Separation of An. quadrimaculatus aminopeptidase N from solubilized BBMV proteins by anion-exchange chromatography. The UV absorbance at 280 nm (mAU) is indicated at the top left corner, and the percent conductivity of buffer B (%) is indicated at the top right corner. Collected fractions are shown at the bottom in 2-ml intervals. Run volume is indicated at the bottom (ml). Fractions 19–21 and 24–34 contain APN activity.