Effect of process parameters on vitamins and sensory acceptability in micronutrient-fortified soymilk prepared by small-scale batch processing

Effects of holding time before cooling, cooling method, and light or dark refrigerated storage on the stability of vitamin A, vitamin C, thiamine, riboflavin, and folate were investigated in fortified and unfortified soymilk. Vitamin C loss (6%) and mild vitamin A isomerization occurred when soymilk was held hot after fortification. Cooling bottled soymilk at ambient temperature or in an ice-water bath did not affect any vitamins. Loss of riboflavin (18%) and vitamin A isomerization occurred during 12 days of light-exposed refrigerated storage, in contrast to no vitamin degradation during dark refrigerated storage. A sensory panel of youth and children indicated no significant preferences between fortified and unfortified soymilk except for color, where the lighter-colored unfortified soymilk was preferred. Acceptable vitamin stability and sensory characteristics can be achieved in fortified soymilk produced in small-scale batch processes with appropriate management of production and storage conditions.

New insights into thyroglobulin pathophysiology revealed by the study of a family with congenital goiter

CONTEXT

Thyroglobulin (TG) gene mutations cause congenital hypothyroidism (CH) with goiter. A founder effect has been proposed for some frequent mutations. Mutated proteins have a defect in intracellular transport causing intracellular retention with ultrastructural changes that resemble an endoplasmic reticulum storage disease.

OBJECTIVE

To reveal new aspects of thyroglobulin pathophysiology through clinical, cellular, molecular, and genetic studies in a family presenting with CH due to TG mutations from Galicia, an iodine-deficient area of Spain.

DESIGN

The included clinical evaluation of family members, DNA sequencing for TG gene mutation and haplotyping analysis, ultrastructural analysis of thyroid tissue specimens from affected subjects, analysis of effects of mutations found on TG gene transcription, and in vitro studies of cellular production and secretion of mutated proteins.

SETTING

Locations included primary care and university hospitals.

RESULTS

Family members with CH, mental retardation, and goiter were compound heterozygous for c.886C-->T (p.R277X) and g.IVS35+1delG. For c.886C-->T, a founder effect cannot be excluded, and its transcription was hardly detectable. g.IVS35+1delG caused an in-frame deletion in exon 35 and produced a protein that, although synthesized, could not be secreted. Ultrastructural analyses showed morphological changes consistent with an endoplasmic reticulum storage disease.

CONCLUSION

The shorter thyroglobulin resulting from the novel g.IVS35+1delG was retained within the endoplasmic reticulum of thyrocytes, and together with p.R227X caused severe hypothyroidism with goiter. p.R277X, the most commonly described TG mutation, is caused by a TG exon-7 highly mutation-prone region, and the possibility that some cases were introduced to South America from Galicia cannot be excluded.

Canine ovariohysterectomy and orchiectomy increases the prevalence of ACL injury

To determine whether canine ovariohysterectomy or orchiectomy affects the prevalence of anterior cruciate ligament injury, we compared injury rates of anterior cruciate ligaments of animals that had gonadectomy and animals that were sexually intact as a function of gender, breed, or size. Records of 3218 dogs treated in one orthopaedic veterinary practice during a 2-year period were retrospectively reviewed. Anterior cruciate ligament injury, diagnosed by a history of acute hind limb lameness and by positive anterior drawer test, was confirmed at the time of surgery. The prevalence of anterior cruciate ligament rupture in all dogs was 3.48%. Females that had ovariohysterectomy and males that had orchiectomy had a significantly higher prevalence of anterior cruciate ligament rupture than the sexually intact dogs. Larger dogs had an increased prevalence of anterior cruciate ligament injury compared with smaller or medium-sized dogs, with the increased rupture rates for sterilized animals holding across breeds and sizes. Sterilization of either gender increased the prevalence of anterior cruciate ligament injury, suggesting a potential effect of gonadal gender on prevalence of injury of this ligament.

