Complexing of basic pancreatic proteinase inhibitor with soybean phospholipid multilamellar vesicles

The formation of complexes of basic pancreatic proteinase inhibitor (BPTI) with multilamellar vesicles (MLV) from six preparations of soybean phosphol ipids of various composition was studied. When BPTI, a non-membrane protein , interacts with MLV, the vesicles aggregate, forming a precipitate of prot ein-lipid complexes. The BPTI content in the protein-lipid complexes increa ses with decreasing pH of the medium and on addition of negatively charged components into the lipid mixture. The protein-induced aggregation of the p hospholipid vesicles is suggested to be mainly determined by electrostatic forces. The antiproteinase activity of BPTI in the complexes was rather low but increased up to 70% of the initial activity on addition of an ionic de tergent (sodium deoxycholate).