The Form of Combination of Radioactive Iron and Copper in Plasma Following Ingestion

It has been generally accepted as a fact that iron in transport in the blood plasma following its ingestion occurs in combination with globulin. The use of radioactive isotopes enables us to distinguish between iron† and copper‡ normally found and that recently added to the body economy. In earlier experiments we reported that, whereas about 80% of the radio iron in plasma shortly after feeding was in the filtrate following precipitation of the proteins by trichlor-acetic acid, nearly all of the iron in the red cell was in a form which was precipitated with this acid. 1 Below we tabulate further data relating to this subject.

It can be seen that in a longer series of observations the fraction of iron in the plasma which is not precipitated by trichloracetic acid constitutes about 90% of the total iron (Table I) under the conditions of these experiments. Furthermore, the time after ingestion does not seem to be related to the amount of iron found in this fraction.

In Table II are listed the results obtained in an extension of these observations. By various procedures, the amount of iron in combination with protein was determined and found to be about 95% of the total. However, only about 15% of the iron was found to be actually bound to globulin as determined by half-saturation with ammonium sulphate.