Note on New Procedure for Isolating Ferritin from Horse Liver

In the previous paper (1) a procedure was outlined for the isolation of a highly purified, apparently crystalline, blue-green colored copper protein from horse liver. The precipitate obtained in step 8 of the isolation procedure (1), contains a number of proteins of potential biochemical interest. Two of these proteins, in addition to the copper protein, have been separated by fractionation with ammonium sulfate. One of these is ferritin, 1 which was isolated as follows: (a) The protein precipitate from step 8 (1), was dissolved in water, the pa adjusted to 7.0, and the mixture centrifuged and any residue discarded. (b) Saturated ammonium sulfate (70 gm./100 ml.) was added to give a 47.5 per cent saturation. The pH was then determined and adjusted to 6.8. A brick red colored precipitate was obtained. (c) The precipitate was packed down by centrifugation and the supernatant liquid carefully decanted off. I t was then taken up in H20 and dialyzed in the cold room against running distilled H20 for 48 hours. Any sediment present was removed by centrifugation. The clear red fluid thus obtained gave a positive precipitin test for ferritin (2). 2 (d) Crystallization of the ferritin from this solution was secured by adding ~ volume of 20 per cent cadmium sulfate (3 Cd SO4-8H20) according to the procedure of Laufberger (3). The crystals begin to form in a few hours, and a considerable crop can be isolated by centrifugation after 24 hours' standing. The crystal form is shown in Fig. 1. They are octahedral in shape, most of them being twinned. The crystals