The interaction of human serum albumin in the native and fully reduced states with apolipoprotein E, serum amyloid protein and very low density lipoproteins from human plasma.

1. Complex formation in a solution of apolipoprotein E (apoE) isolated from human plasma very low density lipoproteins (VLDL) and human serum albumin (HSA) in both native and fully reduced states was studied. The existence of a kinetically unstable complex of apoE and native albumin was shown. The complex became more stable with the reduction of the S--S links in the albumin molecules capable of forming aggregates under these conditions. 2. The interaction between native HSA as opposed to a fully reduced one and isolated VLDL particles was more pronounced, probably, due to the existence of amphipathic alpha-helical regions. 3. Dissociation of the serum amyloid protein (SAP) oligomeric form in solution and the interaction of the protein with fully reduced HSA owing to the provision with the additional hydrophobic surface was shown. ApoE displaced SAP from the complex with fully reduced albumin. 4. It is suggested that the ability of the apolipoprotein to interact with albumin is determined by internal stability of the molecular structure of the latter and the complexes detected in vitro may be a new transport form of apolipoproteins in lipid-free form in serum. It is assumed that competitive interactions in the HSA-SAP-apoE system may be involved in the development of secondary amyloidosis.