The leishmanicidal flavonols quercetin and quercitrin target Leishmania (Leishmania) amazonensis arginase

► Leishmanicidal flavonoids are strong inhibitors of arginase. ► Quercetin interacts with Mn2+ cofactor and with substrate l-arginine at pH 9.5. ► Catechol group of flavonoids donate two hydrogen bonds to Asp141. ► Quercetin is a mixed inhibitor whereas quercitrin and isoquercitrin are uncompetitive.