Affinity chromatographic purification of the pregnancy zone protein

The use of selective adsorbents in capillary electrophoresis-mass spectrometry for analyte preconcentration and microreactions: a powerful three-dimensional tool for multiple chemical and biological applications

Much attention has recently been directed to the development and application of online sample preconcentration and microreactions in capillary electrophoresis using selective adsorbents based on chemical or biological specificity. The basic principle involves two interacting chemical or biological systems with high selectivity and affinity for each other. These molecular interactions in nature usually involve noncovalent and reversible chemical processes. Properly bound to a solid support, an "affinity ligand" can selectively adsorb a "target analyte" found in a simple or complex mixture at a wide range of concentrations. As a result, the isolated analyte is enriched and highly purified. When this affinity technique, allowing noncovalent chemical interactions and biochemical reactions to occur, is coupled on-line to high-resolution capillary electrophoresis and mass spectrometry, a powerful tool of chemical and biological information is created. This paper describes the concept of biological recognition and affinity interaction on-line with high-resolution separation, the fabrication of an "analyte concentrator-microreactor", optimization conditions of adsorption and desorption, the coupling to mass spectrometry, and various applications of clinical and pharmaceutical interest.

A procedure for human pregnancy zone protein (and human alpha 2-macroglobulin) purification using hydrophobic interaction chromatography on phenyl-sepharose CL-4B column

In the present work we describe a procedure for the purification of human pregnancy zone protein (PZP) from pooled late pregnancy plasma by using hydrophobic interaction chromatography (HIC) on a phenyl-Sepharose column. The HIC step allowed the complete isolation of haptoglobins and the partial separation of human alpha 2-macroglobulin (alpha 2-M) from a protein fraction containing PZP previously obtained by a DEAE-Sephacel chromatography. Pure and native PZP, with a recovery of nearly 25% and biological activity of protease-binding, was obtained by two definitive final steps consisting of zinc-chelate and size-filtration chromatographies. Moreover, we further present an alternative procedure for the purification of alpha 2-M from the same pregnancy plasma, based on the differential elution of PZP and alpha 2-M from the HIC. This purification step gave rise to a highly purified product with a recovery of 10%. This differential elution could be explained by differences in surface hydrophobicity observed between both proteins. In addition, considering the different hydrophobic properties exhibited by native PZP and PZP-protease complexes, HIC on phenyl-Sepharose column could also be used for separating both conformational states of PZP.

Immunohistochemical definition of antigenic determinants of pregnancy-associated alpha 2-glycoprotein (alpha 2-PAG) using monoclonal antibodies

Human pregnancy-associated alpha 2-glycoprotein (alpha 2-PAG) is a high molecular weight glycoprotein in normal sera. The protein is present in high concentration in the sera of pregnant females and in abnormally low concentration in association with conditions connected with abnormalities of mucosal immunity. Indirect immunoperoxidase techniques using poly- and monoclonal antibodies were employed to identify pregnancy-associated alpha 2-PAG in different tissues. Four monoclonal antibodies were selected from a battery of antibodies with defined specificities in order to ascertain reactivity with various epitopes of the antigen. The antibodies were applied to paraffin sections of breast, colon, salivary gland, and tonsil, and different fixation regimes were used in the preparation of the tissues. The polyclonal antibodies were found to stain plasma cells and epithelial lumina evenly in all the tissues included whereas the monoclonal antibodies were shown to stain certain components selectively. In breast and salivary glands, all four monoclonal antibodies could identify alpha 2-PAG, but in tonsil and colon, only two were reactive. This difference in epitope expression might reflect the internal processing of alpha 2-PAG, and lack of availability of certain epitopes may be indicative of functional blocking of certain domains.

A two-site monoclonal enzyme immunoassay for pregnancy-associated alpha 2-glycoprotein

A two-site monoclonal enzyme immunoassay (MEIA) was developed for the determination of pregnancy-associated alpha 2-glycoprotein (PA alpha 2G) in serum. The minimum detectable level was 35 ng/ml. No immunochemical interaction with the closely related alpha 2-macroglobulin was found. Serum levels in 145 normal healthy males and non-pregnant females were 1.8 +/- 2.8 micrograms/ml (mean +/- SD), respectively, both significantly lower than previously reported. The distribution in the normal population was characteristically different when males and females were compared. No increase with age was found. During pregnancy, a significant increase in serum concentration was observed with average levels of 320 +/- 200 micrograms/ml at term (mean +/- SD), a 50-fold increase in concentration. As a tumor marker for breast and ovarian cancer, PA alpha 2G was found to be of no value. The present study emphasizes that a reevaluation of PA alpha 2G levels must be undertaken in order to assess the clinical and biological significance of this protein.

