Transferrins are iron binding transport proteins which can bind two ferric ions in association with the binding of an anion, usually bicarbonate. Lactotransferrin has an antimicrobial activity that depends on the extracelluar cation concentration. The lactotransferrin peptidase S60 domain 1 functions as a serine protease that cleaves arginine-rich regions, contributing to the antimicrobial activity. Lactoferroxins A, B and C contained within lactotransferrin have opioid antagonist activity.