Effect of 6-aminonicotinamide on pentose cycle activity in isolated hepatocytes.

1. 6-aminonicotinamide (6AN), a purported inhibitor of 6-phosphogluconate (6PG) dehydrogenase, has been regarded as an inhibitor of the pentose cycle. 2. Incubation of isolated hepatocytes with 6AN caused a time- and concentration-dependent accumulation of 6PG. 3. At 5 mM, 6AN increased the 6PG level 1000-times to values comparable to those observed in the livers of rats injected with this niacin antagonist. 4. Despite the accumulation of 6PG, neither the total rate of lipogenesis, nor the incorporation of radioactivity from [3-3H]glucose, used to estimate the activity of the pentose cycle, were impaired to a large extent. 5. The evidence presented suggests that the accumulation of 6PG is not a sufficient criterion to establish blockade of the pentose cycle.