BINDING AND IRON DELIVERING OF OVOTRANSFERRIN TO CHOLESTEROL-DEPLETEDCHICK-EMBRYO RED-BLOOD-CELLS

Binding and iron delivering of ovotransferrin (OTf) were evaluated usi ng 14-day old chick-embryo red blood cells (CERBC) and cholesterol-dep leted by treatment with chicken egg phosphatidyl choline (E-PC) liposo mes. Liposome-treated CERBC assayed for their cholesterol content show ed a cholesterol depletion depending on the incubation time, being 25% (w/w) of the maximum cellular removal of cholesterol seen after 22 h incubation at 37 degrees C. Total phosphorus content did not change ei ther for the various samples or during the different incubation times, indicating that specific cholesterol removal occurred, as confirmed a lso by the increased membrane fluidity revealed through fluorescence a nisotropy measurements. The apparent dissociation constant (K-d) of co ntrol and treated CERBC was almost of the same value at the same incub ation time, ranging from 0.30 mu M after 0.25 h incubation to 0.19 mu M after 14 or 22 h incubation. In all experiments, the maximum value o f bound OTf molecules per cell (B-max) notably decreased as incubation time increased. But, in cholesterol partly depleted CERBC, the decrea se of the B-max values was less pronounced as the incubation time incr eased. As far as binding experiments were concerned, iron uptake studi es showed that uptaking capacities decreased as incubation time increa sed. Considering both binding and iron uptake, at the same incubation time, liposome-treated CERBC were slightly more efficient with respect to untreated samples. In any case a passive iron delivering could be evidenced after 22 h incubation. It is suggested that cholesterol may tune binding and iron uptake by either regulating or affecting the exp ression or mobility of the OTf receptor.