Prostate-specific antigen in vaginal fluid as a biologic marker of condom failure

Forty women participated in three clinic visits during which they were exposed to their partner's semen (10 microL, 100 microL, and 1 mL). At each visit they took vaginal fluid samples before exposure to their partner's semen, immediately after, and at 1, 24, and 48 h after exposure. PSA was measured with an enzyme-linked immunoassay. The mean PSA level for preexposure swabs ranged between 0.43 and 0.88 ng/mL. The mean PSA levels were 193 immediately after exposure to 10 microL, 472 after 100 microL, and 19,098 after 1 mL. The PSA levels declined within 1 h, and returned to background at 48 h. The findings confirm that our procedure is a sensitive and specific method for detecting recent semen exposure, and indicate that PSA levels depend on exposure intensity and time since exposure. Application of this method in condom efficacy studies provides objective evidence of condom failure that enhances the interpretation of self-report.

Objective markers of condom failure

BACKGROUND

Studies of condom efficacy rely on self-reported behavior. Objective markers of exposure to semen may provide a more valid assessment of condom failure and failure to use condoms.

GOALS OF THIS STUDY

To compare three semen biomarkers: acid phosphatase (AP) activity, prostate specific antigen (PSA), and the human seminal plasma antigen (MHS-5).

STUDY DESIGN

Twenty women were intravaginally inoculated with six measured, increasingly larger amounts of their partners' semen. Vaginal fluid was collected by the participant using swabs and tested.

RESULTS

Background levels of PSA were low (0.00-1.25 ng/ml), background levels of AP were variable (0-350 U/l), and all preinoculation samples were negative for MHS-5. All postinoculation samples were positive for PSA, 64 of 117 (55%) for AP, and 14 of 120 (12%) for MHS-5.

CONCLUSION

The PSA immunoassay was the best semen biomarker under these sampling and testing conditions.

Sulfation of a tyrosine residue in the plasmin-binding domain of alpha 2-antiplasmin

Sulfation of human alpha 2-antiplasmin, the major plasma inhibitor of fibrinolysis, was examined using both protein isolated from human plasma and protein synthesized and biosynthetically labeled with [35S]sulfate by a human hepatoma-derived cell line. Linkage of sulfate to tyrosine was demonstrated by recovery of labeled tyrosine sulfate after base hydrolysis of sulfate-labeled alpha 2-antiplasmin. Analysis by reverse-phase high performance liquid chromatography of peptides released from alpha 2-antiplasmin by cleavage with trypsin or cyanogen bromide indicated that sulfate is linked to a single segment of the protein. A cyanogen bromide peptide corresponding to the sulfate-labeled peptide was prepared from alpha 2-antiplasmin isolated from human plasma. Consistent with the presence of tyrosine sulfate in this peptide, its chromatographic elution was altered by treatment with acid under conditions which release sulfate from a tyrosine residue. No peptide in the total digest of alpha 2-antiplasmin by cyanogen bromide eluted at the position of the peptide following desulfation, suggesting that all of the protein is in a sulfated form. The sequence of the sulfate-containing cyanogen bromide peptide as determined by sequential Edman degradation, amino acid composition, and fast atom-bombardment-mass spectrometry was: Glu-Glu-Asp-Tyr(SO4)-Pro-Gln-Phe-Gly-Ser-Pro-Lys-COOH. This peptide is a segment of the previously identified plasmin-binding domain of alpha 2-antiplasmin.

Identification of two sites of sulfation of human heparin cofactor II

Tyrosine sulfate was identified as a constituent of human heparin cofactor II by analysis of sulfate-labeled protein secreted by a human hepatoma-derived cell line and of purified protein from human plasma. Alkaline hydrolysis of heparin cofactor II released tyrosine sulfate as demonstrated by anion-exchange high performance liquid chromatography of hydrolysates. Two sites of sulfation were identified, and the amino acid sequences of the sites were established by sequential Edman degradation of sulfate-containing tryptic peptides that were isolated by reverse-phase high performance liquid chromatography. Each peptide contains only a single tyrosine residue so that the sites of sulfation can be assigned unambiguously. The two sites of sulfation are separated by 13 residues and represent an internal sequence repeat in the heparin cofactor II molecule. The two sites have the following sequences. Glu56-Asp-Asp-Asp-Tyr(SO4)-Leu-Asp62 Glu69-Asp-Asp-Asp-Tyr(SO4)-Ile-Asp75 Sulfate-labeled heparin cofactor II formed a covalent complex with thrombin in a heparin-dependent manner. Thus, the sulfate-containing form of the protein was shown to be biologically active. The characteristic sulfate-containing segment of heparin cofactor II, which contains 17 acidic amino acid residues over a span of 30 residues, may contribute to the unique properties of this thrombin inhibitor.