Heterogeneous processing and zona pellucida binding activity of pig zonadhesin

Zonadhesin is a mosaic protein in sperm membrane fractions that binds directly and in a species-specific manner to the extracellular matrix (zona pellucida) of the oocyte. The active form of pig zonadhesin from capacitated, epididymal spermatozoa comprises two covalently associated polypeptide chains of M(r) 105,000 (p105) and M(r) 45,000 (p45). Here we report detection and characterization of multiple zonadhesin isoforms in freshly ejaculated cells. Antibodies to the predicted von Willebrand D0-D1, D1, and D3 domains of pig zonadhesin recognized p105, p45, and additional M(r) 60,000-90,000 polypeptides in particulate fractions of uncapacitated cells. Although the p105/45 form constituted a minority of all zonadhesin forms in sperm membrane fractions, it was the predominant form capable of binding to the pig zona pellucida. Zonadhesin-binding sites were distributed over the entire zona pellucida. Anion exchange chromatography resolved active, p105/45 zonadhesin from the p60-90 inactive forms. Without disulfide bond reduction some zonadhesin was M(r) > or = 300,000, including M(r) 300,000 and 900,000 proteins comprising in part multimers of p105/45. The multimeric forms did not bind the zona pellucida as avidly as did the p105/45 monomer. Expressed D1 and D3 domain fragments containing the CG(L/V)CG sequence motif spontaneously formed multimers at -246 mV E(h) in vitro. Double Cys --> Ser mutants of the D1 fragment formed multimers with the same apparent kinetics as the wild type protein. Zonadhesin localized to the apical head of pig spermatozoa. We conclude that a heterogeneous combination of specific proteolysis and intermolecular disulfide bond formation in the sperm head generates multiple forms of zonadhesin with differing avidities for the zona pellucida.

Sex hormones and knee ligament injuries in female athletes

Female athletes tear their anterior cruciate ligaments (ACLs) more frequently than male athletes participating in similar athletic events do. The reasons for this discrepancy are not known. Many possible causative factors, such as size, strength, anatomic, social, and hormonal differences, have been suggested. The possible involvement of normal tissue remodeling events in susceptibility to ACL injury has not been thoroughly examined. We are characterizing gender differences in matrix metalloproteinases and their inhibitors. Results of these studies are summarized and discussed in the context of tissue remodeling in general, with an emphasis on the cell biology of ACL repair.

Expression of matrix metalloprotease and tissue inhibitor of metalloprotease genes in human anterior cruciate ligament

Women are more susceptible to anterior cruciate ligament (ACL) injuries than men performing similar athletic activities. Because tissue remodeling may affect ligament strength, we assessed expression of tissue remodeling effector genes in the human ACL. Specifically, we surveyed ACL for RNAs encoding all known matrix metalloproteases (MMPs) and tissue inhibitors of metalloproteases (TIMPs) by reverse transcription/polymerase chain reaction (RT-PCR). These experiments revealed that mRNAs encoding nine of sixteen MMPs and all four TIMPs are present in the normal ACL. The nine expressed proteases were MMPs 1-3, 7, 9, 11, 14, and 17 (collagenase 1, gelatinase A, stromelysin 1, matrilysin, gelatinase B, stromelysin 3, and membrane types 1 and 4, respectively), and MMP-18. Genes for MMPs 8, 10, 12, 13, 15, and 16 appeared not to be expressed in ACL, as their mRNAs were not detected using RT-PCR conditions that did yield positive signals from other tissues (testis or bone). We conclude that numerous genes encoding tissue remodeling effector proteins are expressedin the human ACL.

