▁protein ▁mole c ule ▁indicates ▁that ▁the ▁evolution ary ▁development ▁of ▁la ct o fer rin ▁gene ▁occurred ▁by ▁dup lication . ▁Study ▁of ▁polym orphism ▁of ▁gen es ▁that ▁encode ▁la ct o fer rin ▁helps ▁selecting ▁liv est ock ▁bre eds ▁that ▁are ▁resist ant ▁to ▁m ast itis . ▁ ▁M ole cular ▁structure ▁L act o fer rin ▁is ▁one ▁of ▁the ▁transfer rin ▁prote ins ▁that ▁transfer ▁iron ▁to ▁the ▁cells ▁and ▁control ▁the ▁level ▁of ▁free ▁iron ▁in ▁the ▁blood ▁and ▁external ▁secret ions . ▁It ▁is ▁present ▁in ▁the ▁milk ▁of ▁humans ▁and ▁other ▁m amm als , ▁in ▁the ▁blood ▁pl asma ▁and ▁neut roph ils ▁and ▁is ▁one ▁of ▁the ▁major ▁prote ins ▁of ▁virt ually ▁all ▁ex ocr ine ▁secret ions ▁of ▁m amm als , ▁such ▁as ▁sal iva , ▁b ile , ▁tears ▁and ▁pan cre as . ▁Con cent r ation ▁of ▁la ct o fer rin ▁in ▁the ▁milk ▁var ies ▁from ▁ 7 ▁g / L ▁in ▁the ▁col ost rum ▁to ▁ 1 ▁g / L ▁in ▁m ature ▁milk . ▁ ▁X - ray ▁diff raction ▁reve als ▁that ▁la ct o fer rin ▁is ▁based ▁on ▁one ▁pol ype pt ide ▁chain ▁that ▁contains ▁about ▁ 7 0 0 ▁am ino ▁ac ids ▁and ▁forms ▁two ▁hom olog ous ▁glob ular ▁domains ▁named ▁N - and ▁C - lob es . ▁N - lo be ▁corresponds ▁to ▁am ino ▁acid ▁resid ues ▁ 1 –