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The nucleotide Zpp5'A2'p has been isolated from rat liver. Z stands for an unknown compound, probably a nucleoside. The preliminary structure of Zpp5'A2'p has been elucidated by treatment with phosphodiesterase and/or alkaline phosphatase and analysis of the products of the reaction by high pressure liquid chromatography. The following ultraviolet absorption spectral characteristics were determined at pH 7.0: Zpp5'A2'p (lambda max = 265 nm; A250/A260 = 0.76; A280/A260 = 0.83); Zp (lambda max = 280 nm; A250/A260 = 0.88; A280/A260 = 1.46). The molar extinction coefficient found for Zp, at 280 nm, was (7.5 + 0.9) X 10(3) M-1 cm-1. The base of Zp could correspond to an indole derivative.
Four sulfonamide veterinary drug residues were quantitated by electron-capture detection (ECD) after separation by gas chromatography (GC). The identities of sulfathiazole (ST), sulfamethazine (SM), sulfachloropyridazine (SCP), and sulfadimethoxine (SDM) were confirmed in bovine or swine liver residues by tandem mass spectrometry (MS/MS). Bovine or swine liver tissues were extracted by using either the Tishler or the Manuel-Steller cleanup. The methylated residues containing ST, SM, SCP, and SDM were separated by GC prior to MS/MS daughter ion analysis. Control tissue, control tissue fortified at 0.1 ppm, and incurred tissue residues at approximately 0.1 ppm were analyzed for these 4 sulfonamides. A Finnigan Model TSQ-46 operating in the chemical ionization mode was used to perform the MS/MS daughter ion experiments. The identities of all 4 sulfonamides were confirmed in a single GC/MS/MS analysis.
Purified extracts of alpha-antitrypsin cross-reacting material (CRM) from liver of patients with MM, ZZ, and MZ phenotypes were studied by acid-starch electrophoresis and crossed immunoelectrophoresis. It is believed that CRM-M from liver is derived primarily from postmortem digested serum antitrypsin, whereas CRM-Z is a product of postmortem digested antitrypsin from hepatocytes. All extracts produced small bands of antitrypsin on the cathodal side of the gel: A single M band migrated faster than the single Z band, whereas CRM from an MZ heterozygote produced a combination of 2 mobile bands. The CRM-Z (from a ZZ phenotype) did not migrate toward the anode, in contrast to the presence of a broad plateau of antitrypsin protein with CRM-M (from an MM phenotype) or CRM-MZ. Thus, most of the CRM-Z protein could not be accounted for on routine acid-starch electrophoresis. However, an anodal peak could be seen on starch gels with CRM-Z at less acidic pH, suggesting that the anodal-migrating CRM-Z protein is denatured and loses antigenicity at lower pH.
The ability of S-9 fractions isolated from the livers of 4-, 12-, and 26-month-old male inbred F344 rats to activate and metabolize the hepatocarcinogen aflatoxin B1 [(AFB1) CAS: 1162-65-8] was studied. The following observations were made: The activation of AFB1 to compounds that are mutagenic in the Ames Salmonella-microsome test and to compounds that covalently bind DNA in vitro was similar for liver S-9 from 4- and 12-month-old rats. A 30-50% decrease in the activation of AFB1 occurred in rats between 12 and 26 months of age. The in vitro metabolism of AFB1 to chloroform-soluble and water-soluble metabolites was similar for 4- and 12-month-old rats and decreased significantly in rats after 12 months of age. The proportion of most of the chloroform-soluble metabolites of AFB1 formed by liver S-9 from 4-, 12-, and 26-month-old rats was similar. However, the proportion of aflatoxicol (CAS: 29611-03-8) produced by liver S-9 increased approximately twofold in rats between 12 and 26 months of age. The cytochrome P450 content and the NADPH cytochrome c reductase activity of liver microsomes decreased 40-45% in rats between 12 and 26 months of age. However, the activities of UDPglucuronyltransferases and most forms of glutathione S-transferase did not change significantly with increasing age in liver microsomes and cytosol, respectively.
M. Kuwajima, C. B. Newgard, D. W. Foster, and J. D. McGarry (1986, J. Biol. Chem. 261, 8849-8853) have concluded that the reason postprandial hepatic glycogenesis occurs primarily from gluconeogenic precursors rather than glucose is because glucokinase activity is insufficient to support the observed rates of glycogen synthesis. F. L. Alvares and R. C. Nordlie (1977, J. Biol. Chem. 252, 8404-8414) have concluded that the combined activities of glucokinase and hexokinase are less than the apparent rates of hepatic glucose uptake. We have identified several factors in the assays used in these studies which lead to substantial underestimations of glucokinase activity. Glucokinase was assayed either by allowing glucose 6-phosphate to accumulate over 10 min (discontinuous assay) or by coupling the formation of glucose 6-phosphate with its oxidation by Leuconostoc mesenteroides glucose 6-phosphate dehydrogenase and NAD (continuous assay). Accurate determinations of glucokinase at 37 degrees C with subsaturating glucose require both 100 mM KCl and 2.5 mM dithioerythritol in the assay medium; 2-mercaptoethanol will not substitute for dithioerythritol. When both KCl and dithioerythritol are absent (Kuwajima et al.) glucokinase activity is underestimated by 3- to 5-fold. The discontinuous assay as used previously (Alvares and Nordlie) underestimates glucokinase activity in crude extracts by 2- to 2.5-fold, due in part to the hydrolysis of glucose 6-phosphate and its transformation to other hexose monophosphates. Under optimized conditions at 37 degrees C both assays yield similar results in extracts from fed rats, i.e., 2-3 and 4-5 units/g liver at 10 and 100 mM glucose, respectively. Some implications of the finding that total hepatic glucose phosphorylating capacity at physiological concentrations significantly exceeds the observed rates of postprandial glycogen synthesis are discussed.
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1. The activity of an enzyme catalysing the loss of O6-methylguanine from methylated DNA was increasing during liver regeneration after partial hepatectomy. Activity was increased 3-fold by 24h and was maximal (6-fold increase) over the period 48-72h after operation. 2. This activity could also be induced by chronic treatment with dimethylnitrosamine, but the maximal response amounted to a 2-3-fold change (with the greater effect in male rats) after 4-6 weeks of exposure to daily doses of 2 mg of dimethylnitrosamine/kg. 3. Neither partial hepatectomy nor treatment with dimethylnitrosamine increased the activities of two other enzymes repairing alkylated DNA, DNA (7-methylguanine-)glycosylase and DNA (3-methyladenine-)glycosylase. 4. These results therefore indicate that there is a selective induction of the O6-methylguanine removal system during hepatocyte proliferation. Since this product is known to lead to mutations and its persistence in DNA throughout cell replication has been implicated in tumour initiation, this induction may play a role in resistance to carcinogenesis by alkylating agents.
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