1. Effects of incorporating 30 g leucine/kg into diets on quinolinate phosphoribosyl transferase (QPRT; EC 22.214.171.124) activity and leucine aminotransferase (EC 126.96.36.199) activity were studied in groups of rats receiving 5, 30 and 60 μg of pyridoxine/10 g diet.
2. The results indicated that 30 g leucine/kg diet significantly reduced the QPRT activity when the diets provided 5 μg pyridoxine/10 g and that the effect was only marginal when the diet included 30 μg pyridoxine/ 10 g. The inhibitory effect was completely absent when the diet provided higher amounts of pyridoxine (60 μg/10g).
3. These results suggest that additional amounts of pyridoxine are necessary to counteract the effects of excess of leucine in the diet.
4. Leucine aminotransferase activity was increased in rats given diets containing higher amounts of pyridoxine; supplementary leucine also increased the enzyme activity.