Comparative analysis of the gene-dense ACHE/TFR2 region on human chromosome 7q22 with the orthologous region on mouse chromosome 5

Chromosome 7q22 has been the focus of many cytogenetic and molecular studies aimed at delineating regions commonly deleted in myeloid leukemias and myelodysplastic syndromes. We have compared a gene-dense, GC-rich sub-region of 7q22 with the orthologous region on mouse chromosome 5. A physical map of 640 kb of genomic DNA from mouse chromosome 5 was derived from a series of overlapping bacterial artificial chromosomes. A 296 kb segment from the physical map, spanning ACHE: to Tfr2, was compared with 267 kb of human sequence. We identified a conserved linkage of 12 genes including an open reading frame flanked by ACHE: and Asr2, a novel cation-chloride cotransporter interacting protein Cip1, Ephb4, Zan and Perq1. While some of these genes have been previously described, in each case we present new data derived from our comparative sequence analysis. Adjacent unfinished sequence data from the mouse contains an orthologous block of 10 additional genes including three novel cDNA sequences that we subsequently mapped to human 7q22. Methods for displaying comparative genomic information, including unfinished sequence data, are becoming increasingly important. We supplement our printed comparative analysis with a new, Web-based program called Laj (local alignments with java). Laj provides interactive access to archived pairwise sequence alignments via the WWW. It displays synchronized views of a dot-plot, a percent identity plot, a nucleotide-level local alignment and a variety of relevant annotations. Our mouse-human comparison can be viewed at http://web.uvic.ca/~bioweb/laj.html. Laj is available at http://bio.cse.psu.edu/, along with online documentation and additional examples of annotated genomic regions.

Systematic characterization of sperm-specific membrane proteins in swine

To establish a systematic strategy for characterizing fertilization proteins of sperm cells, we prepared alloantisera by immunizing gilts with salt-washed membranes from boar spermatozoa. The antisera recognized a unique subset of sperm membrane proteins that migrated with M(r) 7500-66,000 in SDS-PAGE under nonreducing conditions. The antisera did not recognize proteins of erythrocyte membranes, and tissue absorption experiments further confirmed that the alloantigens were sperm-specific proteins. Each of these sperm-specific membrane proteins (SSMPs) possessed one or more disulfide bonds that were essential for its interaction with alloantibody. Enzymatic deglycosylation revealed that most of the SSMPs were glycoproteins, and their alloantigenicity was not dependent on the presence of N-linked oligosaccharides. The presence of disulfide bonds and glycosylation indicated that the SSMPs identified each comprise at least one extracellular domain. Two-dimensional electrophoresis resolved at least 14 distinct SSMPs, 13 of which possessed acidic pIs (range 4.2-4.8). By indirect immunofluorescence, the SSMPs localized to the cell surface overlying all major regions of the sperm cell. We conclude that the repertoire of immunodominant SSMPs in the pig is relatively small, which makes feasible the systematic elucidation of their functions in fertilization.

Neuroendocrine consequences of fasting in adult male macaques: effects of recombinant rhesus macaque leptin infusion

Fasting inhibits the gonadotropic axis and stimulates the corticotropic and somatotropic axes. Since leptin is a product of fat cells that has been implicated in the control of both reproduction and metabolism, we hypothesized that the decrease in leptin observed during fasting was responsible for these effects on reproductive and metabolic hormones. Recombinant rhesus leptin (rrhLep) produced in our laboratory was infused (100 microgram/h) into fasted adult male rhesus macaques (6-9 kg) beginning at midnight after the first missed meal and continuing until the end of the study. Bioactive luteinizing hormone (LH), testosterone, cortisol and growth hormone (GH) were measured in plasma from samples collected at 15-min intervals for the last 15 h (42-57 h) of the fast. We analyzed pulsatile LH and GH secretion by deconvolution analysis and the orderliness of pulsatile LH and GH release by the approximate entropy (ApEn) statistic. There was no difference in LH pulse frequency between control and fasted groups, but there was a significant decrease in the mean concentration of LH released (7.6 +/- 1.4 ng/ml control vs. 2.7 +/- 0.65 ng/ml fasted) that was not relieved with rrhLep infusions (2.8 +/- 0.83 ng/ml). Model-free Cluster analysis confirmed these inferences and also indicated that the peak height was lower in the fasted (4.6 +/- 1.0 ng/ml) and the fasted + rrhLep (2.85 +/- 1.0 ng/ml) groups compared to controls (16. 3 +/- 1.4 ng/ml). Testosterone levels reflected those of LH. Fasting resulted in an increase in GH secretory pulse frequency (5.3 +/- 0. 95 pulses/15 h control vs. 12.8 +/- 1.4 pulses/15 h fasted) and this increase was not affected by rrhLep infusion (12.5 +/- 1.4 pulses/15 h). In addition, fasting also increased the ApEn (decreased the orderliness) of pulsatile GH secretion, and this characteristic was not relieved with rrhLep infusions. Cortisol levels in fasted animals were 2- to 3-fold higher than those observed in control studies, and this increase was particularly pronounced at the time when the animals expected their first meal of the day. The increase in circulating cortisol observed in fasted animals was not affected by rrhLep infusion. Glucose levels at the end of the sampling period were 80 mg/dl in controls, 48 mg/dl in fasted animals and 58 mg/dl in the fasted + rrhLep group. Circulating leptin levels averaged 1.2 +/- 0.37 ng/ml in control animals, 0.7 +/- 0.2 ng/ml in fasted animals and 10.1 +/- 5.6 ng/ml in fasted animals infused with rrhLep. These studies suggest that intravenous replacement with homologous leptin does not reverse the acute changes in GH, LH and cortisol secretion observed with fasting in the adult male macaque.

