Abstract
The tryptophan-niacin conversion ratio was increased by feeding a high-fat diet. One of the most crucial factors determining the rate of metabolic conversion of tryptophan to niacin derivatives was found to be the enzyme activity of α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase [EC 4.1.1.45] (ACMSD) in mammalian liver. Hepatic ACMSD was suppressed by a high-fat diet. We found that only unsaturated fatty acids in the diet possess the ability to reduce ACMSD activity. This phenomenon was observed in hepatocytes in primary culture. We purified ACMSD and cloned the cDNA encoding ACMSD. In rats fed dietary linoleic acid, ACMSD protein and mRNA levels in the liver were strongly suppressed as compared with rats fed a fat-free diet. These results suggest that the transcription level of ACMSD is probably modulated by polyunsaturated fatty acids or their metabolites.
