INVITRO COMPLEX-FORMATION BETWEEN CHOLESTEROL AND ALPHA-1-PROTEINASE INHIBITOR

The in vitro interaction between human alpha1-proteinase inhibitor (alpha1-PI) and cholesterol was studied with electrophoretic and gel chromatographic methods. The addition of cholesterol (from 1 to 20 mol/mol alpha1-PI) at 37-degrees-C resulted in retarded electrophoretic mobility of alpha1-PI towards the anode, diminished immunoreactivity and antiproteinase activity. At a molar ratio of 2:1 (cholesterol/alpha1-PI), antitryptic activity was reduced by 15% but antielastase activity by 50%. At this ratio the gel filtration alpha1-PI peak appeared at 67 kDa, as compared to 52 kDa for native alpha1-PI. No size difference was noted on SDS-PAGE. These results suggest the occurrence of noncovalent complex formation between cholesterol and alpha1-PI in vitro.