Protein composition of liver nuclear ribonucleoprotein particles of rats fed carcinogenic aminoazo dyes

The feeding of carcinogenic 3′-methyl-4-dimethylaminoazobenzene to rats alters the protein composition of liver nuclear 30S ribonucleoprotein particles which are proposed to be involved in the processing and transport of the newly synthesized RNA. After 10 weeks of feeding of the carcinogenic aminoazo dye, one of the major proteins is missing from these particles but not from the particles isolated from liver of animals fed with noncarcinogenic 4-aminoazobenzene. In all the groups of rats studied, the RNA associated with the isolated particles was of high specific activity.     

Gluconeogenesis by parenchymal cells isolated from livers of carbon tetrachloride-treated rats.

Gluconeogenesis was measured in parenchymal cells isolated from livers of rats 24 hours after carbon tetrachloride treatment. Glucose production from alanine and pyruvate was depressed, but glucose synthesis from lactate, glycerol, and fructose was unchanged by the haloalkane. Glucose-6-phosphatase activity was reduced 45%, but P-pyruvate carboxykinase and pyruvate carboxylase were not altered in activity. These results establish the gluconeogenic capabilities of cells which survive CCl₄ treatment and suggest that the cells isolated are representative of damaged cells rather than a normal population.     

Mechanism of a decrease of inducibility of tyrosine aminotransferase by carcinogenic aminoazo dyes. Absence of direct influence of o-aminoazotoluene on the enzyme molecules

The effect of o-aminoazotoluene (OAT) on the activity of tyrosine aminotransferase (TAT) from mouse liver cytosol under its incubation in the presence of the systems providing for the metabolic activation of the cancerogen (liver microsomes and NADPH2) and dephosphorylation of TAT molecules (light mitochondria and ATP) was studied. It was shown that OAT has neither direct nor indirect (via the phsophorylation--dephosphorylation systems) effect on the activity of TAT. It was concluded that the decrease of TAT induction by hydrocortisone in vivo resulting from injection of OAT to the mice is not due to the direct influence of the cancerogen on the enzyme molecules.     

Isolation of carcinogenic aminoazo dye-binding protein and its identification as alcohol dehydrogenase

A major carcinogenic aminoazo dye-binding protein having Ip of 9.7 (isoelectric focusing) was isolated from the liver cytosol of rats given 40 mg 3'MeDAB. The protein has the molecular weight of 6.8 × 10⁴ (gel-filtration) and two subunits of about 3.9 × 10⁴ molecular weight (SDS-polyacrylamide gel electrophoresis). The amino acid composition was similar to that reported for liver alcohol dehydrogenase of animals. The enzymatic activity was shown to be associated consistently with the dye-binding protein fractions throughout the purification steps suggesting identity of the dye-binding protein as liver alcohol dehydrogenase.     

Insulin responsiveness of isolated perfused livers from rats with streptozotocin induced diabetes.

The ability of insulin to inhibit efflux of potassium (K) and amino acid nitrogen (AAN) from perfused livers of normal and insulin deficient rats was studied. Two groups of rats with different degrees of insulin deficiency were produced by injecting varying amounts of streptozotocin. One group, classified as being moderately diabetic (MD), had fasting plasma glucose levels between 235--425 mg%, while the other group, whose plasma glucose levels greater than 425 mg%, were considered to have severe diabetes (SD). Two other groups of rats were food restricted in order to attain body weights comparable to the two groups of diabetic rats, and livers from these animals were used for control perfusions. The results indicated that the ability of insulin to suppress efflux of K and AAN from perfused livers of rats with MD was comparable to that seen in control perfusions. On the other hand, insulin could not suppress the efflux of either K or AAN from perfused livers of rats with SD. These results indicate that normal hepatic responsiveness to insulin can be lost secondary to the production of insulin deficiency.     

Metabolism of parenterally administered zinc and cadmium in livers of newborn rats

The interaction of injected zinc and cadmium with metallothionein was investigated in newborn rats. Tissues of 5-day-old rats were removed 24 h after a single injection (Sc) of saline or zinc (20 mg/kg, body wt.) or cadmium (1 mg/kg, body wt.) with 2.5 μCi of ⁶⁵Zn or ¹⁰⁹Cd or 5 μCi of [³⁵S]cysteine. Injection of zinc resulted in a 75% increase in the hepatic zinc concentration with a concomitant elevation of metallothionein (P < 0.001), zinc in metallothionein increased by 45% (P < 0.05); [³⁵S]cysteine incorporation indicated the induced synthesis of metallothionein. Injection of cadmium did not alter either metallothionein or zinc levels in liver, but cadmium in cytosol was preferentially bound to metallothionein. Neither treatment altered hepatic copper metabolism and copper in metallothionein, nor renal zinc and metallothionein levels. These data indicate that zinc injection can elevate hepatic zinc levels and induce metallothionein synthesis in newborn rats despite high basal levels; cadmium injection does not induce metallothionein synthesis, though cadmium is avidly sequestered by pre-existing metallothionein. The differences in the induction of metallothionein by these divalent cations can be explained by the differences in their binding affinities for thiol groups in intracellular metallothionein.     

Chemical structure of the O-polysaccharide isolated from Pectobacterium atrosepticum SCRI 1039

The lipopolysaccharide (LPS) of the bacterium Pectobacterium atrosepticum SCRI 1039 was hydrolyzed and the products were separated. A study of the obtained O-polysaccharide by means of chemical methods, GLC, GLC–MS, and NMR spectroscopy allowed us to identify a branched polymer with a pentasaccharide repeating unit of the structure shown below, in which the fucose residue was partially O-acetylated at C-2, C-3 or C-4.     

Carbohydrate composition of lipoprotein apoproteins isolated from rat plasma and from the livers of rats fed orotic acid

Dietary orotic acid has been shown to inhibit secretion of plasma lipoproteins from the liver and to cause the accumulation of lipoprotein apoproteins within the liver. Comparison of the carbohydrate composition of plasma apoproteins and corresponding apoproteins isolated from orotic acid induced fatty livers indicates that the latter are deficient in N-acetyl glucosamine, galactose, and N-acetyl neuraminic acid. These differences can be explained by a lack of exposure of liver apoproteins to glycosylating enzymes present in the Golgi apparatus.     

Formation of free acetate by isolated perfused livers from normal, starved and diabetic rats

Isolated rat livers perfused in an open system exhibited a continous net release of free acetate. Upon intraportal infusion of hexanoate the net release of total ketone bodies and of free acetate increased significantly in livers from fed and 48 hours starved rats. The ratio ketone body production/acetate production during infusion of hexanoate was similar with livers from fed and starved rats. Livers from diabetic rats, however, did not only exhibit a higher rate of ketone body and acetate production, but also a significant decrease of the ratio ketone body production/acetate production. Intraportal infusion of oleate led also to an enhanced release of free acetate. An examination of the activities of 5 enzymes involved in ketone body and acetate metabolism showed no correlation with the higher rate of acetate production by diabetic livers.     

Comparison of the properties of L-threonine dehydratase isolated from the livers of intact, adrenalectomized or cortisol-treated rats]

L-Threonine dehydratase preparations were isolated from liver of intact, treated with hydrocortisone and adrenalectomized rats. These preparations had different properties in stability, sensitivity to proteases and kinetic patterns. The preparations possessed also serine dehydratase activity, and the ratio threonine: serine activities was modified during the procedure of enzyme purification. It appears that the hormones affect not only the amount of enzyme proteins, but the qualitative properties of these proteins.