A sperm membrane protein that binds in a species-specific manner to the egg extracellular matrix is homologous to von Willebrand factor

We have purified a sperm membrane protein, designated zonadhesin, that binds in a species-specific manner to the extracellular matrix (zona pellucida) of the egg, and cloned its cDNA. The cDNA encodes a novel protein with a single transmembrane segment separating a 36 amino acid, highly basic intracellular C terminus from a 2418-amino acid extracellular region. The extracellular sequence specifies a mosaic protein comprising a unique N-terminal domain, a mucin-like domain, and five tandem domains proximal to the membrane that are homologous to prepro von Willebrand factor. The N-terminal and mucin-like domains were absent from zonadhesin that bound to the egg extracellular matrix, suggesting that processing occurs during sperm maturation and/or capacitation. By Northern blotting and in situ hybridization, zonadhesin mRNA was detected only within the testis, where it was expressed primarily in haploid spermatids. The unique domain structure of zonadhesin suggests multiple functions, one of which is to mediate sperm adhesion to the zona pellucida.

Species-specific binding of sperm proteins to the extracellular matrix (zona pellucida) of the egg

The zona pellucida is an extracellular matrix surrounding the mammalian egg where species-specific gamete recognition and signaling occur. Pig zona pellucida were isolated in large amounts and used as an affinity matrix for detergent-solubilized, biotinylated membrane proteins of pig spermatozoa. On non-reducing SDS-polyacrylamide gel electrophoresis, specifically bound sperm proteins migrated with M(r) 170,000, 150,000, 130,000, 56,000, and 50,000 (p50). Disulfide bond reduction separated each of the M(r) 130,000-170,000 proteins into M(r) 105,000 (p105) and M(r) 45,000 (p45) subunits, indicating that these high M(r) proteins are related. Based on two-dimensional electrophoresis, the M(r) 56,000 band was composed of three to four proteins that migrated with M(r) 56,000-62,000 (p56-62) in the second (reducing) dimension. p50 bound to heterologous zona pellucida (murine, bovine) and to Xenopus laevis oocyte envelopes, demonstrating a lack of species specificity to its binding and was identified as proacrosin/acrosin based on amino acid sequences of two tryptic peptides and its interaction with monospecific antibodies to proacrosin. In contrast, p105/p45 and one or more of the p56-62 proteins bound to pig zona pellucida but not to the egg extracellular matrices of the other species; these proteins therefore exhibited the species-specific binding to the zona pellucida expected for molecules involved in specific gamete adhesion. Amino acid sequences of nine tryptic peptides derived from p105/p45 did not match peptide sequences in existing databases, establishing it as a unique protein. These (p105/p45 and at least one p56-62 protein) are the first sperm membrane proteins to be identified that bind in a species-specific manner to the egg extracellular matrix.

