Chronic exposure to ionizing radiation as a tumor promoter in mouse skin.

We have tested chronic exposure to 90Y beta radiation for its action as a complete tumor promoter, a stage I tumor promoter, or a stage II tumor promoter in SENCAR mouse skin. In skin initiated with a single application of 7,12,dimethylbenz[a]anthracene (DMBA, 10 nmol), chronic exposure to beta radiation as a complete promoter (0.5 Gy, twice/week, 13 weeks) produced no tumors and, when added to a complete chemical promoter (TPA), reduced tumor frequency about 30%. A similar result was observed when beta radiation was tested as a stage II promoter. DMBA-initiated mice that received chemical (12-O-tetradecanoylphorbol-13-acetate, TPA) stage I promotion followed by 13 weeks of beta-radiation exposure (0.5 Gy, twice/week) as stage II promotion produced essentially no tumors, and combining the same chronic beta-radiation exposure with chemical (mezerein) stage II promotion reduced tumor frequency about 20% when compared to a similar group that was not irradiated. Chronic beta-radiation exposure was tested two ways as a stage I tumor promoter in initiated skin that was subsequently treated with mezerein as a stage II promoter. Stage I promotion was shown to proceed with the passage of time, indicating this process occurs naturally in the absence of chemical or physical stimulation. Hyperthermia, previously shown to be a potent inhibitor of chemically stimulated stage I promotion, had no effect on the natural process, indicating at least some differences in mechanism between the two processes. The natural process was, in fact, inhibited by chemical tumor promoters, but not by radiation. In addition to the increase resulting from this natural process, tumor frequency was further increased slightly but significantly (12-15%, P less than or equal to 0.05) when chronic radiation exposure was given as a stage I promoter (0.5 Gy, twice/week, 13 weeks) subsequent to initiation, in spite of the expected 20% reduction resulting from this dose. Exposure of initiated animals to radiation (0.5 or 1.0 Gy, twice/week, 2 weeks) in addition to TPA as stage I promotion produced a similar increase in tumor frequency (P less than 0.02). At higher radiation doses, however, tumor frequency was reduced compared to unirradiated controls. In a third test as a stage I promoter, beta radiation (0.5 Gy twice/week, 4 weeks) was given prior to initiation with N-methyl-N'-nitro-N-nitrosoguanidine in animals subsequently promoted by TPA (twice/week, 13 weeks), and again the radiation slightly but significantly (P less than 0.03) increased tumor frequency compared to the unirradiated control group.(ABSTRACT TRUNCATED AT 400 WORDS)     

Anionic Surfactant,Linear Alkyl Benzene Sulphonate Induced Oxidative Stress and Hepatic Impairments in Fish <Emphasis Type="Italic">Channa punctatus</Emphasis>

Linear alkyl benzene sulphonate (LAS), one of the main ingredients used in synthetic detergents to enhance their cleansing properties. Indiscriminate and untreated discharge of detergents and their residues in both lantic and lotic habitats pose a variety of ecological threats and also adversely affect aquatic fauna. In vivo, LAS metabolism and biotransformation occurs via monooxygenases in liver, leading to Reactive Oxygen Species, ROS, production and consequently oxidative stress by disturbing cellular antioxidant enzymatic equilibrium. Present study aims to evaluate the activities of two widely distributed antioxidant enzymes viz., catalase (CAT) and superoxide dismutase (SOD) and ROS induced histological impairments in liver of freshwater fish, Channa punctatus. For the estimation of oxidative stress and hepatic impairments, well acclimatized fishes were divided in three groups. Fish of group G1 serves as control whereas fish of the other two groups, G2 and G3 were exposed to two fractions, 1/20th and 1/10th of 96 h LC₅₀ of LAS for 24, 48, 72 and 96 h of exposure periods. Our results showed a significant induction in CAT and SOD activities in liver tissue of C. punctatus in a dose and time dependent manner. ROS induced histopathological impairments in hepatic tissues are characterized by loosely arranged, irregularly distributed and degenerated hepatocytes with increased vacuolization and pyknotic nuclei. The results are quite suggestive that LAS intoxication generates oxidative stress by ROS production which brings about histopathological impairments in exposed fish.     