Characterization of sites of tyrosine sulfation in proteins and criteria for predicting their occurrence

A wide variety of secretory proteins have recently been found to undergo post-translational sulfation of specific tyrosine residues. Here, amino acid sequences surrounding known sulfation sites in proteins are analyzed in order to identify factors which determine the specificity of sulfation. Several distinctive features of sulfation sites are identified, including: abundance of acidic amino acid residues, lack of basic residues, low hydropathy, absence of neighboring cysteine residues, lack of extended secondary structure. Rules are proposed for predicting likely sites of sulfation based on the amino acid sequence of a protein.

Electrophoretic assays of amylase isoenzymes and isoforms

Electrophoretic methods provide an effective means for analysis of amylase isoenzymes and isoforms. A wide variety of such techniques have been developed and reflect different applications and analytic objectives of different investigators. Virtually all of the available clinical data on amylase isoenzymes and isoforms has resulted from application of these methods. Recent identification of selective amylase inhibitors and of monoclonal antibodies to amylase isoenzymes holds promise of development of rapid routine clinical assays for amylase isoenzymes. Electrophoretic methods will have an important role in validating these new assays. Furthermore, at the present time, electrophoretic methods provide the best approach for analyzing isoforms of the pancreatic and salivary isoenzymes. This may be clinically important in patients with tumors, pancreatic pseudocysts, or macroamylasemia. Further clinical experience is needed to define the roles of the various assays that are now available for the estimation of amylase isoenzymes and isoforms in human samples.

Sequence analysis of the COOH terminus of the alpha-chain of the fourth component of human complement. Identification of the site of its extracellular cleavage

The predominant form of the fourth component of complement in human and murine plasma (C4p) has an Mr approximately 5,000 less than C4 secreted by hepatocytes or macrophages (C4s). Here we demonstrate that the difference in Mr results from excision of a peptide from the COOH terminus of the alpha-chain of C4s. The site of truncation of the alpha-chain of C4 in plasma was established by sequence analysis of the COOH-terminal cyanogen bromide fragment isolated by high performance liquid chromatography. Sequential Edman degradation, digestion with carboxypeptidase Y, analysis of amino acid composition, and partial sequence analysis of an overlapping tryptic peptide established the sequence of this peptide to be Glu-Ala-Asn-Glu-Asp-Tyr-Glu-Asp-Tyr-Glu-Tyr-Asp-Glu-Leu-Pro-Ala. Comparison of our results with reported sequences establishes the COOH-terminal alanine to be residue 748 in the alpha-chain. This identifies the site at which C4s is cleaved by an extracellular protease and suggests that the protease has an elastase-like activity.

Effects of acidotropic compounds on the secretory pathway: inhibition of secretion and processing of the third and fourth components of complement

Acidotropic compounds (also termed lysosomotropic) such as chloroquine and amantadine interfered with processing of the single-chain precursors to the third and fourth components of complement (C3 and C4) by the human hepatoma-derived cell line HepG2. When these compounds were added to culture medium, the precursors of C3 and C4 became the major secretory forms in contrast to the normal secretion of C3 and C4 as their mature forms. In addition, secretion of C3, C4, and total protein was inhibited by these compounds. Our results indicate that lysosomotropic agents, in addition to their well recognized effects on lysosomes and endosomes, inhibit functions of the secretory pathway.

Sulphation of proteins secreted by a human hepatoma-derived cell line. Sulphation of N-linked oligosaccharides on alpha 2HS-glycoprotein

Several human glycoproteins, including alpha 1-antitrypsin, alpha 1-acid glycoprotein, transferrin, caeruloplasmin and alpha 2HS-glycoprotein, synthesized by the hepatoma-derived cell line HepG2 were observed to contain covalently linked sulphate. These proteins were estimated to contain about 0.1 mol of sulphate/mol of protein. The most abundant of the sulphated glycoproteins, alpha 2HS-glycoprotein, was analysed in detail. All of the sulphate on this protein was attached to N-linked oligosaccharides which contained sialic acid and resisted release by endoglycosidase H. Several independent analytical approaches established that approx. 10% of the molecules of alpha 2HS-glycoprotein contained sulphate. Our results suggest that a number of human plasma proteins contain small amounts of sulphate linked to oligosaccharides.

