1. Preparations of bound nicotinic acid obtained from wheat bran by an acid extraction procedure (‘niacytin preparations’) were resolved into several nicotinic acid-containing components.
2. Extraction of wheat bran under neutral conditions yielded 62% of the bound nicotinic acid in solution; of this 90% was non-diffusible. Methods were developed which gave high yields of ‘non-diffusible nicotinic acid’ preparations.
3. The bound nicotinic acid in the latter preparation was linked to macromolecules of mol. wt about 1500 to 17000 daltons, approximately 60% of which were polysaccharide and 40% peptide or glycopeptide in character.
4. o-Aminophenol, and ferulic and sinapic acids, are also contained in macromolecules in wheat bran, but are not directly associated with the bound nicotinic acid.
5. The significance of these results in explaining the nutritional unavailability of bound nicotinic acid is discussed.