Effects of high dietary methionine on activities of selected enzymes in the liver of kittens (Felis domesticus).

1. Growing male kittens were fed an 18% casein diet supplemented with 2, 3, or 4% L-methionine (MET) for 6 weeks. 2. Free MET concentration in liver increased 30-fold and cystathionine two- to three-fold; the activity of adenosyl-MET transferase and cystathionase also increased but remained lower than previously found in rats. 3. Taurine concentration in liver decreased in cats fed excess MET and appeared to depend on taurine intake. 4. Alanine aminotransferase activity was high in all groups while serine dehydratase activity was very low. 5. Pyruvate kinase and malic enzyme activities which are normally low in cat liver increased after excess MET. Also, glucose 6-phosphate and 6-phosphogluconate dehydrogenases increased. 6. Cat liver metabolism showed limited adaptation to an excess dietary intake of methionine compared to that found in rats.