Boar acrosin is a two-chain molecule. Isolation and primary structure of the light chain; homology with the pro-part of other serine proteinases

Acrosin (EC 3.4.21.10), the major proteinase of mammalian spermatozoa, has been demonstrated to be a two-chain glycoprotein with an Mr-4200 light chain covalently attached to an Mr-37000 heavy chain. Following mercaptolysis of the disulfide bonds, the two chains were separated by high-performance liquid chromatography on a reversed-phase column. Sequence analysis of the isolated light chain (23 amino acid residues) indicated a considerable sequence homology with the bovine chymotrypsinogen activation peptide (6 out of 15 positions with identical amino acids, i.e. 40% identity) and the pro-part of other serine proteinases (17-22% identity), thus suggesting that the acrosin light chain corresponds to the pro-part of the acrosin zymogen. In position 3, the light chain confers a carbohydrate side chain N-glycosidically linked to the acceptor sequence Asn-Xaa-Thr. Evidence is presented that the acrosin light chain is connected via two disulfide bridges to the heavy chain which contains about 320 amino acids including the active-site residues of the proteinase.