Études sur la structure de l'α2 macroglobuline humaine I. Préparation de l'α2 macroglobuline humaine

Subunit structure of human alpha 2-macroglobulin (alpha 2-MG) with respect to its interaction with trypsin

SDS-polyacrylamide gel electrophoresis of a recently prepared alpha 2-macroglobulin solution showed only the polypeptide chains of 190,000 molecular weight. Reduction-alkylation of this preparation followed by gel-filtration on a Sephadex G-200 column in 5.2 M guanidine hydrochloride was unable to separate a fraction of 83,000 molecular weight as previously described. Nevertheless, after incubation of a mixture alpha 2-macroglobulin-trypsin during 45 minutes at 37 degrees C, approximately 60 per cent of the preparation were converted in a component with 83,000 molecular weight as detected in SDS polyacrylamide gel. That component was isolated on Sephadex G-200 in guanidine hydrochloride and corresponds to the subunit, fraction II. According to the results of the present work together with those of previous studies, it can be assumed that alpha 2-MG is a 780,000 molecular weight protein (19S) formed of two half-molecules of equal weight (11-12S). The half-molecule contains two polypeptide chains of 180,000-190,000 molecular weight, each of them having, in its middle, a specific region particularly susceptible to attack by proteases.

Purification of alpha 2-macroglobulin with trypsin-like activity from pleural fluids

An alpha 2-macroglobulin with trypsin-like activity has been purified from pleural fluids of patients suffering from chronic pancreatitis. The isolation procedure includes ammonium sulphate precipitation, gel-filtration on Sephadex G-200 and DEAE-cellulose chromatography. It gives 46-fold purification of alpha 2-macroglobulin with a 13% recovery. Based on titration experiments with pancreatic inhibitor, the protein from three different patients contained 0.28, 0.46 and 0.80 mol of trypsin-like protease per mol of alpha 2-macroglobulin.

Generation of an esterolytic and kinin-forming kallikrein-alpha2-macroglobulin complex in human serum by treatment with acetone

Kinin-forming and esterolytic activity in human citrate plasma has been activated by treatment of the plasma with acetone. By far most of the esterolytic activity if not all of it was recovered in an alpha2-macroglobulin (alpha2M) kallikrein complex (SI) which was characterized and purified by chromatography. Little if any esterolytic activity was present which could be ascribed to free plasma kallikrein. The alpha2M-kallikrein complex had kinin-releasing activity though much less than free plasma kallikrein, relative to esterolytic potency. This explains that a considerable fraction of the kinin-forming potential of acetone-activated plasma resides in free plasma kallikrein although it represents only a very small portion of the total kallikrein store. Like free plasma kallikrein the alpha2M complex releases kinin from LMW-kininogen less efficiently than from HMW, in systems of purified components. In whole plasma, the efficiencies change: whereas plasma kallikrein is rapidly inactivated by endogenous inhibitors, the alpha2M complex is protected from further inactivation and capable of releasing kinin continuously if slowly, attacking also LMW-kininogen after HMW-kininogen has been consumed by free kallikrein. While the alpha2M-complex in this respect differs functionally from free plasma kallikrein and explains earlier observations suggesting the presence of two kininogenases, it seems doubtful now that two truly different kininogenases exist in human plasma. The results suggest that acetone predominantly inactivates full inhibitors of kallikrein such as C1INH whereas alpha2M is somewhat more resistant and (pre-)-kallikrein even more. Depending on the time and temperature of acetone treatment one obtains more or less total kallikrein and varying proportions of free to bound enzymes. It is likely that acetone does not turly trigger an activation of prekallikrein but supports spontaneous activation by slowing down the control of the feedback reinforcement of this activation, by damaging inhibitors.