Identification of the site of sulfation of the fourth component of human complement

The alpha-chain of the fourth component of complement (C4) contains tyrosine sulfate (Karp, D.R. (1983) J. Biol. Chem. 258, 12745-12748). Here we have determined the site and stoichiometry of sulfation of C4 secreted by the human hepatoma-derived cell line Hep G2. C4 was labeled with [35S]sulfate and isolated from culture medium by immunoprecipitation. C4 digested with trypsin and chymotrypsin and analyzed by reverse-phase high-performance liquid chromatography contained a single sulfate-labeled peptide. Digestion of C4 with trypsin alone yielded two major sulfate-labeled peptides, suggesting that there may be some sequence variability in C4 near the site of sulfation. Sequential Edman degradation of tryptic peptides labeled with [3H]tyrosine and [35S]sulfate detected tyrosine residues at positions 5, 13, 16, and 18. Chymotrypsin cleaved 5 residues off the NH2-terminal end of tryptic peptides, yielding a peptide with tyrosine at positions 8, 11, and 13. Comparison of the position of tyrosine residues with the reported sequence of C4 identified the sites of sulfation as tyrosine residues at positions 738, 741, and 743 in the alpha-chain of C4. All 3 of these tyrosine residues appeared to be sulfated. When sulfation of C4 was partially inhibited by addition of catechol to culture medium, three different forms of the peptide were resolved by high-performance liquid chromatography, consistent with peptides containing 1, 2, or 3 sulfates. Comparison of the quantities of tyrosine and tyrosine sulfate in C4 which had been labeled with [3H]tyrosine and digested with Pronase also indicated that C4 contained an average of 2-3 residues of tyrosine sulfate/molecule. These results suggest that the biologically active form of the protein is sulfated.

Variable denaturation of ovalbumin by incorporation of amino acid analogs

Denaturation of hen ovalbumin synthesized in a cell-free system was assayed by examining its sensitivity to trypsin. The native ovalbumin resisted digestion by trypsin, and it remained resistant to digestion when some amino acid analogs, including azetidine-2-carboxylic acid and meta-flourotyrosine, were incorporated into its peptide chain. However, when other amino acid analogs such as beta-hydroxyleucine and 4-thiaisoleucine were incorporated during protein systhesis, ovalbumin became very lablie to trypsin. These experiments demonstrate a sensitive system for detecting protein denaturation and suggest a variable effect of different amino acid analogs on the native conformation of a protein.

DL-threo-beta-fluoroasparagine inhibits asparagine-linked glycosylation in cell-free lysates

The effect of beta-fluoroasparagine on N-linked glycosylation was examined in a cell-free translation system in which glycosylation is coupled to protein synthesis. The threo-isomer markedly inhibited glycosylation at a concentration of 1 mM, and this effect was blocked by L-asparagine, indicating that glycosylation was inhibited secondary to incorporation of the asparagine analog into protein. The erythro-isomer, at similar concentrations, was not incorporated into protein and had no effect on glycosylation. threo-beta-Fluoroasparagine is highly toxic to some mammalian cells in culture. Our observations suggest that its toxicity may be due in part to the failure of the fluoroasparagine-containing protein to become glycosylated. The data suggest that this analog will be useful for examining the structural determinants for glycosylation.

Rat pro-opiomelanocortin contains sulfate

Intermediate lobes isolated from rat pituitary glands incorporated [35S]sulfate into pro-opiomelanocortin and other adrenocorticotropic hormone-containing peptides. Incubation of intermediate lobes in medium containing the arginine analog canavanine inhibited the cleavage of pro-opiomelanocortin into smaller products. Pro-opiomelanocortin that accumulated in the presence of canavanine was also sulfated.

Metabolic labeling of lutropin with [35S]sulfate

Chemical analyses have previously detected sulfate linked to the oligosaccharides of lutropin isolated from bovine and human pituitaries. To determine whether lutropin could be metabolically labeled with sulfate, isolated bovine and rat pituitaries were incubated with [35S]sulfate. In both species, two major labeled products were immunoprecipitated with antisera specific to lutropin subunits. Incorporation into the subunits occurred posttranslationally since it was not blocked by cycloheximide, which did, however, block the incorporation of radiolabeled methionine. Metabolic labeling with [35S]sulfate provides a valuable approach for examining the biosynthetic processing of lutropin and the physiological role of sulfate in this hormone.

