VITAMINS

ADP-ribosylation is a group of posttranslational modifications of proteins that have regulatory functions in the cell. In particular, poly(ADP-ribosyl) action or poly (ADP-ribose) synthesized on protein proved to play important roles in DNA repair, carcinogenesis, cell differentiation, and cell cycle events. Recent progress in the research of this variety of biological roles is reviewed on the basis of structure and function of poly (ADP-ribose) synthetase as revealed by molecular cloning techniques and by use of specific inhibitors.

View full abstract

Show abstractHide abstract

Regulation of squalene epoxidase in the cholesterol biosynthetic pathway was studied in human hepatoma cell line, Hep G2 and in rat liver. Incubation of Hep G2 cells with L-654, 969, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, increased squalene epoxidase activity, whereas low-density-lipoprotein (LDL) decreased it. In rat liver microsomes, cholestyramine feeding and the administration of reductase inhibitor to rats increased the epoxidase activity. Cholesterol feeding reduced it. These results demonstrate that squalene epoxidase is regulated by endogenous and exogenous sterols in Hep G2 cells and in rat liver. NB-598, a specific inhibitor of mammalian squalene epoxidase, was used to investigate the regulatory mechanism of cholesterol metabolism in Hep G2 cells. The inducibility by NB-598 in HMG-CoA reductase activity was rather low as compared to that by L-654, 969, though NB-598 inhibited cholesterol synthesis more potently than L-654, 969. On the other hand, the reductase mRNA was increased to the same extent. Therefore, NB-598 is thought to have no effect on the synthesis of nonsterol suppressor derived from mevalonate. NB-598 strongly increased LDL receptor activity. These observations indicate that squalene epoxidase inhibitor is expected to be highly effective in the treatment of hypercholesterolemia.

View full abstract

Download PDF (1662K)

Effect of dietary corn oil content on the urinary excretion ratio of (N^-methyl-2-pyridone-5^carboxamide + N^1-methyl-4-pyridone-3-carboxamide)/N^1-methylnicotinamide was investigated using rats. The male rats of the Wistar strain (3 weeks old) were fed on a 20% casein -0% corn oil, 20% casein - 5% corn oil (control) or 20% casein - 20% corn oil diet ad libitum for 41 days and the rats were then killed by decapitation. Urine samples were collected periodically. The excretion ratio was always statistically significantly higher in the 5% corn oil group than in the 0% and 20% corn oil groups and the liver N^1-methyl-4-pyridone-3-carboxamide-forming N^1-methylnicotinamide oxidase activity, which affects the excretion ratio, was statistically significantly higher in the 5% oil group than in the 0% and 20% oil groups. Accordingly, it was found that low of high dietary oil content lowers the excretion ratio of N^1-methyl-2-pyridone-5-carboxamide + N^1-methyl-4-pyridone-3-carboxamide)/ N^1-methylnicotinamide.

View full abstract

Vitamin B_1 contents in foods are determined by the thiochrome flurometric method (method 1) and high performance liquid chromatography with the post-column derivatization using potassium ferricyanide (method 2). In all foods studied, vitamin B_1 content determined by the method 1 agreed with the sum of 2-(1-hydroxyethyl) thiamin and thiamin contents determined by the method 2 (correlation coefficient=0.9996, n=43). 2-(1-hydroxyethyl)thiamin was newly found in dried purple laver, parsley, fish roe and Nameko. The contents of 2-(1-hydroxyethyl) thiamin and thiamin in pork, inside ham were recognized to be no change at +5℃ and -15℃ for 10 days. The destruction degree by heat depended on temperature and pH, and 2-(1-hydroxyethyl) thiamin was more sensitive to those factors than thiamin. It was found that a part of 2-(1-hydroxyethyl) thiamin was converted to thiamin by heat treatment.

View full abstract

Register with J-STAGE for free!