FIGURE 4.

Mass spectrometric analysis and the ratio of mature to pro-apoA-I in HDL from PCPE2^−/− mouse plasma. A and B, molecular masses of HDL apoA-I after maximum entropy transformation of the electrospray spectrum of FPLC purified HDL apoA-I from chow-fed C57BL/6 mice (A) and PCPE2^−/− mice (B). The most abundant mass in each spectrum was identical within the ±1.4 Da S.D. to the mass of mature mouse apoA-I at 27,950 Da. The minor spectrum peak is consistent with the mass of mouse pro-apoA-I at 28,815 Da. C and D, the relative intensity of apoA-I tryptic peptides from LC-MS/MS analysis. ApoA-I from whole mouse plasma was separated by 12% SDS-PAGE followed by in-gel trypsin digest and then analyzed for the N-terminal tryptic pro-apoA-I peptide and mature apoA-I peptide: C57BL/6 mouse plasma (C) and PCPE2^−/− mouse plasma (D) as described under “Experimental Procedures.” Peptides were separated by reverse-phase HPLC and analyzed for tryptic peptide of the N-terminal T1 for mature peptide (m/z 1132.48) and the T1 propeptide (m/z 1995.88), shown in selective ion chromatograms. The mature murine T1 tryptic peptide has the amino acid sequence DEPQSQWDK, and the unprocessed pro-form has the sequence WHVWQQDEPQSQWDK.