Purification and partial peptide sequence analysis of the boar 32 kDa sperminogen

Boar 32 kDa sperminogen was purified from acid extracts of washed epididymal spermatozoa, and partial peptide sequence was determined. Boar sperminogen was purified from the acid extracts of boar spermatozoa by gel filtration through Sephadex G-75 column, followed by preparative SDS-PAGE. Gelatin zymographic analysis of the gel-filtered fractions showed that sperminogen was composed of three separate proteolytic bands. Among the three proteolytic bands, the 32 kDa sperminogen band which showed the strongest proteolytic activities upon activation was sliced out and eluted from the gel fragments. The eluted 32 kDa sperminogen was then subjected to peptide sequencing. Since the N-terminus of the 32 kDa sperminogen was blocked for peptide sequencing by Edman degradation method, the internal amino acid sequence of the sperminogen was obtained from the CNBr-digested peptides of sperminogen. The amino acid sequence of the analyzed peptide of the 32 kDa sperminogen showed 100% identity with that of proacrosin.

Identification of hydrolase binding activities of the acrosomal matrix of hamster spermatozoa

The interior of the mammalian sperm acrosome contains a structural framework, the acrosomal matrix, that may regulate both the distribution of hydrolases within the acrosome and their release during the acrosome reaction. To define the biochemical basis of this interaction, we examined the binding of two acrosomal hydrolase, proacrosin and N-acetylglucosaminidase (NAGA), to a purified acrosomal matrix fraction of hamster spermatozoa. Proacrosin-acrosin was chromatographically purified from acid extracts of hamster spermatozoa and consisted of four size variants of 50 kDa, 49 kDa, 45 kDa, and 43 kDa. Each of the four isoforms exhibited the same N-terminal amino acid sequence through 16 residues, suggesting that they may be modified by cleavage at the C-terminus. Polyclonal antiserum against the proacrosin isoforms specifically binds the acrosomal cap as shown by immunofluorescence microscopy. Neither proacrosin nor NAGA were solubilized when sperm were permeabilized with Triton X-100 under low ionic strength conditions; however, both hydrolases were releases by extraction with Triton X-100 containing 0.5 M NaCl. An acrosomal matrix fraction isolated under low ionic strength conditions retained bound proacrosin-acrosin and NAGA, and both hydrolases were released from the matrix by subsequent high-salt extraction. After high-salt treatment, the acrosomal matrix retained specific binding sites for both proacrosin and NAGA. In a blot overlay assay, a set of acrosomal matrix polypeptides between 29 kDa and 24 kDa specifically bound proacrosin. These data suggest that specific interactions between acrosomal matrix polypeptides and hydrolases represent a mechanism to sequester hydrolases within the acrosome and to regulate their release during the acrosome reaction.

Analysis of polysulfate-binding domains in porcine proacrosin, a putative zona adhesion protein from mammalian spermatozoa

Proacrosin is one of the major proteins found within the acrosomal vesicle of mammalian spermatozoa. Previous work has shown that it binds non-enzymatically and with high affinity to polysulfate groups on zona pellucida glycoproteins (ZPGPs) thereby leading to the hypothesis that at fertilization it functions as a secondary ligand molecule to retain acrosome-reacted spermatozoa on the surface of the egg. In the present work we have investigated the nature and extent of the polysulfate binding domain on boar sperm proacrosin using a combination of group-specific modifying reagents, fragmentation analysis, peptide synthesis and expression of deletion recombinants in E. coli bacteria. Taken overall, our results show that arginine, lysine and histidine residues located between Gly 93 and Ala 275, together with the participation of His 47 and Arg 50, are necessary for maximum polysulfate binding activity. The secondary and tertiary structure of this central peptide domain is also important to ensure correct alignment of basic residues with complementary sulfate groups on ZPGPs. Proacrosin, therefore, has many properties in common with other polysulfate binding proteins, such as antithrombin III and sea urchin sperm binding, in having a conformation-dependent domain containing basic amino acids that mediates specific protein-protein interactions. These observations strengthen the hypothesis that proacrosin is a multifunctional protein with a major role as a ligand molecule at fertilization.

Purification, characterization, and N-terminal amino acid sequence of the adenylyl cyclase-activating protease from bovine sperm

We previously reported the extraction of a factor from bovine sperm that activated adenylyl cyclases of rat brain and human platelets, and identified it as a trypsin-like protease that was referred to as "ninhibin." This proteolytic activity was purified to near homogeneity from an alkaline extract of washed sperm particles by sequential chromatography on p-aminobenzamidine agarose and CM-Sephadex. Purification was greater than 100-fold with nearly 30% recovery of protease activity exhibiting a major band of approximately 40 kDa. An approximately 45-kDa form of the protease was also evident in crude extracts and was preferentially isolated when the enzyme was prepared in the presence of a mixture of protease inhibitors. The larger form of the protease was substantially less effective in stimulating adenylyl cyclase than was the smaller form; it is likely to be a zymogen form from which the smaller, more active form is derived. Purified forms of acrosin and ninhibin exhibited similar mobilities on PAGE, similar capacities for activating adenylyl cyclase, similar patterns of proteolytic fragmentation, and similar immunoblot patterns obtained with an antibody against purified bovine acrosin. More importantly, the N-terminal amino acid sequence of bovine ninhibin was found to be identical with that of bovine acrosin and caprine acrosin and more than 75% identical with porcine acrosin. The data support the conclusion that the adenylyl cyclase-activating protease previously referred to as ninhibin is, in fact, acrosin.

