Circular dichroism studies on the effects of ethanol on the conformation of alpha1-acid glycoprotein, alpha1-antitrypsin, deoxyribonuclease, pepsinogen, soybean trypsin inhibitor and unfolded ribonucleases.

The effects of 25 to 75 volume-% ethanol on conformation of human serum alpha1-acid glycoprotein, human serum alpha1-antitrypsin, pancreatic deoxyribonuclease I, porcine pepsinogen, the "Kunitz" trypsin inhibitor from soybeans, and oxidized as well as reduced and S-carboxymethylated ribonucleases were tested by the circular dichroism (CD) probe. It was found that 25 volume-% ethanol had a slight effect, whereas 50--75 vol.-% alcohol significantly altered the conformation. The tertiary structure was perturbed and the polypeptide main chain was reorganized into new conformations of higher helix and beta-structure contents than in the native state. Comparison of the various proteins showed that the degree of reorganization depended chiefly on the cross-linking of the main chain by disulfide bridges. While the unfolded ribonucleases were refolded by 25 vol.-% ethanol into ordered conformations, the native ribonuclease and alpha1-antitrypsin was more sensitive to 25 vol.-% ethanol than the conformation of alpha1-acid glycoprotein, pepsinogen, and soybean trypsin inhibitor. Almost complete restoration of the native conformation was achieved by diluting the alcohol-containing solutions with water or by dialysis against water or buffer solutions. However, the renaturation depended on the time of contact with alcohol and on the temperature at which the alcohol-containing solutions were kept.     

Acute phase protein alpha 1-acid glycoprotein interacts with plasminogen activator inhibitor type 1 and stabilizes its inhibitory activity.

alpha(1)-Acid glycoprotein, one of the major acute phase proteins, was found to interact with plasminogen activator inhibitor type 1 (PAI-1) and to stabilize its inhibitory activity toward plasminogen activators. This conclusion is based on the following observations: (a) alpha(1)-acid glycoprotein was identified to bind PAI-1 by a yeast two-hybrid system. Three of 10 positive clones identified by this method to interact with PAI-1 contained almost the entire sequence of alpha(1)-acid glycoprotein; (b) this protein formed complexes with PAI-1 that could be immunoprecipitated from both the incubation mixtures and blood plasma by specific antibodies to either PAI-1 or alpha(1)-acid glycoprotein. Such complexes could be also detected by a solid phase binding assay; and (c) the real-time bimolecular interactions monitored by surface plasmon resonance indicated that the complex of alpha(1)-acid glycoprotein with PAI-1 is less stable than that formed by vitronectin with PAI-1, but in both cases, the apparent K(D) values were in the range of strong interactions (4.51 + 1.33 and 0.58 + 0.07 nm, respectively). The on rate for binding of PAI-1 to alpha(1)-glycoprotein or vitronectin differed by 2-fold, indicating much faster complex formation by vitronectin than by alpha(1)-acid glycoprotein. On the other hand, dissociation of PAI-1 bound to vitronectin was much slower than that from the alpha(1)-acid glycoprotein, as indicated by 4-fold lower k(off) values. Furthermore, the PAI-1 activity toward urokinase-type plasminogen activator and tissue-type plasminogen activator was significantly prolonged in the presence of alpha(1)-acid glycoprotein. These observations suggest that the complex of PAI-1 with alpha(1)-acid glycoprotein can play a role as an alternative reservoir of the physiologically active form of the inhibitor, particularly during inflammation or other acute phase reactions.