Amphiphilic properties of the low molecular weight component of serum amyloid-A protein shown by charge-shift electrophoresis.

To test whether the low molecular weight component of serum amyloid-A protein (SAAL) is amphiphilic in character, serum amyloid-A protein (SAA)-containing sera and isolated SAAL were subjected to charge-shift electrophoresis by the technique of Helenius and Simons (Helenius, a. and Simons, K. (1977) Proc. Natl. Acad. Aci. U.S.A. 74, 529-532). When compared to six hydrophilic and two amphiphilic serum proteins, SAAL was shown to behave like the latter in this test. Therefore, SAAL displays properties of apolipoproteins and integral membrane proteins. In the same test, amyloid-A protein (AA) also was found to be amphiphilic, confirming a previous report. The fact that protein AA displays a larger charge shift than that of protein SAAL suggests that the main hydrophobic site of SAAL resides in its N-terminal AA-portion rather than in its C-terminal (SL) part.