THE PLASMA VITAMIN B12 BINDING SUBSTANCE: I. ITS DETECTION IN THE SEROMUCOID FRACTION OF PLASMA FROM NORMAL SUBJECTS AND PATIENTS WITH CHRONIC MYELO-CYTIC LEUKEMIA *

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Abstract
The fact that intrinsic factor is thought to be a glycoprotein led to an investigation of the B12 content of the seromucoid fraction of plasma. When 0.1 to 1.0 m[mu]g of Co58Bj2Anl was added to plasma from 6 normal subjects and 8 patients with chronic myelocytic leukemia (CML) and free B12 was removed by dialysis, 77 and 83%, respectively, of the bound radioactivity for the 2 groups was found in the seromucoid fraction. When 10 to 100 mug of Co58Bi2/ml was added to plasma from patients with CML an association between the increased binding capacity of this plasma and the increased recovery of radioactivity in the seromucoid fraction was demonstrated. Isolation of the seromucoid fraction indicated that it is not the B12 binding protein. Further purification and chemical analysis of the protein is in progress.