Pregnancy zone protein, a proteinase-binding macroglobulin. Interactions with proteinases and methylamine.
Human pregnancy zone protein (PZP) is a major pregnancy-associated plasma protein, strongly related to alpha 2-macroglobulin (alpha 2M). Its properties and its reactions with a number of enzymes, particularly chymotrypsin, and with methylamine have been investigated. It is concluded that native PZP molecules are dimers of disulfide-bridged 180-kDa subunits and that proteinase binding results in covalent 1:1 (tetrameric)PZP-enzyme complexes. Native PZP is unstable, and storage should be avoided, but when kept unfrozen at 0 degree C most PZP preparations stay native 1-3 months. The reaction of PZP with chymotrypsin involves (i) proteolysis of bait regions, (ii) cleavage of beta-cysteinyl-gamma-glutamyl thiol ester groups, (iii) some change of the conformation and quaternary structure of PZP, and (iv) the formation of covalent 1:1 chymotrypsin-PZP(tetramer) complexes in which chymotrypsin is active but shows less activity than free chymotrypsin. The emission spectra of intrinsic fluorescence show significant differences between the PZP-chymotrypsin complex and its native components, whereas no differences are observed between methylamine-reacted PZP and native PZP. Methylamine reacts with the beta-cysteinyl-gamma-glutamyl thiol ester groups of PZP in a second-order process with k = (13.6 +/- 0.5) M-1 s-1, pH 7.6, 25 degrees C. The reaction product is PZP(dimers); no PZP(tetramers) are formed. The proteinase-binding specificity of PZP is far more restricted than that of alpha 2M. Certain chymotrypsin-like and trypsin-like enzymes are bound much less efficiently than is chymotrypsin itself.(ABSTRACT TRUNCATED AT 250 WORDS)
Christensen
U
U
Kemisk Laboratorium IV, University of Copenhagen, Denmark.
Simonsen
M
M
Harrit
N
N
Sottrup-Jensen
L
L
D002918:Chymotrypsin / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000378:metabolism*; D005260:Female; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008744:Methylamines / Q000378:metabolism*; D011247:Pregnancy; D011257:Pregnancy Proteins / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D013438:Sulfhydryl Compounds / Q000378:metabolism
D046911:Macromolecular Substances; D008744:Methylamines; D011257:Pregnancy Proteins; D013438:Sulfhydryl Compounds; D010450:Endopeptidases; D002918:Chymotrypsin