Bovine apolipoproteins C. I. Isolation and spectroscopic investigations of the phospholipid binding properties.

Seven low-molecular weight proteins of the C class of apolipoproteins have been isolated from bovine serum high density lipoprotein. Amino acid analysis has shown five of these to be equivalent to the apolipoproteins previously described (Lim, C.T. and Scanu, A.M. (1976) Artery 2, 483-496). A spectroscopic examination of these proteins in the presence of increasing amounts of L-alpha-dimyristoyl phosphatidylcholine single-bilayer vesicles indicates that all bovine apolipoproteins C exhibit changes in secondary and tertiary structure as shown by intrinsic fluorescence intensity, wavelength, and polarization changes, and increases in alpha-helical content as seen by circular dichroism. Evidence is presented to show that bovine apolipoproteins C, like all human apolipoproteins of the A and C classes, can cause phospholipid multilamellar liposomes to disrupt and/or rearrange into a smaller complex which scatters less light. This paper details the screening of the bovine apolipoproteins for their phospholipid binding properties, whereas the following paper will examine the nature of their complexes with phospholipid in more detail. Together, these papers represent the first investigation of protein-lipid interactions involving any nonhuman apolipoproteins C.