The sperm acrosomal matrix contains a novel member of the pentaxin family of calcium-dependent binding proteins

The sperm acrosome is a regulated secretory granule that undergoes exocytosis during fertilization. To elucidate the structural organization of the contents within the acrosome, guinea pig sperm acrosomal apical segments were isolated and mapped by two-dimensional polyacrylamide gel electrophoresis (PAGE). Although complex, the two-dimensional PAGE map was dominated by two M(r) 50,000 polypeptides (p50 and proacrosin), a M(r) 67,000 polypeptide (p67), and a M(r) 32,000 polypeptide (sp32). Proacrosin (pI > 8.0), p67, and sp32 were extracted from apical segments by 1 M NaCl. Protein p50, a relatively acidic polypeptide, was not extracted in 1 M NaCl and/or 1% Triton X-100 at 4 degrees C, but was solubilized with 6 M urea. Protein p50 was purified from the urea extract by elution from DEAE-Sephacel with 100 mM guanidine HCl and appeared homogeneous by SDS-PAGE. Antibodies to p50 were monospecific as judged by Western blot analysis. Indirect immunofluorescence indicated that p50 was restricted to the acrosomal apical segment. Incubation of apical segments at pH 7.5 in the presence of 1 mM EDTA at 37 degrees C resulted in the release of p50 into the 200,000 x g supernatant fluid, a process that was reversed by a subsequent incubation with 1.5 mM CaCl2, but not with MgCl2. The Ca(2+)-dependent reassociation of p50 with the acrosomal apical segments was reversed by the addition of 2.0 mM EGTA, indicating that p50 binding is dependent on free Ca2+ concentrations. When acrosomal matrices were purified following Triton X-100 extraction, p50 was the major component, with p67, proacrosin, and sp32 as less prominent constituents. Molecular cloning demonstrated that p50 is a unique, testis-specific member of the pentaxin family of calcium-dependent binding proteins.

Purification and characterization of a novel acrosin-like enzyme from boar cauda epididymal sperm

A trypsin-like protease was extracted with 1% cetyltrimethylammonium bromide (CTAB) at pH 7.0 from boar cauda epididymal sperm nuclei whose acrosin had previously been removed by acid extraction. The CTAB-extracted sperm protease (CSP) was purified by ion-exchange chromatography on CM-23, gel filtration on Sephadex G-100, affinity chromatography on benzamidine-CH-Sepharose 4B, and HPLC on CM-5PW. CSP is a two chain protein composed of M(r) 2.6K and M(r) 37K chains, which are covalently cross-linked by disulfide bonds. CSP exhibited a pH optimum between pH 8.0 and 9.0, and was inhibited by diisopropyl phosphorofluoridate, antipain, leupeptin, and 1-chloro-3-tosylamide-7-amino-L-2-heptanone. The activity of CSP was enhanced about 1.2-fold with 50 mM CaCl2, with which acrosin is enhanced 2.0-fold. The catalytic efficiency (kcat/Km) of CSP toward Bz-L-Arg-OEt, Tos-L-Arg-OMe, and Tos-L-Lys-OMe in the presence of 50 mM CaCl2 differed from that of acrosin by factors of 0.53, 1.2, and 0.80, respectively. Amino acid sequencing of V8-digested peptides of CSP, and its L- and H-chains showed that the amino acid sequence of CSP was closely related to, but different from, that of acrosin. These results suggest that CSP is a novel acrosin-like enzyme that differs from acrosin in its location in the sperm head, the effect of calcium ions on its activity, and its substrate specificity.

Some effects of zona pellucida glycoproteins and sulfated polymers on the autoactivation of boar sperm proacrosin and activity of beta-acrosin

The effects of zona pellucida glycoproteins, sulfated polymers and non-sulfated polymers on the activation kinetics of boar sperm proacrosin to beta-acrosin have been investigated. The aim has been to understand more about the behaviour and function of this protein after it has been released from the acrosome at the time of fertilization. Purified proacrosin was allowed to autoactivate at pH 8.0 in the presence of different concentrations of homologous zona glycoproteins, sulfated polymers (fucoidan, chondroitin sulfates A, B and C, dextran sulfate, polyvinylsulfate and heparin) and non-sulfated polymers (dextran, polyvinylphosphate and hyaluronic acid). Enzyme activity was measured against N-benzoyl-L-arginine p-nitroanalide substrate and changes in molecular mass of the protein monitored by SDS-PAGE. Results show that zona pellucida glycoproteins, fucoidan, dextran sulfate and polyvinylsulfate all potentiate the conversion of proacrosin to beta-acrosin but subsequently inhibit its amidase activity. Dextran, polyvinylphosphate, chondroitin sulfates A, B and C and glucose-6-sulfate, on the other hand, either have no effect on autoactivation and beta-acrosin activity, or enhance it slightly. SDS-PAGE analysis confirmed these observations and further indicated that binding of sulfated polymers to proacrosin inhibited staining by Coomassie Blue. These results are consistent with the hypothesis that binding of zona pellucida glycoproteins and sulfated compounds to proacrosin/acrosin is stereospecific and that contact activation onto soluble 'surfaces' causes conformational changes that are responsible for potentiation or inhibition of activation. The implications of these findings for sperm binding and penetration of the zona pellucida are discussed.(ABSTRACT TRUNCATED AT 250 WORDS)

Proteolytic enzymes in seminal plasma of domestic turkey (Meleagris gallopavo)

Protease and basic amidase activity was found in the seminal plasma of the domestic turkey. Amidase activity, measured through use of N-alpha-benzoyl-DL-arginine-p-nitroanilide-HCL (BAPNA), was 23-28 times greater for turkey than for guinea fowl or chicken. Within the reproductive tract, seminal plasma from the vas deferens had much greater activity than testicular or epididymal fluids. Turkey seminal plasma enzyme (TSPE) purified by chromatography or isoelectric focusing showed three protein bands by PAGE, each resolving on SDS-PAGE into two subunits with molecular weights of approximately 28,000-32,000 and 38,000-44,000. One of the three proteins also contained a larger subunit (M(r) 76,000-81,000) thought to be transferrin. Turkey acrosin consisted of three subunits with molecular weights below 20,500. Acrosin, but not TSPE, was visualized in native gels with N-alpha-benzoyl-DL-arginine-beta-naphthylamide (BANA)/Fast Garnet stain. Michaelis constants (BAPNA) for TSPE, acrosin, and trypsin were 2.41 +/- 0.12 x 10(-4) M (n = 5), 4.96-6.03 x 10(-4) M (n = 2), and 6.76 +/- 0.95 x 10(-4) M (n = 6), respectively. TSPE, like acrosin and trypsin, was inhibited by benzamidine but not iodoacetamide. While all natural trypsin inhibitors tested inhibited acrosin, TSPE was not inhibited by ovomucoid from chicken or turkey egg white.

