Effect of Polyamines on the Activity of Acrosin and the Activation of Proacrosin1

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Abstract
Polyamines, especially spermine, were demonstrated to stimulate both the esterase activity and proteinase activity of acrosin, a critical enzyme in the fertilization process. The stimulation was demonstrated to result from an increase in the maximal velocity, with little effect on the affinity of the enzyme for substrate. Spermine also protected acrosin against autoproteolytic degradation. There was, however, no stimulation or stabilization of trypsin activity. Although polyamines stimulated the activity of acrosin, they inhibited the autocatalytic activation of proacrosin, the zymogen form of the enzyme. Spermine produced the greatest stimulation of proteinase activity and the greatest inhibition of proacrosin activation. This is the first report of polyamine stimulation of a proteolytic enzyme and inhibition of zymogen activation. These results suggest that polyamines could serve as in vivo modulators of the proteolytic activity of acrosin and the activation of proacrosin.

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