Miscleavage at the presequence of rat preprolactin synthesized in pituitary cells incubated with a threonine analog

We have shown previously that processing of preprolactin to prolactin in isolated rat pituitaries is inhibited by the threonine analog, beta-hydroxynorvaline (Hnv), presumably because of its substitution for the threonine at the cleavage site. Here, we show by amino-terminal sequence analyses that Hnv altered the site at which preprolactin produced had three extra amino acids at the amino terminus. The miscleaved prolactin was secreted into the medium, and there was a delay of approximately 5 min between the initial appearance of prolactin and the formation of miscleaved prolactin. This lag period suggests that miscleaved prolactin did not represent an intermediate in the normal processing of preprolactin but resulted from cleavage of completed preprolactin chains containing Hnv. These results show that modification of the structure of a preprotein can alter the site of its cleavage. One site that appears to be critical for correct cleavage is the final amino acid residue in the prepeptide. The data also indicate that complete removal of the presequence is not required for secretion of a protein.

Transport of an uncleaved preprotein into the endoplasmic reticulum of rat pituitary cells

Preprolactin (Pre-Prl) accumulates isolated rat pituitaries incubated with the threonine analog, beta-hydroxynorvaline. The present study examined whether the failure to cleave Pre-Prl to prolactin inhibits the translocation of the peptide chain across the membrane of the endoplasmic reticulum. In homogenates of pituitary tissue Pre-Prl, prolactin, and growth hormone were not degraded by added proteases. If 0.1% Triton X-100 was added with the proteases these proteins were degraded, suggesting that protection of these proteins from proteases was conferred by membrane vesicles. When Pre-Prl synthesized in a cell-free system was mixed and homogenized with pituitary tissue, it was completely degraded by these enzymes. Thus, protease-resistant Pre-Prl was not the result of nonspecific vesicular entrapment of free Pre-Prl during homogenization. Pre-Prl synthesized in isolated pituitaries copurified with the membrane fraction when the vesicles were isolated from tissue homogenates by flotation in 60% sucrose, and sonication and low concentrations of detergent released Pre-Prl from this fraction. Thus, removal of the prepeptide is not an essential step for the insertion of secretory proteins into the endoplasmic reticulum.

Inhibition of asparagine-linked glycosylation by incorporation of a threonine analog into nascent peptide chains

The importance of threonine in the Asn-X-Thr recognition sequence for asparagine-linked glycosylation was tested by examining the effect of a threonine analog, beta-hydroxynorvaline, on co-translational glycosylation in Krebs' II ascites tumor lysates. beta-Hydroxynorvaline inhibited the glycosylation of the alpha subunit of human chorionic gonadotropin and the beta subunit of bovine luteinizing hormone; both proteins contain Asn-X-Thr recognition sites. The effect was prevented by threonine, indicating that beta-hydroxynorvaline acted via its incorporation into protein. These results provide direct evidence for the role of threonine in Asn-X-Thr sites for asparagine-linked glycosylation. The results support the view that this site is sensitive to steric hindrance.

Pre-prolactin accumulates in rat pituitary cells incubated with a threonine analog

The proteolytic processing of rat pre-prolactin (Pre-Prl) to prolactin in isolated hemipituitaries was inhibited by the threonine analog, beta-hydroxynorvaline (Hnv). Pre-Prl accumulated as a major labeled intracellular product, even during pulse labeling longer than 2 h, but it was not secreted. Inhibition of Pre-Prl processing may result from incorporation of Hnv at the Pre-Prl cleavage site. This system offers the opportunity to study the disposition of an accumulated pre-protein in cells.

Inhibition of preprotein processing in ascites tumor lysates by incorporation of a leucine analog

Leucine analogs were tested in the Krebs II ascites cell-free translation system for the ability to inhibit preprotein cleavage by replacing leucine in nascent chains of bovine preprolactin, rat preprolactin, human placental prelactogen (pre-hPL), and pre-alpha subunit of human chorionic gonadotropin (alpha-hCG). In the absence of analog, ascites microsomal membranes cleaved these preproteins to their mature forms and sequestered the processed products. Also, two asparagine residues in alpha-hCG were glycosylated. When 4 mM beta-DL-hydroxyleucine was added to the lysate instead of L-leucine, cotranslational processing and sequestration of both species of preprolactin and pre-hPL were inhibited. Sequential Edman degradation confirmed that pre-hPL was not cleaved. The inhibition of processing by beta-hydroxyleucine resulted from its incorporation into protein. This was shown by reversal of the effect by addition of leucine and by inhibition of [(3)H]leucine incorporation into protein. Of significance, the processing of pre-alpha-hCG was less sensitive to beta-hydroxyleucine because its prepeptide contains only four scattered leucine residues, whereas the presegments of hPL and the prolactins contain six to eight clustered leucine residues. These experiments demonstrate that translocation and processing of secretory proteins require structural features determined by the primary amino acid sequence.