Bovine proacrosin from cauda epididymal sperm: purification, characterization and partial sequencing at N-terminus

1. In the present study, we isolated the two forms of proacrosin from acid extracts (pH 3.0) of cauda epididymal bovine spermatozoa by ammonium sulfate fractionation, gel filtration on Sephadex G-150 and affinity chromatography on Concanavalin A Sepharose 4B. The overall purification was 13-fold with respect to crude acid acrosomal extract. 2. The apparent molecular weight of the proacrosins determined by SDS-PAGE were 44,000 and 38,000. Both forms have proteinase activity on gelatin-SDS-polyacrylamide gel electrophoretic zymography. 3. The M(r) = 38,000 component was isolated by reverse phase HPLC. Thirty-nine amino acid residues at the N-terminus have about 72 and 77% sequence similarity with boar and human proacrosin, respectively. 4. The amino acid sequence of 14 amino acids at the N-terminus of the high molecular weight component (M(r) = 44,000) was determined after electroblotting on a polyvinylidene difluoride membrane. This portion of the molecule is identical with that of the low molecular weight component. 5. Proacrosin autoactivation followed the sigmoidal activation curve.

Mechanism of maturation and nature of carbohydrate chains of boar sperm acrosin

The acrosin zymogen proacrosin exists in two molecular forms which are believed to be single-chain polypeptides. During autoactivation in a cell-free system, the 55 and 53 kDa zymogens are sequentially converted into the 49, 36, 31 and 25 kDa forms. A similar mechanism of maturation was revealed, when the calcium ionophore A23187 was added to suspensions of boar spermatozoa. The 49 kDa form has been identified as the first active acrosin form in the maturation cascade. However, this form is indistinguishable from the 53 kDa zymogen in SDS-PAGE at nonreducing conditions. Two carbohydrate chains were evidenced on the acrosin molecule. The chain attached to the Asn3 of the acrosin light chain was enzymatically cleaved without loss of acrosin activity. By contrast, the carbohydrate chain linked to the acrosin heavy chain could be cleaved only after acrosin denaturation. Based on the susceptibility of acrosin to endoglycosidases F and H, a biantennary structure of both carbohydrate chains is proposed.

Activation and subsequent degradation of proacrosin is mediated by zona pellucida glycoproteins, negatively charged polysaccharides, and DNA

Boar proacrosin (E.C. 3.4.21.10, Mw 53 kD) was isolated by a modified method and subjected to autoactivation. Previously described molecular intermediates of 49 and 43 kD and a stable form (beta-acrosin, 35 kD) were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Autoactivation was expedited in the presence of either zona pellucida glycoproteins, fucoidan, or DNA. The end point of this accelerated conversion was the complete degradation of otherwise stable beta-acrosin via the formation of a characteristic active intermediate protein of 30 kD. All intermediate molecular forms observed during proacrosin activation/conversion exhibited the N-terminal sequence of the boar acrosin heavy chain, indicating a C-terminal processing mechanism. Hence zona pellucida glycoproteins stimulate proacrosin activation as well as acrosin degradation. Such a mechanism of proenzyme activation and degradation is to our knowledge described here for the first time and points to a previously unrecognized role of zona pellucida during gamete interaction.

Human acrosin: purification and some properties

Human sperm with normal morphology and good viability were obtained by centrifugation using a discontinuous Percoll density gradient with an inner column. Acrosin (E.C.3.4.21.10) was rapidly purified from sperm by ion exchange adsorption and elution and was purified by affinity adsorption on a lima bean trypsin inhibitor (LBTI) Cellulofine column. The final preparation was found to be homogeneous on polyacrylamide gel electrophoresis and to have a molecular weight of about 4 x 10(4) daltons. The enzyme had an esterolytic activity of 3.5 mumol/min/A280 with N-alpha-tosyl-L-arginine methyl ester as the substrate. Human acrosin showed a broad substrate specificity for arginine and lysine derivatives and it seemed to have a somewhat different specificity from trypsin. The optimal pH of this enzyme with amidolytic activity was 9.0. Enzyme activity was stimulated by a high concentration of calcium chloride. LBTI and aprotinin strongly suppressed the amidolytic activity with the D-valyl-L-leucyl-L-arginine-p-nitroanilide (Val-Leu-Arg-pNA) as the substrate, but alpha 1-antitrypsin and soybean trypsin inhibitor were less effective.

Identification of a proacrosin precursor in the cell-free translation of boar testicular poly(A)(+)-mRNA

A cell-free translation system was used to determine the molecular mass of the protein component of precursor(s) to boar proacrosin. Poly(A)(+)-mRNA was extracted from freshly excised boar testis into phenol/chloroform, precipitated in chilled (-20 degrees C) ethanol, then translated in a cell-free, reticulocyte lysate system with Tran 35S-label. Analysis of the resulting products by SDS-PAGE followed by autoradiography demonstrated multiple bands of translated proteins. Both Western blotting and immunoprecipitation with a specific polyclonal antibody to boar proacrosin yielded a single major band with a relative molecular weight of approximately 64,000. These results suggest that proacrosin (Mr = 53,000-55,000), which contains both protein and carbohydrate moieties, results from the cellular processing of a proacrosin precursor molecule.

Zona pellucida-binding of boar sperm acrosin is associated with the N-terminal peptide of the acrosin B-chain (heavy chain)

Recently, it has been shown that boar acrosin exhibits a carbohydrate-binding activity with a specificity to fucose, by which it can bind to the oocyte zona pellucida. By limited autoproteolysis of a high-molecular mass acrosin (55/53 kDa), designated as alpha-acrosin, a 15 kDa fragment was generated which interacts strongly with the porcine zona pellucida. Zona-binding was demonstrated on protein blots and by the solid-phase zona-binding assay utilizing biotinylated zona proteins. The zona-binding peptide was isolated by reversed-phase HPLC and analyzed for amino acid sequence. Its single N-terminal sequence corresponded to that of the acrosin B-chain (heavy chain). These data indicate that the zona-binding properties of acrosin are associated with the N-terminal peptide of the acrosin heavy chain.

Chicken acrosin: extraction and purification

The objective of the present research was to identify a procedure whereby chicken acrosin could be purified. Acrosin, as evidenced by amidase activity, was extracted with urea most efficiently at a concentration of 6 M. Extraction efficiency was enhanced by spermatozoal lysis prior to admixture with 6 M urea. Lysis was induced by passage of spermatozoal suspensions through a French pressure cell. Acrosin was purified by using gel filtration, chromatofocusing, and affinity chromatography. Based on amidase activity, a 19-fold purification was obtained with a 28% recovery. Native electrophoresis resolved two major protein bands with proteolytic activity. The methods described afford the procurement of milligram amounts of chicken acrosin.

