The in vitro interaction between human (α1-proteinase inhibitor (α1-PI) and cholesterol was studied with electrophoretic and gel Chromatographic methods. The addition of cholesterol (from 1 to 20 mol/mol α1-PI) at 37°C resulted in retarded electrophoretic mobility of α1-PI towards the anode, diminished immunoreactivity and antiproteinase activity. At a molar ratio of 2:1 (cholesterol/α1 -PI), antitryptic activity was reduced by 15% but antielastase activity by 50%. At this ratio the gel filtration α1-PI peak appeared at 67 kDa, as compared to 52 kDa for native α1-pi. No size difference was noted on SDS-PAGE. These results suggest the occurrence of noncovalent complex formation between cholesterol and α1-PI in vitro.
