3 3 3 ▁and ▁C - lo be ▁to ▁ 3 4 5 – 6 9 2 , ▁and ▁the ▁ends ▁of ▁those ▁domains ▁are ▁connected ▁by ▁a ▁short ▁α - hel ix . ▁Each ▁lo be ▁consists ▁of ▁two ▁sub dom ains , ▁N 1 , ▁N 2 ▁and ▁C 1 , ▁C 2 , ▁and ▁contains ▁one ▁iron ▁binding ▁site ▁and ▁one ▁g ly cos yl ation ▁site . ▁The ▁degree ▁of ▁g ly cos yl ation ▁of ▁the ▁protein ▁may ▁be ▁different ▁and ▁therefore ▁the ▁mole cular ▁weight ▁of ▁la ct o fer rin ▁var ies ▁between ▁ 7 6 ▁and ▁ 8 0 ▁k Da . ▁The ▁stability ▁of ▁la ct o fer rin ▁has ▁been ▁associated ▁with ▁the ▁high ▁g ly cos yl ation ▁degree . ▁ ▁L act o fer rin ▁belongs ▁to ▁the ▁basic ▁prote ins , ▁its ▁is oe lect ric ▁point ▁is ▁ 8 . 7 . ▁It ▁exists ▁in ▁two ▁forms : ▁iron - rich ▁hol ol act o fer rin ▁and ▁iron - free ▁ap ol act o fer rin . ▁Their ▁t ert i ary ▁structures ▁are ▁different ; ▁ap ol act o fer rin ▁is ▁character ized ▁by ▁" open " ▁con formation ▁of ▁the ▁N - lo be ▁and ▁the ▁" closed " ▁con formation ▁of ▁the ▁C - lo be , ▁and ▁both ▁lo bes ▁are ▁closed ▁in ▁the ▁hol ol act o fer rin . ▁ ▁Each ▁la ct o fer rin ▁mole c ule ▁can ▁revers