Is sperminogen a modified proacrosin? Isolation, purification, and partial characterization of low-molecular-mass boar proacrosin

Low-molecular-mass zymogen was extracted from boar spermatozoa together with proacrosin using 10% acetic acid supplemented with 10% glycerol, and was purified by the sequential use of gel filtration on Sephadex G-75 and (FPLC) reversed-phase chromatography. LMM zymogen represented approximately 5% of the latent trypsin-like activity present in the sperm extract. SDS-PAGE indicated a molecular mass of 33 kDa. The zymogen reacted with both mouse monoclonal and rabbit polyclonal antibodies to boar acrosin. Determination of the N-terminal sequence of 34 amino-acid residues revealed its identity with the known N-terminal sequence of boar proacrosin.

Mouse preproacrosin: cDNA sequence, primary structure and postmeiotic expression in spermatogenesis

The primary structure of mouse preproacrosin was deduced by nucleotide sequencing of cDNA clones isolated from a mouse testis cDNA library. The largest cDNA, with 1373 bp, consists of a 11-bp 5'untranslated sequence, a 1254-bp open reading frame terminated by a TGA triplet and a 105-bp 3' untranslated end, including one potential polyadenylation signal. The NH2-terminus of the polypeptide contains a hydrophobic 15-amino acid signal peptide. This cleavable signal sequence is followed by 403 amino acids, representing the acrosin light and the heavy chain of 23 and 380 amino acid residues, respectively. The proteolytic active site segments His, Asp and Ser are part of the heavy chain, as well as a proline-rich COOH-terminus, which is not present in any other serine proteinase studied so far. Furthermore the postmeiotic expression of the preproacrosin gene during mouse spermatogenesis was studied.

Regulation of proacrosin conversion in isolated guinea pig sperm acrosomal apical segments

Following sodium dodecyl sulfate-polyacrylamide gel electrophoresis, proacrosin has been identified in extracts of intact guinea spermatozoa as a major silver staining band which reacted immunologically with antibodies made against purified proacrosin from guinea pig testis. Proacrosin exhibited an approximate Mr of 50,000 and was rapidly converted to an Mr 45,000 protein following induction of the acrosome reaction with 2.0 mM CaCl2 and 1 micrograms/ml A23187. Apical segments isolated at pH 6.0 from guinea pig spermatozoa also contained a major silver staining band of Mr 50,000 which cross-reacted with antibodies to guinea pig testis proacrosin. Subcellular fractionation of spermatozoa indicated that proacrosin remained in the particulate fraction of homogenized spermatozoa and was enriched within the isolated acrosomal apical segment. When apical segments isolated at pH 6.0 were incubated at pH 7.5, proacrosin was rapidly converted to the Mr 45,000 form observed in spermatozoa undergoing the acrosome reaction. The conversion process in isolated apical segments was inhibited by leupeptin and was accelerated in the presence of calcium, magnesium, and manganese. Zinc completely inhibited the conversion of proacrosin to the Mr 45,000 protein. Neither proacrosin nor the Mr 45,000 protein were released into the supernatant fluid during the incubation of apical segments at pH 7.5. Furthermore, the proteins were resistant to solubilization by 150 mM NaCl and 1% Triton X-100 but were solubilized by treatment of apical segments with 1 M NaCl. These results provide evidence as to the identity and subcellular distribution of proacrosin in intact guinea pig sperm prior to zymogen conversion and suggest that isolated apical segments exhibit a subset of the exocytotic reactions leading to completion of the acrosome reaction.

Isolation of the boar sperm acrosin peptide released during the conversion of alpha-form into beta-form

The sperm proteinase acrosin occurs in several enzymatically active forms which differ from each other in molecular mass. The high-molecular-mass alpha-form (53 kDa) is converted into the low-molecular-mass beta-form (38 kDa) by auto-proteolysis. As these two forms possess identical N-termini and identical A-chains (light chains) the difference must reside in the C-terminal parts of their B-chains (heavy chains). It could be demonstrated by gel electrophoresis that on incubation of alpha-acrosin, in addition to beta-acrosin, a main degradation product of approx. 18 kDa was formed. This fragment was isolated by gel filtration chromatography. The amino-acid composition of the fragment corresponded to the difference between that of alpha-acrosin and of beta-acrosin, and showed a strikingly high proportion of proline. It is suggested that this hydrophobic segment from the C-terminal region of alpha-acrosin accounts for the special membrane-associating property of the enzyme.

Caprine acrosin. Purification, characterization and proteolysis of the porcine zona pellucida

Acrosin purified from an acidic extract of ejaculated goat spermatozoa migrated as a single 42,000-Mr band in SDS/polyacrylamide-gel electrophoresis. Reduction and alkylation of caprine acrosin produced two polypeptides, one of Mr 40,000 (heavy chain) and the other of Mr 3700 (light chain). The light chain purified by reversed-phase h.p.l.c. was a glycosylated octadecapeptide with an amino acid sequence similar to that of the N-terminal 18 residues of porcine acrosin light chain (78% positional identity). The sequence of the N-terminal 37 amino acids of purified caprine acrosin heavy chain is similar to that of porcine acrosin heavy chain (70% positional identity through 37 residues). Studies with synthetic substrates and synthetic and natural proteinase inhibitors confirmed both the specificity of the purified proteinase for Arg-Xaa and Lys-Xaa bonds and a serine-proteinase mechanism. Purified caprine acrosin hydrolysed the 90 kDa and 65 kDa components, but did not hydrolyse the 55 kDa component of the porcine zona pellucida. The action of the enzyme on the porcine zona pellucida was indistinguishable from that previously reported for porcine acrosin.

Boar proacrosin is a single-chain molecule which has the N-terminus of the acrosin A-chain (light chain)

Boar proacrosin was isolated from spermatozoa by a novel procedure under conditions preventing proenzyme activation. The spermatozoal extract was fractionated by gel filtration and reversed-phase FPLC, all in acidic solutions. Isolated proacrosin had a molecular mass of 55/53 kDa (doublet) and was devoid of amidolytic activity. Its single N-terminal sequence corresponded to that of the 23-residue acrosin A-chain and continued with that of the acrosin B-chain. Autoactivation at pH 7.8 did not influence the molecular mass. However, activated material contained two parallel N-terminal sequences, those of the A- and B-chain. Thus, activation of proacrosin is analogous to that of other serine proteinase proenzymes.

