An Apparent Anomaly in the Distribution of Radioiodinated Serum Albumin when added to Red Cell Suspensions

WHEN 15 ml. of suitably diluted (1 in 500) serum albumin tagged with iodine-131 (‘ RISA ’ Abbott) is added to an equal volume of washed human red cells with a volume concentration ρ of about 0.4, and when the red cells are thrown down by centrifuging at 7 × 10 2 g for 15 min., the radioactivity of the supernatant fluid is invariably 10–15 per cent greater than that found in a blank system containing 15 ml. of ‘ RISA ’ plus 15 (1 – ρ) ml. of saline, even after a correction is made for the volume of the blank system being smaller than the volume of the system with which it is compared. If the red cells are first rendered spherical by the addition of 1.5 ml. of a distearyl lecithin sol (5 mgm./5 ml.), the supernatant fluid obtained by centrifuging is 20–25 per cent more radioactive than the supernatant fluid from an appropriately prepared blank.