Photoinhibition of photosynthesis without net loss of photosystem II components inPopulus deltoides

The photoinhibition of photosynthesis was investigated on intact attached leaves and isolated thylakoid membranes of Populus deltoides.Our studies demonstrate that in intact leaves photoinhibition takes place under high irradiance which is more pronounced at higher temperatures. No net loss of Dl and other proteins associated with photosystem II (PSII) were observed even after 64 % photoinhibition suggesting that the degradation of polypeptides associated with PSII is not the only key step responsible for photoinhibition as observed by other workers. Electron transport studies in isolated thylakoid membranes suggested water oxidation complex as one of the damaged site during high light exposure. The possible mechanisms of photoinhibition without net loss of D1 protein are discussed.     

Role of DNA barcoding in marine biodiversity assessment and conservation: An update

More than two third area of our planet is covered by oceans and assessment of marine biodiversity is a challenging task. With the increasing global population, there is a tendency to exploit marine resources for food, energy and other requirements. This puts pressure on the fragile marine environment and necessitates sustainable conservation efforts. Marine species identification using traditional taxonomical methods is often burdened with taxonomic controversies. Here we discuss the comparatively new concept of DNA barcoding and its significance in marine perspective. This molecular technique can be useful in the assessment of cryptic species which is widespread in marine environment and linking the different life cycle stages to the adult which is difficult to accomplish in the marine ecosystem. Other advantages of DNA barcoding include authentication and safety assessment of seafood, wildlife forensics, conservation genetics and detection of invasive alien species (IAS). Global DNA barcoding efforts in the marine habitat include MarBOL, CeDAMar, CMarZ, SHARK-BOL, etc. An overview on DNA barcoding of different marine groups ranging from the microbes to mammals is revealed. In conjugation with newer and faster techniques like high-throughput sequencing, DNA barcoding can serve as an effective modern tool in marine biodiversity assessment and conservation.     

Inhibition of glucose 6-phosphatase by pure and impure C-type phospholipases. Reactivation by phospholipid dispersions and protection by serum albumin.

1. Pure or impure C-type phospholipases hydrolysed rat liver microsomal phosphatides in situ at 5 degrees or 37 degrees C. At 5 degrees C mean hydrolysis of total phospholipids was 90% by Bacillus cereus and 75% by Clostridium perfringens (Clostridium welchii) C-type phospholipases. 2. Four degrees of inhibition of glucose 6-phosphatase (D-glucose 6-phosphate phosphohydrolase; EC 3.1.3.9) resulted. (a) At 37 degrees C inhibition was virtually complete and apparently irreversible. (b) At 5 degrees C phospholipase C inhibited 50-87% of the activity expressed by intact control microsomal fractions. (c) Bovine serum albumin present during delipidation alleviated most of this inhibition: at 5 degrees C phospholipase C plus bovine serum albumin inhibited by 0-35% (mean 18%):simultaneous stimulation by the destruction of its latency seems to offset glucose 6-phosphatase inhibition, sometimes completely. (d) If latency was first destroyed, phospholipase C plus bovine serum albumin inhibited 30-50% of total glucose 6-phosphatase activity at 5 degrees C. Only this inhibition is likely largely to reflect the lower availability of phospholipids, essential for maximal enzyme activity, as it is virtually completely reversed by added phospholipid dispersions. Co-dispersions of phosphatidylserine plus phosphatidylcholine (1:1, w/w) were especially effective but Triton X-100 was unable effectively to restore activity. 3. Considerable glucose 6-phosphatase activity survived 240min of treatment with phospholipase C at 5 degrees C, but in the absence of substrate or at physiological glucose 6-phosphate concentrations the delipidated enzyme was completely inactivated within 10min at 37 degrees C. However, 80mM-glucose 6-phosphate stabilized it and phospholipid dispersions substantially restored thermal stability. 4. It is concluded that glucose 6-phosphatase is at least partly phospholipid-dependent, and complete dependence is not excluded. For reasons discussed it is impossible yet to be certain which phospholipid class(es) the enzyme requires for activity.     

