Comparison between purified alpha2-macroglobulin preparations from normal controls and patients with cystic fibrosis. Kinetic and structural properties of the complex with bovine trypsin.

Alpha-2-macroglobulin was purified from plasma obtained from three healthy controls and three 
patients with cystic fibrosis. The normal and patient preparations were indistinguishable 
antigenically and in their UV absorption spectra. Competitive inhibition by these 
preparations of the hydrolysis of benzoyl-L-arginine ethyl ester by bovine trypsin 
was observed. The Ki value for normal alpha-2-macroglobulin was 5.3 x 
10-8 M as compared to 1.8 x 10-7 M for cystic 
fibrosis patients preparations. The km values of the alpha-2-macroglobulin-trypsin complex were 
6.3 x 10-4 M for the normal protein and 1.5 x 
10-4 M with the alpha-2-macroglobulin from the cystic fibrosis patients. Gel 
chromatography of normal alpha-2-macroglobulin, preincubated in molar ratios with bovine trypsin, 
revealed the formation of alpha-2-macroglobulin fragments. These fragments were not obtained 
with the preparations from the cystic fibrosis patients. Both the normal 
and cystic fibrosis alpha-2-macroglobulins were shown by gel chromatography in sodium 
dodecyl sulfate to be tetramers, noncovalently bound. After reduction and alkylation 
the monomers were found to be a single polypeptide chain. The 
fragments obtained by preincubating normal alpha-2-macroglobulin with trypsin had approximately half 
the molecular weight of the intact monomer. Cystic fibrosis alpha-2-macroglobulin preincubated 
with trypsin in sodium dodecyl sulfate a single major component identical 
to the intact monomers, with no formation of alpha-2-macroglobulin fragments. 