Cysteine proteinase inhibitor levels in semen.

New proteinase inhibitors have recently been found in seminal plasma which specifically inhibit cysteine proteinases such as ficin, papain, cathepsin H and cathepsin B. The inhibitors consist of two components, In-A and In-B, both of which are effective in native semen. In the present work, a method of assay is devised to determine activities of both components separately. Under conditions in which In-B is denatured completely while In-A is not, inhibitory activity of In-A alone is determined. The mean In-A inhibitory level is 1.52 +/- 0.28 inhibitor unit/mL and the level is independent of the number of spermatozoa. In-B level is calculated by subtracting In-A level from the total ficin inhibition level of the semen. The mean In-B level is 1.47 +/- 0.52 inhibitor unit/ml. In-B level has a tendency to increase with increasing number of spermatozoa. The correlation coefficient is 0.307 and statistical significance p less than 0.005.