Abstract
Vitamin B_<12> concentration of healthy human whole blood could be determined utilizing Escherichia coli mutant # 215 as an assay organism. For the purpose of determining the vitamin of blood treated with papain, a modified synthetic medium of Grossowicz et al. brought the satisfactory results. Composition of the medium was based on the formula reported by Johansson, supplemented with 0.25 % of casamino acid treated with hydrogen peroxide to decompose methionine. Vitamin B_<12> concentration of 10 healthy human subjects were determined as described below. (1) In case of the samples pretreated by autoclaving with a KCN solution and an acetate buffer, vitamin B_<12> levels found were 0.269 ± 0.024 mγ/cc and their recovery rates were 87 to 105 %. (2) When the samples were assayed by means of paper bioautography after papain digestion, 0.276 ± 0.028 mγ/cc of vitamin B_<12> was found and the recovery rates were 88 to 110 %. Much higher amount of vitamin B_<12> was found in the serum than in the red cells.