Design and synthesis of glucagon partial agonists and antagonists

The hyperglycemia and ketosis of diabetes mellitus are generally associated with elevated levels of glucagon in the blood. This suggests that glucagon is a contributing factor in the metabolic abnormalities of diabetes mellitus. A glucagon-receptor antagonist might provide important evidence for glucagons's role in this disease. In this work we describe how we combined structural modifications that led to glucagon analogues with partial agonist activity to give glucagon analogues that can act as competitive antagonists of glucagon-stimulated adenylate cyclase activity. Using solid-phase synthesis methodology and preparative reverse-phase high-performance liquid chromatography, we synthesized the following seven glucagon analogues and obtained them in high purity: [D-Phe4,Tyr5,Arg12]glucagon (2); [D-Phe4,Tyr5,Lys17,18]glucagon (3); [Phe1,Glu3,Lys17,18]glucagon (4); [Glu3,Val5,Lys17,18]glucagon (5); [Asp3,D-Phe4,Ser5,Lys17,18]glucagon (6); I4-[Asp3,D-Phe4,Ser5,Lys17,18]glucagon (7); [Pro3]glucagon (8). Purity was assessed by enzymatic total hydrolysis, by chymotryptic peptide mapping, and by reverse-phase high-performance liquid chromatography. The new analogues were tested for specific binding, for their effect on the adenylate cyclase activity in rat liver membranes, and for their effect on the blood glucose levels in normal rats relative to glucagon. Analogues showing no adenylate cyclase activity were examined for their ability to act as antagonists by displacing glucagon-stimulated adenylate cyclase dose-response curves to the right (higher concentrations). The binding potencies of the new analogues relative to glucagon (= 100) were respectively 1.0 (2), 1.3 (3), 3.8 (4), 0.4 (5), 1.3 (6), 5.3 (7), and 3 (8). Glucagon analogues 3-5 and 8 were all weak partial agonists with EC50 values of 500 (3), 250 (4), 1600 (5), and 395 nM (8), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of phospholipid fatty acids on the kinetics of high and low affinity sites of cytochrome c oxidase

The nature of the interactions between cytochrome c oxidase and the phospholipids in mitochondrial membranes has been investigated by varying the nature of the fatty acyl components of Saccharomyces cerevisiae. A double fatty acid yeast mutant, FAI-4C, grown in combinations of unsaturated (oleic, linoleic, linolenic, and eicosenoic) and saturated (lauric and palmitic) fatty acids, was employed to modify mitochondrial membranes. The supplemented fatty acids constituted a unique combination of different acyl chain lengths with varying degrees of unsaturation which were subsequently incorporated into mitochondrial phospholipids. Phosphatidylethanolamine and cardiolipin, the predominant phospholipids of the inner mitochondrial membrane, were characterized by their high levels of supplemented unsaturated fatty acids. Increasing the chain length or the degree of unsaturation of mitochondrial membrane phospholipids had no effect on altering the nature of the phospholipid polar head group but did result in a profound change on the specific activity of cytochrome c oxidase. When studied under conditions of different ionic strengths and pHs the enzyme's activity, as documented by Eadie-Hofstee plots, showed biphasic kinetics. The kinetic parameters for the low affinity reaction were greatly influenced by the changes in the membrane fatty acids and only marginal effects were noted at the high affinity reaction site. The discontinuities in the steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene, monitored at increasing temperatures, suggested that changes in membrane fluidity were conditioned by alterations in mitochondrial membrane fatty acid constituents. These results indicate that the lipid changes affecting the low affinity binding site of cytochrome c oxidase may be the result of lipid-protein interactions which lead to enzyme conformational changes or may be due to gross changes in membrane fluidity. It may, therefore, follow that this enzyme site may be embedded in or be juxtaposed to the outer surface of the inner mitochondrial membrane bilayer in contrast to the high affinity site which has been shown to be significantly above the membrane plane.