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A Radiometric Microbiologic Assay for the Biologically Active Forms of Niacin

The Johns Hopkins Medical Institutions, Baltimore, Maryland

Correspondence: For reprints contact: Patricia A. McIntyre, The Johns Hopkins Medical Institutions, 615 N. Wolfe St., Baltimore, MD 21205.

ABSTRACT

A radiometric microbiologic assay has been developed for the determination of niacin in biologic fluids. Lactobacillus plantarum produced ¹⁴CO₂ from L-[U-¹⁴C] hr malic acid in quantities proportional to the amount of niacin present. The assay is specific for the biologically active forms of niacin in humans. Thirty normal hemolysates were analyzed and the values ranged from 13.0 to 17.8 µg niacin/ml RBC (mean = 15.27 ± 1.33 s.d.). Good recovery and reproducibility studies were obtained with this assay. On thirty blood samples, correlation was excellent between the radio-metric and the conventional turbidimetric assays.