Human high density lipoprotein, apolipoprotein glutamine II. The immunochemical and lipid binding properties of apolipoprotein glutamine II derivatives

Apolipoprotein glutamine II (apoLP Gln II) is one of the major protein constituents of human plasma high density lipoproteins. The protein is of known amino acid sequence and contains two identical polypeptide chains of 77 amino acids, linked by a single disulfide bridge at residue 6. The authors investigated the effects of chemical modification of this disulfide linkage of the physical, immunological, and lipid binding properties of the protein. The findings show that, while reduction of the disulfide linkage of apoLP Gln II may affect the secondary structure of the protein, this effect is seen only in the absence of lipid. The integrity of the disulfide bond does not appear to be critical for binding of phosphatidylcholine. As assessed by EPR and by fluorescent labels selective for the sulfhydryl group, the environment of apoLP Gln II at or near residue 6 does not appear to be significantly altered by the interaction with and binding of phosphatidylcholine by the protein.