Turkey acrosin. I. Isolation, purification, and partial characterization

Acrosin was extracted from turkey spermatozoa by use of urea together with sonication and freezing, and purified approximately 18-fold by sequential use of chromatofocusing and affinity chromatography. The use of chromatofocusing for the initial purification step proved to be superior to preparative isoelectric focusing. Similar to acrosin from many mammalian species, turkey acrosin was found to be a glycoprotein possessing characteristics of serine proteases. Polyacrylamide gel electrophoresis (PAGE) of the enzyme indicated the presence of two isozymes. Sodium-dodecyl sulfate PAGE under reducing conditions revealed three subunits with approximate molecular weights of 11,700, 13,900, and 15,900.

Radiation inactivation of hamster acrosin reveals that the biologically active unit is of low molecular size

The relationship between structure and activity of acid-extracted and purified acrosin obtained from cauda epididymal hamster spermatozoa was studied. A four-step purification procedure of acrosin was used; it included 1.) acid extraction, 2.) gel filtration over Sephadex G-100 resin, 3.) ion exchange on CM-Sepharose CL-6B, and 4.) affinity chromatography on proflavin-Sepharose 4B. Analysis of the purified enzyme by high-performance liquid chromatography (300 SW + I-125) revealed a molecular weight of 44,000, which was identical to that obtained for acid-extracted acrosin. Slab-gel electrophoresis under nondenaturing conditions showed only one active band, as revealed with a highly sensitive assay using N alpha-benzyloxycarbonyl-L-lysine thiobenzyl ester as substrate. The radiation inactivation size of acid extracted acrosin was calculated to be 8400. This small unit could represent the active polypeptide portion of a larger monomer molecule or could represent the size of active subunits. Because acrosin is autocatalytic and highly active during fertilization, it is suggested that the active portion of the completely processed form of the enzyme is of small molecular weight.

Purification and initial characterization of guinea pig testicular acrosin

Guinea pig (GP) acrosin was purified following acid extraction of testicular acetone powder, pH precipitation of the soluble extract, gel filtration on Sephadex G-100, ion-exchange chromatography on SP-Sephadex, and affinity chromatography on Concanavalin A-Sepharose. Final purification was achieved by re-chromatography on Sephadex G-100. Enzymatic activity was detected by following the hydrolysis of N-benzyloxycarbonylarginyl amide of 7-amino-4-trifluoromethylcoumarin at 37 degrees C, pH 8.0, before and after activation. GP testicular acrosin exhibited a molecular weight of 48,000 by gel filtration and 34,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Following SDS-PAGE in gels containing 0.1% gelatin, protease activity was observed to comigrate with the major protein detected by silver staining. The purified GP acrosin showed cross-reactivity with a monospecific polyclonal rabbit antiserum directed against boar sperm acrosin and exhibited reversible pH-dependent activation. The physiochemical characteristics of the purified protein, including the amino acid composition, resemble those reported for acrosins from other species.

Purification and initial characterization of proacrosins from guinea pig testes and epididymal spermatozoa

Previous studies showed that interspecies differences in proacrosin size may exist. We purified guinea pig proacrosins, one from testes and two from epididymal spermatozoa, by gel filtration and cation exchange at acidic pH. Final purification was by cation exchange at pH 8.0 in 6 M urea. Testis proacrosin migrated with 62,000 Mr in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). One sperm proacrosin migrated with 43,000 Mr, and the other as a 56,000/54,000 Mr doublet in SDS-PAGE. These results represent the first purification of three forms of proacrosin from one species, and the first purification to homogeneity of a 43,000 Mr proacrosin. The proacrosins autoactivate at pH 8.0 with similar kinetics, copurify until the last purification step, and share antigenic determinants. It is possible that the sperm proacrosins are derived from the testis proacrosin, perhaps by proteolysis. The sizes of the three guinea pig proacrosins reported in this study are similar to those reported for proacrosins from other species. Apparent interspecies differences in proacrosin size may be primarily a question of which of at least three possible forms of the zymogen predominates in a species.

Evolution and development of the outer acrosomal membrane (OAM) and evidence that acrosin-inhibitors are proteins of the OAM

An antiserum to the purified porcine outer acrosomal membrane (OAM) was raised in rabbits and the IgG fraction isolated by ammonium sulphate precipitation and ion exchange chromatography. The antibodies reacted exclusively with the acrosomal cap of the sperm head as revealed by indirect immunofluorescence. In addition they cross-reacted not only with the acrosomal part of the spermatozoa of all mammalian species tested (bull, horse, rabbit, rat, mouse, hamster, mole, antelope, monkey, man) but also with the spermatozoa of the cock (Class: birds) and the rainbow trout (Class: fish). All the species exhibited similar development of the acrosomal cap during spermatogenesis, with the appearance of the immunofluorescent stain in early round spermatids. In the mole the localization of the acrosome in elongated testicular spermatids differed from that in all other species: Instead of prominent fluorescence over the apical part of the sperm an equatorial belt was formed. The cross-reactivity of the anti-boar OAM antibody with the acrosomes of different vertebrate species at the morphological level was supported by the results of Western blotting experiments with purified boar OAM proteins and the SDS-extractable proteins of bull and human spermatozoa, respectively. Using anti-OAM antibodies and antibodies against the acrosin inhibitors I and II described recently by Tschesche et al. (1982), in absorption and Western blotting experiments, it was demonstrated that the acrosin inhibitor proteins are integrated in the outer acrosomal membrane.

Two satisfactory methods for purification of human acrosin

Acrosin has been purified from human sperm cells by two alternative procedures which give purer products and in higher yields than could be achieved previously. The products were characterized by their molecular weight, catalytic action, sensitivity to inhibitors, and reaction with a polyclonal anti-acrosin antibody. After acid extraction of the cells, one method involves removal of acrosin inhibitors by vacuum dialysis, followed by affinity chromatography on a soybean trypsin inhibitor (SBTI) column, and therefore requires that the acrosin be in an active form capable of binding to the inhibitor. The other method involves affinity chromatography on a column of a monoclonal anti-acrosin antibody (MAb) and can be used to provide either active or proenzyme forms of acrosin, by choice of extraction conditions and inclusion of appropriate inhibitors. The yield of human acrosin from the SBTI method was 104% and from the MAb column was 75%. It is hoped that these procedures will make the very scarce human acrosin more readily available for further study.

