Abstract
1. When human serum is heated at 100° at pH 7.4, 6.8 or 4.6, dissociation of the bound form of vitamin B12 occurs most rapidly at pH 4.6. The addition of a minute quantity of cyanide promotes the dissociation. No difference was found among the three pH levels when heated for 30 minutes and the addition of cyanide in this case had no effect.
2. When heated at pH 6.8 for 30 minutes and the dissociation of the bound form at 100° is taken as 100per cent, dissociation is 0per cent at 50°, 5per cent at 60°, 20per cent at 70°, 50per cent at 80° and 85per cent at 90°.
3. The bound form is dissociated almost 100per cent when it is allowed to react with trypsin for 2 hours and about 75per cent with pepsin.
4. Change in the binding capacity of the vitamin B12-binding protein in α-globulin fraction of serum by treatment with oxidizing agents and other chemicals was examined by two different methods. It was found that the binding capacity was almost completely destroyed by periodate. From this finding the vitamin-B12-binding protein in α-globulin fraction was assumed to be a kind of glycoprotein.
