The Metabolism in Man of Intravenously Injected Iodine-Labelled Transcobalamin I Not Saturated with Cobalamin

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Abstract
Gimsing, P. & Nexö, E. The Metabolism in Man of Intravenously Injected Iodine-Labelled Transcobalamin I Not Saturated with Cobalamin. Scand. J. clin. Lab. Invest. 36, 669–672, 1976. Transcobalamin I not saturated with cobalamin was purified. After iodine-labelling, a fraction of approximately 0.6 retained its cobalamin-binding capacity. Iodinated protein was used for turnover studies in three healthy subjects. The plasma curves obtained were identical to those of iodinated transcobalamin I saturated with cyanocobalamin. The cobalamin-binding capacity of the iodinated protein was determined on microcolumns containing insolubilized cobalamin. The binding capacity decreased rapidly, only 50% of the initial unsaturated cobalamin-binding capacity remaining after 0.2 to 0.3 days. It is concluded that the turnover of transcobalamin I not saturated with cobalamin does not differ from the turnover of transcobalamin I saturated with cyanocobalamin, and that transcobalamin I saturated with cobalamin in vivo is metabolized at the same rate as is transcobalamin I saturated with cyanocobalamin in vitro.