A. High dose MPO modification, at an H2O2:apoAI mole ratio of 15:1, was performed on rh-apoAI, rh-apoAI 3MV (3 internal Met substituted with Val), and rh-apoAI 3MV treated with formic acid (rh-apoAI 3MV F.A.), which deletes the initiation Met and 6-His tag. Cellular cholesterol efflux activity was determined as the Methods section. Data are mean ± S.D. of duplicate determinations. B. rh-ApoAI (filled circles, solid line) and rh-apoAI 3MV (open circles, dashed line) were subjected to modification by MPO at varying H2O2: apoAI mole ratios. These proteins were then assayed for ABCA1 dependent cellular cholesterol acceptor activity as described in Fig. 3. Data are means ± S.D. of triplicate determinations. *, p<0.01 vs. rh-apoAI 3MV at the same H2O2: apoAI mole ratio, by two tailed t-test.