Isolation and characterization of circulating complex between human pregnancy-associated plasma protein-A and proform of eosinophil major basic protein.
The plasma protein previously known as pregnancy associated plasma protein-A (PAPP-A) and believed to contain only one kind of polypeptide chain has recently been shown to be a complex containing two different chains in equimolar amounts. One of the chains is now defined as the PAPP-A subunit, and the other has been identified as the proform of eosinophil major basic protein (proMBP) (Oxvig et al. (1993) J. Biol. Chem. 268, 12243-12246). A procedure for large scale preparation of the circulating complex (PAPP-A/proMBP) from pooled pregnancy serum is described. The amino acid and carbohydrate compositions of the isolated reduced and carboxymethylated PAPP-A (199 kDa) and proMBP subunits (38 kDa), and of the intact PAPP-A/proMBP have been determined. The PAPP-A and proMBP subunits contain 13.4% (w/w) and 38.6% (w/w) carbohydrate, respectively, and the intact complex contains 17.4% (w/w) carbohydrate. The PAPP-A subunit contains N-bound carbohydrate groups. In contrast, the proMBP subunit contains both N- and O-bound groups as well as glycosaminoglycan, previously found among plasma proteins only in inter-alpha-trypsin inhibitor and pre-alpha-trypsin inhibitor. It is shown that PAPP-A/proMBP can competitively inhibit human leucocyte elastase (KI = (5-10) x 10(-9) M) at an ionic strength of 0.075, but the inhibition is negligible at ionic strengths greater than 0.15. Human cathepsin G is also competitively inhibited (KI approx. 1 x 10(-6) M). The inhibition of both enzymes is most likely due to interactions with the glycosaminoglycan moiety of PAPP-A/proMBP. It is concluded that PAPP-A/proMBP is neither a potent nor a specific inhibitor of human leucocyte elastase.
Oxvig
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C
Department of Molecular Biology, University of Aarhus, Denmark.
Sand
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O
Kristensen
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T
Kristensen
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Sottrup-Jensen
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L
D000596:Amino Acids / Q000032:analysis; D001798:Blood Proteins / Q000302:isolation & purification*; D002241:Carbohydrates / Q000032:analysis; D047091:Eosinophil Granule Proteins; D006801:Humans; D011266:Pregnancy-Associated Plasma Protein-A / Q000302:isolation & purification*; D011480:Protease Inhibitors / Q000097:blood* / Q000302:isolation & purification; D011498:Protein Precursors / Q000097:blood* / Q000302:isolation & purification; D012260:Ribonucleases
D000596:Amino Acids; D001798:Blood Proteins; D002241:Carbohydrates; D047091:Eosinophil Granule Proteins; D011480:Protease Inhibitors; D011498:Protein Precursors; D012260:Ribonucleases; D011266:Pregnancy-Associated Plasma Protein-A