiation or inhibition of activation. The implications of these findings for sperm binding and penetration of the zona pellucida are discussed.
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