Vitamin B12-binding Proteins in Normal and Leukemic Human Leukocytes and Sera

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Abstract
The vitamin B12-binding proteins in sera and leukocytes of healthy subjects and patients with chronic myelogenous leukemia (CML) were separated and partially purified by column chromatography as their cyanocobalamin complexes. The molecular weight of transcobalamin I and leukocyte B12-binding protein was 119,000, and that of transcobalamin II was 32,000 as determined by gel filtration. The electrophoretic mobilities were α1 for transcobalamin I, α2 for the leukocyte B12-binding protein, and α2-β for transcobalamin II. After treatment with neuraminidase or chromatographic purification, the mobilities of both transcobalamin I and the leukocyte B12-binding protein became β. Transcobalamin I and the leukocyte B12-binding protein gave a reaction of immunologic identity in immunodiffusion. The fact that leukocytes can produce B12-binding protein in vitro and the similarities between leukocyte B12-binding protein and transcobalamin 1 strongly suggest that CML transcobalamin I is derived from leukocytes.

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