Antigenic determinants of pregnancy-associated alpha 2-glycoprotein and alpha 2-macroglobulin defined by poly- and monoclonal antibodies

Human alpha 2-macroglobulin and pregnancy-associated alpha 2-glycoprotein (PA alpha 2G) share several physicochemical characteristics. By the use of unabsorbed or absorbed polyclonal antibodies to these antigens, the existence of common epitopes in these molecules were demonstrated in crossed immunoelectrophoresis. Two monoclonal antibodies out of 9 raised against purified PA alpha 2G were demonstrated to react with both antigens, indicating close immunochemical relatedness between these macroglobulins. The findings might have functional implications.

Partial primary structure of human pregnancy zone protein: extensive sequence homology with human alpha 2-macroglobulin

Human pregnancy zone protein (PZP) is a major pregnancy-associated protein. Its quaternary structure (two covalently bound 180-kDa subunits, which are further non-covalently assembled into a tetramer of 720 kDa) is similar to that of human alpha 2-macroglobulin (alpha 2M). Here we show, from the results of complete or partial sequence determination of a random selection of 38 tryptic peptides covering 685 residues of the subunit of PZP, that PZP and alpha 2M indeed are extensively homologous. In the stretches of PZP sequenced so far, the degree of identically placed residues in the two proteins is 68%, indicating a close evolutionary relationship between PZP and alpha 2M. Although the function of PZP in pregnancy is largely unknown, its close structural relationship to alpha 2M suggests analogous proteinase binding properties and a potential for being taken up in cells by receptor-mediated endocytosis. In this regard our studies indicate a bait region in PZP significantly different from that present in alpha 2M. PZP could be the human equivalent of the acute-phase alpha-macroglobulins (e.g., rat alpha 2M and rabbit alpha 1M) described earlier.

Quantification of corticosteroid binding globulin by electroimmunoassay during human pregnancy

Corticosteroid binding globulin (CBG) was purified by one step positive immunospecific affinity chromatography and antibody to human CBG produced in goats. The goat anti-human CBG was used in the development of a precise rocket immunoelectrophoresis for CBG quantification. CBG levels measured by this assay were found to increase from 30 AU/ml to 100 AU/ml during pregnancy. There was no statistically significant association observed between levels of CBG, or circulating estriol, or pregnancy zone protein. Circulating CBG was estimated in 32 women with pregnancy associated hypertension, the levels were all within the normal range, and not significantly different from those seen in matched controls.

Comparison of pregnancy-associated murine protein-1 and human pregnancy zone protein

Immunological cross-reaction between human pregnancy zone protein (PZP, SP-3, alpha 2-PAG) and pregnancy-associated murine protein-1 (PAMP-1) was demonstrated by countercurrent line immunoelectrophoresis using antibodies against the proteins raised in hens. The levels of PZP and PAMP-1 were measured during pregnancy and found to be very similar in the first half of pregnancy. Both proteins were found to be heterogeneous and separable according to surface properties. It is suggested that the murine PAMP-1 can be used to study the physiology of human PZP.

Circulating levels of pregnancy zone protein: normal range and the influence of age and gender

Serum levels of pregnancy zone protein (PZP) were measured in 506 apparently normal males and 329 normal non-pregnant females, the age range being 18 to 70 years. The estimations of PZP were performed by sensitive radio-rocket-line immunoelectrophoresis. The distribution of the data had a marked positive skew in both sexes which was reduced following logarithmic transformation. Serum concentrations in both men and women were found to increase significantly with advancing age. This increase and the mean concentrations were significantly higher in females.

A method for preparation of immunosorbents by direct coupling of dissociated immune complexes

A simple and rapid method of preparing immunosorbents by use of isolated immune complexes is described. Dissociated immune complexes may be directly coupled to activated Sepharose and an immunosorbent gel with complementary molecular populations of immunospecifically purified ligands is obtained. The antigen binding capacity of insolubilized antibodies was about 50% of the antigen bound at equivalence using liquid phase precipitation. The batch technique described may be scaled up and the only limitation is the availability of the ligands. The usefulness of the technique is illustrated in two model systems.

An automatic multi-programmed affinity chromatographic system

An automatic immunospecific affinity-chromatographic system for continuous operation is described. The system comprises time-controlled sample application, washing and elution steps and automatic dialysis of eluted fractions. The applicability of the system is illustrated by the purification of pregnancy zone protein on immunosorbent gel.