The rapid purification and partial characterization of human sperm proacrosin using an automated fast protein liquid chromatography (FPLC) system

A rapid and efficient procedure was developed for obtaining highly purified human proacrosin. Ejaculated spermatozoa were washed via centrifugation through 1 M sucrose containing 50 mM benzamidine and acid-extracted in the presence of benzamidine. The solubilized material was dialyzed then lyophilized. The sample was resuspended in 8 M guanidine hydrochloride in acetic acid (0.5 M) pH 2.5 and then subjected to gel permeation chromatography with an automated fast protein liquid chromatography system utilizing two Pharmacia Superose 12 columns set in tandem that were equilibrated in the same buffer. The proacrosin eluted as an individual peak that was well separated from another proteinase zymogen referred to as sperminogen. The proacrosin preparation was determined to be highly purified when observed on silver-stained SDS-polyacrylamide gels as well as on gelatin-SDS-polyacrylamide gels. The proacrosin appeared as a doublet (Mr = 55,000 and 53,000) on both of these systems. The autoconversion of proacrosin to acrosin at pH 8 resulted in a typical sigmoidal autoactivation curve. Following protein staining of SDS-polyacrylamide gels, it was shown that upon activation of purified proacrosin preparations the 55,000 and 53,000 molecular weight proteins were initially degraded to a 49,000 form and then to several lower molecular weight forms (Mr = 40,000-34,000). Similar findings with regard to proteolytic digestion were observed following gelatin-SDS-polyacrylamide zymography except that an increase with time in proteinase intensity between 58,000 and 53,000 was also observed. Cobalt and calcium were found to be potent inhibitors of the conversion of proacrosin into acrosin, while sodium resulted in much less inhibition of this process. Calcium was found to markedly enhance the proteolytic activity of human acrosin, while it had no observable influence on the acrosin hydrolysis of benzoylarginine ethyl ester. Thus, the described purification procedure resulted in a highly purified proacrosin preparation in sufficient yields to allow for its partial characterization.

Expression of acrosin during mouse spermatogenesis: a biochemical and immunocytochemical analysis by a monoclonal antibody C 11 H

A monoclonal antibody C 11 H was produced against human acrosomal antigen. It also cross-reacted with acrosomes of the boar and the mouse. In boar spermatozoa the antibody reacted, in immunoblotting analysis, with polypeptides of Mr 55,000 and 53,000. The proteolytic activity was detected by zymographic casein overlay assay. Partially purified boar sperm acrosin was bound by the C 11 H affinity column, and acrosin activity was detected in the eluate. These experiments indicate that C 11 H antibody recognizes sperm acrosin. The acrosin expression during spermatogenesis was studied with C 11 H antibody, using mouse testis as a model. Immunocytochemical analysis revealed that step 9 spermatids were the first cells to react with C 11 H antibody. During step 14, the perinuclear pattern of C 11 H-binding disintegrated into small particles around the spermatid nuclei for the period of close association between spermatid bundles and Sertoli cells. During late step 15, the antigen became located at the site in the acrosome typical for step 16 spermatids and spermatozoa. These results indicate that monoclonal C 11 H antibody recognizes acrosin that is first expressed in haploid cells coincident with the onset of nuclear elongation and cessation of RNA transcription. The changes in the distribution pattern suggest that acrosin may be modified by Sertoli cells. In addition to studies on acrosin, this antibody may be useful in investigations of transcription and translation and their regulation during spermatogenesis in general.

Comparative activation studies with extracted and purified human proacrosin

Proacrosin was purified from acid extracts of human spermatozoa by concanavalin A precipitation and Bio-Gel P-100 chromatography. Two molecular weight forms of proacrosin were obtained, a major one with a Mr of 70,000-71,000 and a minor one with a Mr of 47,000-53,000. In contrast to sperm extracts, the purified forms of proacrosin were free of acrosin inhibitor(s) and nonzymogen acrosin. By modulating pH, ionic strength and temperature, the activation of proacrosin in sperm extracts was compared to only the major form of purified proacrosin, since it seemed to be the source of the lower molecular weight form of proacrosin. In both preparations, proacrosin activation occurred maximally over a broad pH range (7.6-8.8 for purified proacrosin and 7.6-9.6 for extract). Additionally, an ionic strength of 0.1 and above caused a decrease in proacrosin activation in both preparations. Similarly, proacrosin was sensitive to short incubation periods at 45 degrees C and above which caused a decrease in the amount of proacrosin found in both preparations.

Ram proacrosin. A simple method for isolation of proacrosin free of inhibitors, and proacrosin autoactivation studies

Two partially purified proacrosin forms have been obtained from acid extracts of ram ejaculated spermatozoa by Sephadex G-100 column chromatography in 0.001 M HCl. The form obtained from the extracts of whole ejaculates with apparently higher molecular mass was free of any acrosin inhibitor and was used for autoactivation studies. The autoactivation followed a classical S-shaped activation curve and was a two-step process. The presence of calcium ions slowed down the autoactivation process and stabilized the active acrosin formed. The activity of latter rapidly decreased when the pH of the fully activated mixture was adjusted to pH 3. The activity was not restored by re-adjusting the pH to 8. A proacrosin with apparently lower molecular mass was isolated from the extract of washed spermatozoa. Both proacrosins, however, showed the same molecular mass Mr approximately 58 000 daltons, when examined by gel filtration in 0.1 M NaCl (pH 3).

The amino terminal sequences of boar sperm proacrosin and active acrosin are identical

The amino-terminal amino acid sequence of boar sperm proacrosin was determined. The first 13 amino acid residues in the amino terminal sequence show an exact homology with the amino terminal sequence of boar sperm acrosin.

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.

