CD13 is necessary for the efficient restoration of membrane organization. (A) HUVECs were analyzed for distribution of the marker protein flotillin-1 under conditions that inhibit filopodia formation. Control HUVECs (control) indicate normal flotillin-1 distribution. Sonicated cell lysates containing equivalent total protein levels from trypsinized HUVECs were plated in noncoated plastic dishes and rocked in serum-containing medium (nonadherent), plated in serum-containing medium in tissue culture–coated dishes in the absence (recovered), or the presence of bestatin (recovered + bestatin; 100 μg/mL) were analyzed by sucrose gradient separation and fractions assayed for flotillin-1 by Western blot analysis. Heavy fractions (fractions 1-5) represent higher-density protein complexes, whereas light fractions (fractions 9-12) contain proteins complexed with lipids, such as lipid rafts/caveolae. Results are representative of 3 separate experiments. (B) The relative distribution of flotillin-1 in light versus heavy sucrose gradient fractions in cells “recovered” in the presence of bestatin versus control vehicle was calculated using densitometric quantification of Western blots. The overall distribution of flotillin-1 in the gradient fractions was significantly different between the 2 conditions (P < .02). Data are shown as means (± SD, n = 3).