High performance liquid chromatography and time-of-flight secondary ion mass spectrometry: a new dimension in structural analysis of apolipoproteins.

We report the isolation and characterization of an apolipoprotein A-I mutant using a new technique for structural analysis of apolipoproteins based upon the combined techniques of protein isolation by isoelectric focusing in immobilized pH-gradients, reversed-phase HPLC of tryptic peptides, and subsequent molecular weight analysis of isolated peptides by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The particular advantages of the TOF-SIMS procedure in the characterization of proteolytic peptides are the detection limits in the picomole range, the accuracy of molecular weight determination (up to 3000 +/- 1 D), the speed of analysis, and the wide range of applications for involatile biomolecules. The described procedure for the analysis of apolipoproteins requires only 2 ml of serum as starting material. This method can be used to monitor for genetic polymorphisms and posttranslational modifications on a microscale basis. Applying these techniques, we characterized a new apolipoprotein A-I mutant with an amino acid exchange arginine177 by histidine.