Purification and characterization of two types of trypsin-like enzymes from sperm of the ascidian (Prochordata) Halocynthia roretzi. Evidence for the presence of spermosin, a novel acrosin-like enzyme

Two types of trypsin-like proteases, spermosin and acrosin, have been highly purified from spermatozoa of the ascidian (Prochordata) Halocynthia roretzi by a procedure including diethylaminoethylcellulose chromatography, Sephadex G-100 gel filtration, and soybean trypsin inhibitor-immobilized Sepharose 4B chromatography. Each purified preparation was judged to be homogeneous on the basis of chromatographic analysis and sodium dodecyl sulfate-gel electrophoresis. The molecular weights of spermosin and acrosin were estimated to be 27,000 and 32,000-34,000, respectively, by gel electrophoresis in sodium dodecyl sulfate. The isoelectric point of the former was 6.5, while that of the latter was 5.5. Non-ionic detergents, e.g. Brij 35, showed marked stabilizing effects on the purified enzymes. Both of these enzymes had pH optima between 8.5 and 9.0, and their activities were enhanced by the addition of calcium chloride. The enzymes were inhibited by diisopropyl fluorophosphate, phenylmethanesulfonyl fluoride, leupeptin, antipain, soybean trypsin inhibitor, aprotinin, ovomucoid, valyl-prolyl-arginyl-chloromethane, glycyl-valyl-arginyl-chloromethane, p-aminobenzamidine, benzamidine, zinc chloride, and mercuric chloride. Lima bean trypsin inhibitor and tosyl-lysyl-chloromethane strongly inhibited acrosin, but not spermosin. While the substrate specificity of acrosin was rather broad, that of spermosin was very narrow; the latter enzyme hydrolyzed only t-butyloxycarbonyl-valyl-prolyl-arginine 4-methylcoumaryl-7-amide among 12 peptidyl-arginine (or lysine) 4-methylcoumaryl-7-amides tested. Thus, the ascidian spermatozoa possess at least two proteases, acrosin and spermosin; the former shows the properties closely related to those of mammalian acrosin (EC 3.4.21.10), but the latter is a unique type of acrosin-like enzyme in respect to the substrate specificity and inhibitor susceptibility.

Purification of mouse sperm acrosin, its activation from proacrosin and effect on homologous egg investments

When proacrosin from mouse epididymal spermatozoa was activated a single form of acrosin was produced. The enzyme was isolated by gel filtration followed by affinity chromatography using Sepharose-4B linked to an acrosin inhibitor p-(p'-aminophenoxypropoxy)benzamidine. The molecular weight of partly purified acrosin was 53 000 by gel filtration, and of the pure enzyme 39 000 by SDS-polyacrylamide gel electrophoresis. Pure mouse acrosin removed the cumulus oophorus, corona radiata and zona pellucida from the homologous egg. It is proposed that penetration of spermatozoa through egg investments, particularly through the zona pellucida, is a simpler process in the mouse than in the sheep.

Acrosin: immunochemical demonstration of multiple forms generated from bovine and human proacrosin

A rabbit antiserum was prepared against purified bovine spermatozoal acrosin (EC 3.4.21.10), and the specific immunoglobulin G (IgG) was isolated by immunoaffinity chromatography. This IgG was shown to be monospecific for acrosin by rocket immunoelectrophoresis and by Western blotting of sodium dodecyl sulfate - polyacrylamide gels onto nitrocellulose sheets, followed by indirect immunodetection. In extracts of bovine spermatozoa prepared in the presence of 50 mM benzamidine, a single form of acrosin was detected, having a relative mass (Mr) of 48 000, which is presumed to be proacrosin. At least four further intermediate forms of acrosin were detectable in extracts prepared in the absence of benzamidine and in the various column eluates, having Mr values of 47 000, 44 000, 42 000, and 40 000, while the final product of the purification had a Mr of 37 500. The rabbit antibovine acrosin antiserum reacted also with human acrosin on Western blots. In this way, human proacrosin was found to have a Mr of 50 000 and to be convertible into intermediate forms of Mr 48 500, 44 500, 40 500, and 37 500, while the final product had a Mr of 35 500.

Boar acrosin. Isolation of two active forms from boar ejaculated sperm

A simple method avoiding the use of nonionogenic detergent has been developed for the isolation of two forms of boar acrosin from ejaculated sperm. Each of the two forms was electrophoretically homogeneous and showed one N-terminal sequence only; Val-Val. The two acrosin forms isolated differ in molecular mass and amino acid composition. alpha-Acrosin, the form showing a higher molecular mass (Mr approximately 50 000), is stable in acid media. When exposed to pH above 4 it is converted into beta-acrosin (Mr approximately 35 000) by autodigestion. The isolation of the alpha-form was therefore carried out below pH 4 to eliminate autodigestion to the beta-form. The beta-form is stable for a certain period at neutral pH, especially if stabilized by Ca2+ ions. The autodigestion of alpha-acrosin to beta-acrosin probably results in the liberation of the C-terminal portion of the molecule of the alpha-form; this portion is composed of roughly 85 residues and is rich in proline.

Acid extraction of acrosin from human spermatozoa pretreated by different physicochemical methods

Washed human spermatozoa were subjected to different physicochemical methods, followed by acid extraction of the sperm acrosomes to dissolve acrosin. The acrosin activity of the sperm pellet and the supernatant was determined by benzoyl arginine ethyl ester/alcohol dehydrogenase (BAEE/ADH) assay to calculate the total acrosin activity in mU/10(6) spermatozoa. Membrane-active and zymogen-activating agents increased the total acrosin activity 50%-200% compared to acid extraction alone. Similar results were obtained by osmotic shock, sonication and treatment with glass beads. Snap freezing of unprotected spermatozoa in liquid nitrogen yielded a fivefold increase in total acrosin activity, thus demonstrating that this is the method of choice for optimal acrosin extraction. The possibility is discussed as to whether acrosomal membrane alterations with improved solubilization of membrane-bound acrosin and/or conformational changes and/or zymogen activation are responsible for the considerable increase observed in acrosin activity.

Purification of bovine and human acrosin

Acrosin from human spermatozoa was required for studies of immunological interference with fertilization, but not detailed purification scheme was available for the human enzyme. Since human semen samples cannot be obtained cheaply or in large numbers and contain relatively small amounts of acrosin, development of purification procedures was carried out with bovine semen. Bovine acrosin had not previously been fully purified, and over 1 mg of pure acrosin was obtained from 100 mL of bovine semen, by a process of saline and Triton X-100 washes of the spermatozoa, 1 mM HCl extraction, gel filtration, and ion-exchange and affinity chromatography. The bovine acrosin had a molecular weight (MW) of 39 000 and a specific activity of 93 U/mg, measured with 0.5 mM benzoyl arginine ethyl ester. The same extraction procedure could be followed for human acrosin, but better yields were obtained in the purification if the ion-exchange step was omitted. The human acrosin had a MW of 49 000, and traces of a 38 000 MW component were sometimes observed. From 14 human semen samples, containing initially 7-10 U of acrosin activity, about 2.5 U (approximately 20 micrograms of protein) could be obtained in a pure state.