Oviductin. Purification and properties of the oviductal protease that processes the molecular weight 43,000 glycoprotein of the Xenopus laevis egg envelope

The Xenopus laevis egg envelope is modified during egg transit through the pars recta oviduct. The physicochemical properties and ultrastructure of the envelope change, and the M(r) 43,000 envelope glycoprotein (gp43) is processed to M(r) 41,000. We purified a gp43 processing protease from oviductal secretory granules and studied its effects on the egg envelope. The M(r) 66,000 protease, designated oviductin, hydrolyzed the arginyl-X bond of N alpha-tert-butoxycarbonylphenylalanylserylarginyl-7-methylcoumaryl -4-amide (Km = 58 microM, kcat = 3.80 s-1). Diisopropyl fluorophosphate, EDTA, and EGTA inhibited oviductin irreversibly; soybean trypsin inhibitor, aprotinin, guanidine hydrochloride (Ki = 7.5 mM), and p-amino-benzamidine (Ki = 4.1 microM) also inhibited, but iodoacetamide, E-64, pepstatin, or 1,10-phenanthroline did not. The N-terminal amino acid sequence of oviductin was up to 64% identical to those of several serine proteases. Oviductin accounted for all of the gp43 processing activity we detected in secretory granules, and oviductin-catalyzed processing of gp43 rendered coelomic egg envelopes physically (as determined by thermal solubility) similar to those of oviposited eggs. We conclude (1) a unique serine protease secreted by the oviduct processes gp43 of the Xenopus laevis egg envelope, and (2) this processing causes physical changes in the egg envelope which occur during egg transit through the oviduct.

Maturation of guinea pig sperm in the epididymis involves the modification of proacrosin oligosaccharide side chains

Proacrosin from guinea pig cauda epididymal sperm has a lower molecular weight compared with the testicular zymogen. In this study, we have examined the structural basis of this change and where the conversion in proacrosin molecular weight occurs during sperm maturation. Immunoblotting of trifluoromethanesulfonic acid-deglycosylated testicular and cauda epididymal sperm extracts with antibody to guinea pig testicular proacrosin demonstrated that the polypeptide backbones of proacrosins from the testis and cauda epididymal sperm had the same molecular weights (approximately 44,000). Keratanase, an endo-beta-galactosidase specific for lactosaminoglycans, partially digested testicular proacrosin but had no effect on proacrosin from cauda epididymal sperm. In extracts of testis, caput epididymis, and corpus epididymis analyzed by immunoblotting, anti-proacrosin recognized a major antigen with an apparent molecular weight (Mr) of 55,000, although a 50,000-Mr minor antigen began to appear in the corpus epididymis. By contrast, extracts of cauda epididymis, vas deferens, and cauda epididymal sperm had the 50,000 Mr protein as the only immunoreactive antigen. By enzymography following electrophoresis, the major bands of proteolytic activity in extracts of testis, caput epididymis, and corpus epididymis had 55,000 Mr. A band of protease activity with 55,000 Mr also appeared in extracts of the corpus epididymis. However, the most prominent bands of proteolytic activity in cauda epididymis, vas deferens, and cauda epididymal sperm had 50,000 Mr. In addition, two other major protease activities were detected with 32,000 and 34,000 Mr; the relationships of these proteases to proacrosin are unclear. From these results, we conclude that the oligosaccharides of proacrosin are altered during epididymal transit and that this modification occurs in the corpus epididymis.(ABSTRACT TRUNCATED AT 250 WORDS)

Guinea pig proacrosin is synthesized principally by round spermatids and contains O-linked as well as N-linked oligosaccharide side chains

