The development of the endoplasmic reticulum of rat hepatocytes was studied during a period of rapid cell differentiation, i.e., from 3 days before to 8 days after birth. Before birth, the ER increases in volume, remaining predominantly rough surfaced; after birth, the increase continues but affects mainly the smooth-surfaced part of the system. These changes are reflected in variations of the RNA/protein and PLP/protein ratios of microsomal fractions: the first decreases, while the second increases, with age. The analysis of microsomal membranes and of microsomal lipids indicates that the PLP/protein ratio, the distribution of phospholipids, and the rate of P32 incorporation into these phospholipids show little variation over the period examined and are comparable to values found in adult liver. Fatty acid composition of total phosphatides undergoes, however, drastic changes after birth. During the period of rapid ER development in vivo incorporation of leucine-C14 and glycerol-C14 into the proteins and lipids of microsomal membranes is higher in the rough-than in the smooth-surfaced microsomes, for the first hours after the injection of the label; later on (∼10 hr) the situation is reversed. These results strongly suggest that new membrane is synthesized in the rough ER and subsequently transferred to the smooth ER.

BIOGENESIS OF ENDOPLASMIC RETICULUM MEMBRANES I. Structural and Chemical Differentiation in Developing Rat Hepatocyte

Chapter iii – lipid peroxidation and fluorescent molecular damage to membranes

(1972). Microsomal Drug Metabolizing Enzymes in Insects. Drug Metabolism Reviews: Vol. 1, No. 1, pp. 153-227.

Microsomal Drug Metabolizing Enzymes in Insects

Biosynthesis of L-ascorbate (vitamin C) occurs by different pathways in plants and mammals. Yeast contain D-erythroascorbate, a C5 analog of ascorbate. UDP-D-glucuronic acid is the precursor in mammals. Loss of UDP forms glucuronic acid/glucuronolactone. Reduction of these at C-1 then forms L-gulonic acid/L-gulono-1,4-lactone. The lactone is oxidized by a microsomal L-gulono-1,4-lactone oxidase to ascorbate. Only the L-gulono-1,4-lactone oxidase has been purified and cloned, and very little is known about the properties of the other enzymes. Plants form ascorbate from GDP-D-mannose via GDP-L-galactose, L-galactose, and L-galactono-1,4-lactone. The final oxidation of L-galactono-1,4-lactone to ascorbate is catalyzed by a mitochondrial L-galactono-1,4-lactone dehydrogenase located on the inner membrane and using cytochrome c as electron acceptor. GDP-mannose pyrophosphorylase and L-galactono-1,4-lactone dehydrogenase have been cloned. Yeast synthesizes D-erythroascorbate from D-arabinose and D-arabinono-1,4-lactone in a pathway analogous to that in plants. The plant, mammalian, and yeast aldonolactone oxidase/dehydrogenases that catalyze the last step in each pathway have significant sequence homology. L-Gulono-1,4-lactone oxidase is mutated and not expressed in animals, such as primates, that have lost ascorbate biosynthesis capacity. Assessment of the literature reveals that little is known about many of the enzymes involved in ascorbate biosynthesis or about the factors controlling flux through the pathways. There is also a possibility that minor alternative pathways exist in plants and mammals.

L-ascorbic acid biosynthesis.

The effect of selenium depletion on mammary tumorigenesis following dimethylbenz[a]anthracene administration was examined in female Sprague-Dawley rats that were fed different levels and types of fats. Four basal diets deficient in selenium were used: (a) 1% corn oil; (b) 5% corn oil; (c) 25% corn oil; and (d) a high saturated fat diet containing 1% corn oil and 24% hydrogenated coconut oil. The comparable selenium-adequate diets were obtained by adding 0.1 ppm of selenium to each of the basal diets. In animals that received an adequate supplement of selenium, an increase in fat intake was accompanied by an increased tumor incidence when corn oil was used in the diets. A high saturated fat ration, on the other hand, was much less effective in this respect. Only in those rats that were maintained on a high polyunsaturated fat diet (25% corn oil) did selenium depletion result in a further increase in tumor incidence and tumor yield. Such an augmentation was not observed in animals given either a 1 or a 5% corn oil ration or a diet rich in saturated fat. Regardless of selenium status, almost all of the tumors formed were adenocarcinomas. An enhancement of tumorigenesis as a result of selenium deficiency in rats fed the 1% corn oil regimen was detected provided a high dose of dimethylbenz[a]anthracene was used, suggesting that alterations in dimethylbenz[a]anthracene metabolism might be involved under this condition. The antioxidant property of selenium is discussed as a possible mechanism by which selenium protects against tumorigenesis, especially in animals with a high polyunsaturated fat intake.

Enhancement of Mammary Tumorigenesis by Dietary Selenium Deficiency in Rats with a High Polyunsaturated Fat Intake

Lipid peroxidation and biosynthesis of l-ascorbic acid in rat liver microsomes

Biosynthesis of L-Ascorbic Acid in Different Sub-Cellular Fractions of Prenatal and Postnatal Rat Livers

Biosynthesis of L-ascorbic acid in different sub-cellular fractions of prenatal and postnatal rat livers.

Biosynthesis of l-ascorbic acid in rat liver microsomes: influences of age, sex, dietary changes, and whole-body x-irradiation.

SummaryDecrease of L-ascorbic acid synthesis by the liver microsomes of C57/BL mice bearing Ehrlich ascites carcinoma for 13 days could be accounted for by decreased food intake of the animals. On the other hand, the decreased ascorbic acid synthesis by liver microsomes from C3H/Crgl mice infected with Gardner lymphosarcoma was due neither to inanition nor to gross infiltration of the liver with tumor cells but to a decrease in the L-gulono dehydrogenase activity. There was no change in the synthesis of ascorbic acid by liver microsomes from C57/ BL mice made immune to Ehrlich ascites carcinoma cells, although the amount of mi-crosomal protein per gram liver was significantly increased. Neither was there a significant inhibition in the synthesis by the liver microsomes of C3H/Crgl bearing T-15 hepa-toma or of A/HC mice bearing L No. 2 lymphoma.

I. B. Chatterjee

Papers

Lipid peroxidation and biosynthesis of l-ascorbic acid in rat liver microsomes

Biosynthesis of L-ascorbic acid in different sub-cellular fractions of prenatal and postnatal rat livers.

Biosynthesis of l-ascorbic acid in rat liver microsomes: influences of age, sex, dietary changes, and whole-body x-irradiation.

Biosynthesis of L-Ascorbic Acid in Liver Microsomes from Mice Bearing Transplanted Tumors∗: