A Vitamin B₁₂‐binding Factor Formed in Cultures of Euglena gracilis var. bacillaris

Summary. Supernatants from centrifuged cultures of the vitamin B 12 ‐requiring alga, Euglena gracilis var. bacillary , contain a ther‐molabile factor, which combines with the vitamin. The complex of vitamin B 12 , and the “Euglena factor” thus formed cannot be taken up by the wild‐type E. coli E 35 and is non‐dialyzable through cellophane. The amount of the factor in the Euglena supernatants increases with the age of the Euglena cultures and is probably an excretion product of the Euglena cells. The factor, as regards its B 12 ,‐binding effect, its thermo ability, and its non‐dialyzability, resembles preparations of the “intrinsic factor of C astle .