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-proteinase complexes in cystic fibrosis serum. Analysis by monoclonal antibodies and receptor-mediated endocytosis by normal human fibroblasts

alpha 2-Macroglobulin complexed to proteinases activated during clotting of cystic fibrosis and control sera was quantitated with the complex-specific monoclonal antibody F2B2 . Similar amounts of alpha 2-macroglobulin complexes (between 40 and 90 micrograms/ml) were generated in cystic fibrosis and control sera. Endocytosis of the complexes by normal human fibroblasts was compared to the amount of complexes detected by the F2B2 -radioimmunoassay. Normal uptake was observed with 13 out of 14 cystic fibrosis sera. One cystic fibrosis serum showed strongly reduced endocytosis of the complexes. Complexes isolated from this serum on immobilized F2B2 failed to inhibit binding of purified alpha 2-macroglobulin-trypsin to its receptor, demonstrating deficient receptor-binding of these complexes. The low uptake complexes could not be distinguished from complexes isolated from control or other cystic fibrosis sera by isoelectric focusing, rate electrophoresis or SDS-polyacrylamide gel electrophoresis.

Characterization of alpha 2-macroglobulin from plasma of cystic fibrosis patients and controls

The physical, kinetic, and isoelectric focusing properties of native alpha 2-macroglobulin from cystic fibrosis and control plasmas were studied. No differences were found in the esterolytic activity levels of control, obligate heterozygote, and cystic fibrosis plasmas. Stability studies indicated that both control and cystic fibrosis alpha 2-macroglobulin retained full activity for at least 8 months at -20 degrees C, a week at 0-4 degrees C, 11 hr at 50 degrees C, and showed no differences in thermostability at several preincubation temperatures. The microheterogeneity of native alpha 2-macroglobulin was studied by column isoelectric focusing of five control and five cystic fibrosis plasmas. The number and pI values of the isoelectric forms between pH 4.5-8.0 were quite similar for both groups even though consistently less cystic fibrosis alpha 2-macroglobulin activity was recovered after isoelectric focusing.

Systematic study of the hydrolysis of 4-methylumbelliferylguanidinobenzoate in plasma from patients with cystic fibrosis and controls

In contrast to the original reports by others, the hydrolysis of 4-methylumbelliferylguanidinobenzoate ((MUGB), and active-site titrant of serine proteases, was found not to be significantly different in plasma samples from patients with cystic fibrosis (CF), obligate heterozygotes, and normal controls. Since the steady-state turnover of substrate is the dominant term of MUGB hydrolysis, the assay in its present form does not meet the requirements of an active-site titration. The reproducibility and reliability of the assay are hampered by (1) high blank values due to non-specific hydrolysis, (2) the absence of a defined endpoint of the incubation, (3) the non-linearity of the assay with respect to plasma concentration, (4) the temperature-dependent evolution of esterase activity during incubation, and (5) most importantly the loss of activity during storage of plasma samples. Cleavage of MUGB catalysed by the imidazole ring of histidine accounts for a significant portion of the activity in plasma.

Protease binding by alpha 2 macroglobulin in cystic fibrosis

The interaction of alpha 2 macroglobulin (alpha 2M) with exogenous proteases has been reported by others to be abnormal in cystic fibrosis (CF). We have re-examined these claims. Four parameters were considered:(1) the molar protease binding of alpha 2M; (2) the interaction of bovine cationic trypsin (BCT), complexed to alpha 2M, with low molecular mass substrate, benzoyl arginine ethyl ester (BAEE); (3) the stability of formed alpha 2 M-BCT complexes; and (4) the subunit structure of alpha 2M. We have found CF alpha 2M to be similar to control alpha 2M in every respect studied.

Altered regulation of a proteinase mediated primary secretion processing system as the basic defect in cystic fibrosis

Depsite the high incidence of cystic fibrosis there is no clear cut direction to research into the basic defect responsible for this disorder. This is, at least in part, due to the exceptional amount of irreproducibility surrounding the disease. The defective ion reabsorption in CF sweat glands may be a prototype of a generalized failure to correctly process exocrine gland primary secretions. Such a physiological defect could account for many of the clinical symptoms of CF. It is hypothesised that one or more secreted proteinase(s) may mediate the events of secretion processing. A mutation in the structural gene for such a proteinase or a regulating anti-proteinase or some enzyme carrying out a functionally important post translational modification of the proteinase would then account for the disease.

