The interaction of transferrin with isolated hepatocytes.

Freshly isolated rat hepatocytes display abut 36700 high-affinity sites to which differic transferrin may bind with an apparent association constant of 1.62 . 10(7) l . mol-1. Uptake of iron from diferic transferrin by hepatocytes is linear with time and is accelerated at increased diferric transferrin concentrations. Apotransferrin is able to decrease net iron uptake by hepatocytes from diferric transferrin by a process not dependent on the apotransferrin concentrations used or on the rate at which the cells take up iron. Immunoprecipitation of the apotransferrin during these incubations indicate that iron is being released from the cells to apotransferrin at the same time as iron is being taken up from diferric transferrin. The simultaneous uptake and release of iron, and the insensitivity to apotransferrin concentration, suggest that the processes of iron uptake and release occur via separate mechanisms. The effect of apotransferrin on net retention of iron may be one way in which the in vivo distribution of iron between sites of storage and utilization is controlled.