THE BEHAVIOR OF TRANSFERRIN IRON IN THE RAT

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  • 1 January 1981
    • journal article
    • research article
    • Vol. 57  (2) , 218-228
Abstract
The behavior of rat transferrin was investigated employing acrylamide gel electrophoresis and isoelectric focusing. In vitro labeling with Fe chelates at 30 min was 93-98% effective, whereas binding by simple ferric salts was reduced to 71-76%. Complete and specific binding of 59FeSO4 by the Fe binding sites of transferrin was demonstrated after in vitro or in vivo addition of ferrous ammonium sulfate in pH 2 saline up to the point of Fe saturation. In vitro the radioiron transferrin complex in plasma was stable and its Fe had a negligible exchange with other transferrin binding sites over several hours. The distribution of radioiron added in vitro or through absorption was random between the binding sites of slow and fast transferrin molecule. Fe distribution among body tissues was similar for mono- and diferric transferrin Fe and was unaffected by the site distribution of Fe on the transferrin molecule. The only important aspect of transferrin Fe binding was the more rapid tissue uptake of Fe in the diferric form as compared to monoferric transferrin. Additional in vivo effects on internal Fe exchange were produced by changes in the Fe balance of the animal. In the Fe loaded animal, monoferric transferrin injected into the plasma was rapidly loaded by Fe from tissue and thereby converted to diferric transferrin. Injection of diferric transferrin in the Fe deficient animal was associated with a rapid disappearance from circulation of the original complex and a subsequent appearance of monoferric transferrin as a result of Fe returning from tissues. Plasma Fe apparently behaves as a single pool except that diferric Fe exchange occurs at a more rapid rate than does monoferric Fe exchange.