抄録
The effects of dietary protein on the ornithine decarboxylase (ODC) activity in rat liver were investigated, using whole egg protein, casein, gluten, and zein as the protein sources. In short-term feeding (fast-refed), ODC was induced in response to the nutritive value of dietary protein. In long-term feeding (2 weeks), however, ODC was induced by only the zein diet. At the same time, both the ornithine carbamoyltransferase (OCT) and ornithine-oxo-acid aminotransferase (OAT) activities were markedly decreased. OCT and OAT were specifically inhibited by leucine in vitro. ODC was also induced by an amino acid mixture simulating zein (A-l). Moreover, ODC was decreased by the diet (A-2) in which leucine was reduced from A-l, and was increased by the diet in which ornithine was added to A-2. These results suggest that the induction of ODC by feeding the zein diet for 2 weeks is due to the increased concentration of ornithine, arising mainly from the inhibition of OCT and OAT by leucine, which is contained in a large quantity in zein.
