SUMMARY
1. Ten analogues of vitamin B12 have been tested
for vitamin B12 activity in chick growth.
2. The only naturally occurring analogue to show
activity was the 5-hydroxybenziminazole derivative
(vitamin B12111), which had 4-5 % of the activity
of vitamin B12
3. Four analogues containing benziminazole in
the nucleotide also had vitamin B12 activity; they
were the analogues with benziminazole (23 %),
monomethylbenziminazole (35-41 %), dichloro-
benziminazole and naphthiminazole (the last two
almost as active as vitamin B12 itself).
4. Pseudovitamin B12 and factor B in large
doses by mouth, but not by injection, reduced the
effect of vitamin B12 given simultaneously. In a
single test factor D showed similar antagonism when
given by mouth or by injection.
5. Factor A and the diaminopurine derivative
were inactive, but not antagonistic to vitamin B12.
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