Plasma iron in laying hens is about five times higher
than in non-laying birds and mammals. About half the total iron
has properties different from those of tx'ansferrin-bound iron.
It has been suggested by some workers that the non-transferrin
iron is bound to conalbumin.
In the present work studies were made on plasma
containing the native non-radioactive iron and on plasma to which
radioactive iron Fe) had been added in vivo or in vitro.
Several types of separation techniques (gel filtration on Sephadex,
adsorption on magnesium carbonate, chromatography on DEAE-cellulose)
were employed for the fractionation of the plasma and the
identification of the iron-binding components. Studies were also
made on cockerels where a plasma iron picture similar to that
found normally in laying hens could be induced by the administration
of oestrogen. The results of all these experiments indicate that
the non-transferrin iron is associated with phosphoprotein and
not with conalbumin, although an attempt to isolate Pe-labelled
phosphoprotein quantitatively was only partially successful.
The findings of other workers who have used, various electrophoretic
techniques are discussed and found to be explicable on the basis
of this hypothesis.
Specific radioactivity measurements made after the
incubation of J Pe-transferrin (in normal cockerel plasma) with
the phosphoprotein iron in plasma from laying hens show that
there is no exchange between the two iron fractions in vitro.
Similar measurements made after the intravenous injection of
Fe-transferrin show that in laying hens and oestrogen-treated
cockerels transferrin iron serves as a precursor of the
phosphoprotein iron. Thus the phosphoprotein iron is presumably
derived from transferrin iron in vivo by some process other than
simple transfer in the plasma. It is proposed that the iron
is taken from transferrin by the newly synthesized phosphoprotein
which is leaving the liver cells to be released in the blood
plasma, and that the possible funotion of the phosphoprotein
iron is to serve as a source of iron for the eggs.