Subject: Questions about transferrin

Question 1: Why is there a color change when ferric iron is added to transferrin?
I have read a few articles that state that there is a colour change when ferric
iron (fe3+) is added to transferrin resulting in an absorbance maxima at 465nm.
However they state that there is no colour change when ferrous iron (fe2+)is
added. I was wondering why this is? 

Question 2: How do you determine if carbonate or bicarbonate is bound to transferrin?
I have read a few articles that state that carbonate is bound to transferrin and
others that state it is bicarbonate. How do you determine which it is or does it
make a difference and I am being picky about somethin

Re: Questions about transferrin