Proacrosin is the zymogen precursor of acrosin, a sperm protease believed to play an essential role in fertilization. In this study, we used primary cultures of guinea pig spermatogenic cells to examine the temporal appearance and mechanisms of synthesis and processing of proacrosin during acrosome development. Following [35S]methionine incorporation and immunoprecipitation, cultured spermatogenic cells were found to synthesize two forms of proacrosin (Mr 54,000 and 57,000). Proacrosin was synthesized mainly by round spermatids. By immunoblotting, proacrosin became very prominent in round spermatids and persisted throughout spermiogenesis. Pulse-chase experiments demonstrated that the Mr 54,000 form of proacrosin was converted to the Mr 57,000 form, presumably reflecting posttranslational processing of carbohydrate side chains. When spermatogenic cells were cultured in the presence of tunicamycin, the synthesized proacrosin had an Mr of 54,000. However, in vitro translation of mRNA extracted from guinea pig testis followed by immunoprecipitation indicated that the core polypeptide of proacrosin has an Mr of 44,000. Guinea pig spermatogenic cells incorporated glucosamine and fucose into the oligosaccharides of proacrosin. Treatment of guinea pig testis proacrosin with N-glycosidase or O-glycosidase reduced the Mr by 3-7%. These results indicate that proacrosin is synthesized by postmeiotic cells and the enzyme contains N- and O-linked oligosaccharides.

A mechanism for differential release of acrosomal enzymes during the acrosome reaction

To study the organization of fertilization enzymes in the sperm acrosome, we isolated and characterized two physicochemically distinct acrosomal fractions of guinea-pig spermatozoa. A soluble fraction contained the 25,000-Mr acrosomal autoantigen, AA1, and most of the acrosomal hyaluronidase and dipeptidyl peptidase II activity. A particulate fraction, designated acrosomal matrix (AM), consisted of membraneless crescent-shaped structures, and contained most of the acrosomal proacrosin. The AM also contained a 28,000-Mr putative proacrosin-binding protein, and a very-high-Mr component which, on reduction, was dissociated into 48,000-Mr and 67,000-Mr subunits. Autoproteolytic dissolution of the AM correlated with proteolysis by acrosin of the 28,000-Mr and 48,000-Mr AM molecules. Components of both the AM and the soluble fraction were localized by immuno-electron microscopy to the electron-dense region of the guinea-pig sperm acrosome. We conclude that acrosomal molecules are segregated into soluble and matrix compartments. This segregation is a function of disulphide bonding and non-covalent interactions among the relatively few components of the AM. Association of acrosin with the AM may be the mechanism by which this enzyme's release from the spermatozoon during the acrosome reaction is delayed relative to the release of other acrosomal molecules.

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.

Purification and characterization of the primary acrosomal autoantigen of guinea pig epididymal spermatozoa

Previous studies showed that sperm auto- and alloantigens participate in guinea pig (GP) fertilization. In an effort to determine how alloantibodies to GP sperm acrosomal contents (AC) inhibit fertilization, we identified acrosomal auto- and alloantigens using Western blots. The predominant autoantigens migrated with Mr = 25,000, Mr = 51,000, and Mr = 55,000 under nonreducing conditions. The primary (Mr = 25,000) acrosomal autoantigen, AA1, was purified to homogeneity from AC by gel filtration, cation-exchange chromatography, chromatofocusing, and a final gel filtration. We also purified AA1 from an acidic glycerol extract of spermatozoa by gel filtration, chromatofocusing, and high-performance liquid chromatography on hydroxylapatite. AA1 is a protein and shares at least one antigenic determinant with a 51,000 Mr acrosomal component. AA1 is acrosome-specific, as determined by immunoabsorption and by indirect immunofluorescence on testicular cells. By quantitative enzyme-linked immunosorbent assay, AA1 comprises 6.4% of acrosomal protein in GP spermatozoa. On the basis of its physiochemical properties and localization, we conclude that AA1 is a unique sperm autoantigen. Surprisingly, several antibody preparations, including allo- and heteroantibodies with high anti-AA1 titers, did not inhibit fertilization in vitro. Thus, the mechanism by which alloantibodies to AC inhibit GP fertilization in vitro is not by binding to AA1.

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.