Some Characteristics of Binding of Vitamin B₁₂ by Normal Human Serum

Serum Protein Binding of Vitamin B1212

“…These results have been confirmed (Beal 1964, Meyer 1965. These same workers demonstrated, from these and later studies (Bertcher et al 1960, Meyer et al 1957 that the binding of vitamin BIZ to human serum proteins in vitro occurs in two phases, an initial phase which is constant for normals but which is increased in most patients with myeloid leukemia and in some patients with polycythemia Vera (Meyer et al 1957; in the second phase of binding, there is less avidity for the vitamin, but the avidity was equal in health and disease. That this increased binding was not due to ionic cobalt resulting from vitamin Bla breakdown was shown by the different results obtained by them with Co6'"C12 in comparison with CoGo-vitamin BIZ.…”

“…It is then assumed that all vitamin BI2 remaining and detectable, by either microbiologic assay or radioactivity counting, within the dialysis bag, is bound to protein. Meyer and his co-workers (Bertcher & Meyer 1957, Bertcher et al 1960, Meyer et al 1957, 1961, added aliquots of from 1.0 to 500 ng of radioactive (Co60) vitamin B12 to the serum samples, and incubated the material in Visking bags at room temperature for two hours; this material was dialysed against cold, running tap water for 48 hours (the commonly used amounts of added vitamin B12 were 1, 2.5, 5 , 10, 25, 50 and 100 ng ml). For purposes of reference these methods have been summarized in Table I.…”

“…Their results have shown higher binding than those determined by microbiologic assay. They showed (Bertcher et al 1960) that it was reasonable to assume that radioactive vitamin BI2 and 'cold' vitamin BIZ were bound by serum proteins in a similar manner. They suggested that the vitamin B12 available for microbiologic assay may not represent the total vitamin bound to serum proteins.…”

Serum Binding of Vitamin B12 Analogues: Identification of Binding Groups in the B12 Molecule*

“…Blz binding is defined as the amount of radio B12 remaining in serum after exhaustive dialysis against running tap water (Bertcher et al, 1960). Radio-vitamins were added at Ievels of I , z ,~, IO,SO and IOO mvg.…”

“…isms (Miller and Sullivan, 1959;Bertcher et al, 1960). Recent studies (Bunge and Schdhg, 1957) have shown that alterations in the porphyrin moiety had no effect, when compared to that of cyanocobalamin.…”