Vitamin B12-binding proteins in the serum of normal subjects and of patients with chronic myelocytic leukemia have been compared. The in-vivo-bound B12 was utilized to identify the binding protein. Column protein chromatography and block and paper electrophoresis were employed individually and in combination to characterize the B12-binding protein.

B12 was found to be bound primarily to an alpha-l globulin in both normal individuals and in patients with chronic myelocytic leukemia. No qualitative difference was found in these proteins.

The increased amounts of B12-binding protein in the serum of patients with chronic myelocytic leukemia would seem to be attributable to abnormal metabolism of the same protein that binds B12 in normal serum.

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