Purification and characterization of alpha 1-antichymotrypsin from human pleural fluid and human serum

Human alpha 1-antichymotrypsin was purified from human pleural fluid and from human serum. Four affinity chromatographic steps were required to obtain pure alpha 1-antichymotrypsin. Pleural and serum alpha 1-antichymotrypsin have the same molecular weight, which was estimated by SDS-polyacrylamide gel electrophoresis to be 58 000. The chemical composition of the two types of alpha 1-antichymotrypsin is the same. Using a technique for visualization of the chymotrypsin inhibitors, we showed that the pure alpha 1-antichymotrypsin obtained from the two physiological fluids had its inhibitory capacity preserved.

Studies on the complex between human alpha 2-macroglobulin and Crotalus adamanteus proteinase II. Release of active proteinase from the complex

Proteinase II from Crotalus adamanteus venom formed a complex with human alpha 2-macroglobulin in which approx. 1.7 mol of enzyme were bound per mol inhibitor. The complex did not enzymatically inactivate human alpha 1 proteinase inhibitor. However, active proteinase II was released from the complex in the presence of a high molecular weight proteinase fraction from C. adamanteus venom. The alpha 2-macroglobulin-proteinase II complex was also unstable during incubation in serum, and the enzyme released from the complex caused inactivation of serum proteinase inhibitors. The results indicate conditions under which venom proteinases can be dissociated from their complexes with alpha 2-macroglobulin and thus remain functional in the presence of molar excesses of inhibitor.

Human alpha-2-macroglobulin. Studies on the electrophoretic heterogeneity

Purified alpha-2-macroglobulin may be resolved into as many as five electrophoretic bands on selected polyacrylamide gel systems. The microheterogeneity does not result from prior proteolytic attack but appears to correspond to different conformational states of the inhibitor. Trypsin binding capacity and the extent of subunit cleavage into 120,000 and 70,000 dalton fragments by mild alkaline treatment are related to the proportion of fast and slow electrophoretic forms. Study of proteinase binding after electrophoretic separation by special zymogram techniques confirms that the fastest electrophoretic form has very low binding capacity. No electrophoretic differences conld be observed in alpha-2-macroglobulin derived from cystic fibrosis plasma relative to control alpha-2-macroglobulin. Alpha-2-macroglobulin appears to exist as a simple, slow electrophoretic form in fresh plasma but converts into faster forms upon aging the plasma or during purification. Characterization of the electrophoretic microhetergeneity of alpha-2-macroglobulin preparations should be a prerequisite for the study of its proteinase binding properties.

Cystic fibrosis alpha 2-macroglobulin protease interaction in vitro

alpha 2-Macroglobulin was purified from plasma of five cystic fibrosis patients and five normal controls. SDS gel electrophoresis of native alpha 2-macroglobulin from cystic fibrosis patients and normal donors showed identical subunit molecular weights, as did trypsin cleavage products. Cystic fibrosis and control alpha 2-macroglobulins were indistinguishable by isoelectric focusing and exhibited appropriate shifts in isoelectric point following binding of trypsin. The trypsin-binding capacities of control and cystic fibrosis alpha 2-macroglobulins did not differ, nor did the esterolytic activity of the trypsin-alpha 2-macroglobulin complexes.

Decreased sialic acid and altered binding to lectins of purified alpha 2-macroglobulin from patients with cystic fibrosis

Purified preparations of plasma alpha 2-macroglobulin from patients with cystic fibrosis are shown to have normal amounts of total hexose but as much as 40% decrease in their sialic acid content. The binding of these preparations to concanavalin A and wheat-germ agglutinin was markedly reduced as compared to normal values in controls. Intermediate values were found in obligate heterozygotes. These results suggest a possible alteration in the carbohydrate moiety of alpha 2-macroglobulin in cystic fibrosis, presumably due to a defective posttranslational process.