Studies on cystic fibrosis using isoelectric focusing. II. Demonstration of deficient proteolytic cleavage of alpha2-macroglobulin in cystic fibrosis plasma.

A protein with an isoelectric point (pI) of 5.48 was found to 
be deficient in plasma from most cystic fibrosis (CF) homozygotes and 
obligate heterozygote carriers of CF as compared with normal control plasma. 
Purification of the protein with a pI of 5.48 from normal 
plasma was performed using ammonium sulfate precipitation, DEAE- cellulose and CM-cellulose 
chromatography, Sephadex G-200- gel filtration, starch block electrophoresis, and Sepharose 4B 
gel filtration. The purified protein migrated as a single band on 
polyacrylamide gel electrophoresis, and displayed a single arc on immunoelectrophoresis against 
polyvalent antiserum to whole human serum. Results from various techniques used 
in its characterization indicate that this protein is a fragment of 
alpha2-macroglobulin (alpha2M) which is derived from alpha2M by proteolytic cleavage of 
intact alpha2M subunits. Quantitation of alpha2M levels in plasma indicated no 
significant differences between levels of alpha2M in CF homozygote, obligate heterozygote 
carrier, or normal control plasma samples. Quantitation of arginine esterase activity 
in plasma treated with cloroform and ellagic acid indicated that both 
the total arginine esterase activity and that fraction of arginine esterase 
activity inhibited by soybean trypsin inhibitor (SBTI) were decreased in most 
CF homozygote and obligate heterozygote plasma samples relative to normal control 
values. The results of this study indicate that plasma samples from 
CF homozygotes and obligate heterozygote carriers for CF show deficient proteolytic 
cleavage of alpha2M as compared with normal control plasma, and suggest 
that a structural abnormality in alpha2M or a deficiency in plasma 
proteolytic activity may be responsible for this deficiency in proteolysis. 