Characterization of a high-molecular-weight form of human acrosin. Comparison with human pancreatic trypsin

A high-molecular-weight form of acrosin (alpha-acrosin, EC 3.4.21.10) was extracted from spermatozoa obtained from frozen semen and purified over 300-fold. Purification was effected by sequential use of Sephadex G-150, CM-cellulose and DEAE-cellulose chromatography. Properties of human acrosin were compared with those of human pancreatic trypsin. The molecular weight (Mr) of acrosin (70000) was greater than that of trypsin (Mr 21000). Isoelectric points for acrosin (pI = 9.0) and trypsin (pI = 8.2) were also different. alpha-N-Benzoyl-L-arginine ethyl ester was hydrolysed 50% more rapidly by acrosin than by trypsin. Acrosin had similar kcat. values for the hydrolysis of esters with different acylating groups (i.e. benzoyl-L-arginine and p-tosyl-L-arginine esters). In contrast, trypsin had dissimilar kcat. values for the hydrolysis of esters with different acylating groups. Kinetic data argue against deacylation as the rate-limiting step in ester hydrolysis by acrosin. Acrosin was less sensitive than trypsin to inhibition by 7-amino-1-chloro-3-L-tosylamidoheptan-2-one ('TLCK'), di-isopropyl fluorophosphate and soya-bean trypsin inhibitor. D-Fructose and D-arabinose inhibited acrosin, but had no effect on trypsin. The data indicate that definite differences exist between human acrosin and trypsin.

Studies on acrosin. I. Purification and characterization of boar acrosin

Acrosin was extracted from boar sperm and purified by Sephadex gel filtration and affinity chromatography on Phe-Phe-Arg Sepharose 4B in acidic condition. Its enzymic properties were characterized in comparison with trypsin. The oligopeptides with Arg at the carboxy-termini were used as the ligands for affinity chromatography. Phe-Phe-Arg adsorbed acrosin at pH 5 and released in at pH 3. To adsorb acrosin, it was found that the ligand should be longer than tripeptide with Arg in the carboxy-termini. Disc gel electrophoretogram of purified boar acrosin gave a broad band consisted from three fractions which hydrolysed N-alpha-benzoyl-arginine ethylester (BAEE). The pH optimum and inhibition spectra were similar to those of trypsin, however, the influence of urea on them were very different among each other. Calcium ion decreased Km for BAEE, and increased Ki of aprotinin. The kinetic analysis of acrosin for its substrate and products resulted that Km for BAEE was minimal at around pH 8 and maximal at pH 5, on the contrary, Ki of the product was low at pH 5, but progressively increased along the elevation of pH. The same tendency was observed for trypsin. From the attitudes on the affinity chromatographies and the pH profiles of kinetics parameters, it was concluded that the active sites of acrosin and trypsin were similar to each other.

Purification and properties of boar acrosin

An isolation procedure in the presence of non-ionic detergents has been developed for the large-scale preparation of boar acrosin. Five steps including hydrophobic interaction chromatography on phenyl-Sepharose resulted in a 161-fold purification of the enzyme with an accumulation yield of 41%. The resultant acrosin preparation had a molecular weight of 38,000, an isoelectric point of 10.5 and a specific activity of 37 U/mg. Apparent homogeneity was judged by sodium dodecyl sulfate electrophoresis and isoelectric focusing. A polarity index of 41.2% was calculated from the amino acid composition. Acrosin was stable at pH 5.5 in the presence of 0.1% Triton X-100. In the absence of detergent acrosin was strongly adsorbed on plastic surfaces.

Interactions of boar acrosin with detergents

The activity of boar acrosin was found to be stimulated up to 260% by non-ionic detergents if present in concentrations above their critical micelle concentration. In addition, the stability of acrosin was remarkably enhanced in the presence of 0.1% (w/v) detergents. Triton X-100 was found to reduce the affinity of acrosin to the synthetic inhibitor 6-amidino-2(4'-methoxyphenyl)indole by the factor 2.9 when Ki values were measured in buffer solutions in the presence (0.1%, w/v) and absence of Triton X-100. Phospholipids did nearly completely abolish the acrosin activity, this effect being reversibly by addition of 0.1% (w/v) Triton X-100. These results are interpreted in terms of hydrophobic binding sites exposed on the surface of the acrosin molecule. Hence, for the first time data are presented characterizing acrosin as a membrane-associated protein.

Multiple forms of boar, bull, and human acrosin

Analytical disk gel electrophoresis with staining techniques for amidohydrolase activity at pH 7.6 demonstrated that partially purified acrosomal extracts of ejaculated bull, boar, and human spermatozoa contained three, apparently four, and two fractions, respectively, with acrosin-like activity. Acrosin amidohydrolase activity is present in the gels incubated in the staining medium at pH 5.0. Some methods for the extraction of human acrosin have been compared. These consist essentially of the extraction by detergent treatment and the extraction by acid procedures. Acid extraction of human spermatozoa yields a higher amount of acrosin than does detergent extraction; the acrosin specific activity, extracted by these methods, seems to be similar.

Purification of an acrosin-like enzyme from sea urchin sperm

Sea urchin sperm contain an acrosin-like enzyme with an apparent molecular weight of 53,000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals two subunits of 34,000 daltons and 18,000 daltons. The Mr = 34,000 subunit is the catalytic entity as revealed both by labeling with [14C]diisopropyl phosphorofluoridate and by proteolytic activity after dissociation of the subunits at pH 2.5. Both the 34,000-dalton and the 53,000-dalton forms of the enzyme catalyze the hydrolysis of N alpha-benzoyl-L-arginine ethyl ester and both are inactivated by inhibitors of low molecular weight, whereas only the Mr = 34,000 form is inactivated by large proteinaceous inhibitors. Only the Mr = 34,000 form catalyzes proteolysis of denatured lysozyme or the B chain of insulin. The Mr = 18,000 subunit appears to suppress the proteolytic activity but not the activity toward the small ester substrate. These findings are discussed in terms of possible roles of this enzyme in the control of early events leading to fertilization.