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 *

Co58B12 ABSORPTION, PLASMA TRANSPORT AND EXCRETION IN PATIENTS WITH MYELOPROLIFERATIVE DISORDERS, SOLID TUMORS AND NON-NEOPLASTIC DISEASES*

“…The absorption in seven subjects with CML in the present study did not differ from this range, nor was the amount absorbed abnormal in the two subjects with myeloid metaplasia and a high serum B12. Heinrich and Erdmann-Oehlecker (12) The data also indicate that the plasma concentration of "unsaturated B12-binding protein" does not greatly influence the amount of B12 absorbed, since plasma from patients with CML has a markedly increased unsaturated B12-binding capacity (13)(14)(15)(16).…”

“…Therefore, the delayed plasma disappearance of the labeled vitamin may merely represent an isotope dilution effect. Since CML plasma has a high unsaturated B19-binding capacity (13)(14)(15)(16), an additional factor may be that as the tracer dose enters the plasma compartment a greater than normal fraction of it is tightly bound to plasma protein.…”

“…In both normal subjects and patients with CML, 80 to 90 per cent of total plasma B12 is tightly bound to an a1-globulin present in the seromucoid fraction of plasma (16). Since, within a few hours following an oral dose of Co58B12, the radioactive By2 appearing in plasma is also in this form (13) it seems reasonable to assume that, once absorbed, an orally administered dose of Co58B12 rapidly equilibrates with the total plasma B12.…”

Serum Protein Binding of Vitamin B1212

“…Weinstein & Watkin (1960) studied the absorption of ingested radioactive vitamin Blz in patients with hematologic disorders. As corollaries, Weinstein & Watkin (1960) suggested that the serum vitamin B,, concentration does not control the amount of vitamin BI2 absorbed, and further, that the increase of serum concentration of unsaturated vitamin Bla binding proteins did not influence the amount of vitamin Blz absorbed, since the binding capacity of serum from chronic myeloid leukemic patients was markedly increased (Pitney et al 1954, Weinstein et al 1959. As corollaries, Weinstein & Watkin (1960) suggested that the serum vitamin B,, concentration does not control the amount of vitamin BI2 absorbed, and further, that the increase of serum concentration of unsaturated vitamin Bla binding proteins did not influence the amount of vitamin Blz absorbed, since the binding capacity of serum from chronic myeloid leukemic patients was markedly increased (Pitney et al 1954, Weinstein et al 1959.…”

Characteristics of Vitamin B_I2 Binding by Erythrocytes and their Components

“…W einstein (8) demonstrated that plasma B12 binding factor is included in seromucoid, which he defined as the phosphotungstic acid precipitate of a perchloric acid filtrate of plasma. We applied the same method to a stroma-B12 complex formed by adding 25 m^g.…”