Identification and purification of an aspartic proteinase from human semen

To purify and evaluate the molecular changes associated with an aspartic protease (Cathepsin D) in human semen from infertile subjects. Cathepsin D was purified from normo-, oligo- and azoospermic semen, by a procedure involving detergent solubilisation, affinity chromatography and gel filtration chromatography. The enzyme from normo-, oligo- and azoospermic samples was purified 86, 60 and 44 fold respectively. The purified enzyme appeared as a single band on SDS as well as on native PAGE irrespective of the pathological conditions. The molecular weight of Cathepsin D from oligospermic and normospermic samples was 40 kDa while that of azoospermic sample was found to be 43 kDa. The enzyme was inhibited by pepstatin while other proteinase inhibitors and metal ions did not have any effect. Purified Cathepsin D from azoospermic sample differs from normospermia and oligospermia.