Radioisotopic assay of vitamin B 12.

Coated charcoal assay of erythrocyte vitamin B 12 levels.

Diagnosing vitamin B-12 deficiency on the basis of serum B-12 assay.

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Vitamin B-12.

V itamin B-12 is a cofactor for 2 enzymes. In the cytoplasm, methionine synthase requires vitamin B-12 in the form of methylcobalamin and catalyzes the conversion of homocysteine to methi-onine by transfer of a methyl group from methyltet-rahydrofolate. This enzyme links the methylation pathway through synthesis of the methyl donor S-adenosyl methionine and the pathway in which purine and pyrim...

Practice Lesson of the week Diagnosing vitamin B-12 deficiency on the basis of serum B-12 assay

Serum vitamin B-12 concentrations are measured to assess the presence of its deficiency in patients presenting with haematolological, neurological, and neuropsychiatric abnormalities. Replacement therapy is instituted promptly, particularly to prevent irreversible neurological and cognitive dysfunction. I present two cases with paradoxical vitamin B-12 results, which highlight the fallacies of ...

The Vitamin B 12 Coenzyme

INTRODUCTION In 19'58 Barker and his associates l 3 recognized a new coenzyme which controlled the conversion of glutamate into ,8-methylaspartate by Clostridium tetanomorph'im. The coenzyme was shown4 to be related to ",-vitamin B12, i.e. contair ing an adenine nucleotide grouping in place of the 5,6-dimethylbe:nziminalole nucleotide of vitamin B12, although similar coenzymes containing b{ nzi...