In vitro complex formation between cholesterol and α1‐proteinase inhibitor

Abstract
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.