Stimulation of bull sperm hyaluronidase by polycations

The activity of bull sperm hyaluronidase (hyaluronate 3-glycanohydrolase, EC 3.2.1.36) is increased by the inclusion of polycations in the assay mixture. At pH 3.8, bovine serum albumin and histone give the greatest stimulation, while protamine sulfate, spermine, spermidine and hyamine 2389 stimulate to a lesser extent. Enzyme activity increases with serum albumin concentration to a nearly constant, high level at serum albumin concentrations greater than 1 mg/ml. Other stimulatory compounds show a similar concentration dependence except that inhibition of enzyme activity occurs at high concentrations of stimulator. The degree of stimulation depends on the pH, sample concentration and substrate concentration. Enzyme preparations with a low protein content give the greatest stimulation, while preparations with a high protein content show little stimulation. The concentration of serum albumin required for maximum stimulation increases with increased hyaluronic acid concentration. The results suggest that the stimulation of sperm hyaluronidase is nonspecific and results from an interaction of the polycation with hyaluronic acid. Since protein in the enzyme preparation substitutes for exogenous stimulator to a varying degree, serum albumin should be included in the assay mixture for sperm and testicular hyaluronidase to assure measurement of maximum enzyme activity.