Exploratory studies on glucose 6-phosphatase and other liver enzymes.
This review will summarize the enzymatic steps and the genes in aflatoxin/sterigmatocystin biosynthesis.
(1958) Enzymatic O-methylation of epinephrine and other catechols.
To predict contact hypersensitivity, guinea pig models are available and have been used in risk assessment since the 1970s. Although sensitive and reproducible, these tests have limitations as they depend on subjective evaluation; this can be overcome by newer and more quantitative methods developed in the mouse. Regarding chemical-induced hypersensitivity induced by inhalation or ingestion of allergens, tests should be developed and evaluated in terms of their predictive value in man. When it comes to setting safe occupational exposure levels of potential allergens, consideration has to be given to the biphasic nature of allergy: the sensitization phase and the elicitation phase. The concentration required to elicit an allergic reaction in a previously sensitized individual is considerably lower than the concentration necessary to induce sensitization in the immunologically naïve but susceptible individual.
The common use of various medications can influence susceptibility to toxic chemicals mainly because many drugs bind to serum proteins and thus influence the transport, distribution or excretion rate of various toxic chemicals, or because many drugs are capable of inducing relevant detoxifying enzymes or depressing their activity (e.g., the cytochrome P450 enzymes), thus affecting the toxicity of chemicals with the same biotransformation pathway. Characteristic for either of the mechanisms is increased urinary excretion of trichloroacetic acid (the metabolite of several chlorinated hydrocarbons) when using salicylate, sulphonamide or phenylbutazone, and an increased hepato-nephrotoxicity of carbon tetrachloride when using phenobarbital. In addition, some medications contain a considerable amount of a potentially toxic chemical, for example, the aluminium-containing antacids or preparations used for therapeutic management of the hyperphosphataemia arising in chronic renal failure.
Enzyme Reactions and Genes in Aflatoxin Biosynthesis
The thymic status is also dependent on nutritional status (Van Logten et al., 1981; Corman, 1985; Mittal et al., 1988; Good & Lorenz, 1992), and stressful conditions influence the appearance of lymphoid organs, especially the thymus.
Another relatively simple assay for cytotoxicity is the MTT test. MTT (3[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) is a tetrazolium dye that is reduced by mitochondrial enzymes to a blue colour. Only cells with viable mitochondria will retain the ability to carry out this reaction; therefore the colour intensity is directly related to the degree of mitochondrial integrity. This is a useful test to detect general cytotoxic compounds as well as those agents that specifically target mitochondria.
Aflatoxin Biosynthesis and Genes of Aspergillus parasiticus
The terminal step in cocaine biosynthesis is catalyzed by an acyltransferase that utilizes benzoyl-CoA and methylecgonine as substrates and is localized to the spongy mesophyll .
The OAVN cyclase was purified from the cytosol of A. parasiticus NIAH-26 as previously described (). The enzyme was subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the protein (79 kDa) on the gel was applied to an automated sequencer. Twenty-five amino acid residues at the N terminus of OAVN cyclase were sequenced (Fig. ). BLAST analysis unexpectedly revealed that the resultant sequence was the same as that of a stretch (amino acids 42 to 66) of VHOH cyclase (VBS) that was deduced from the vbs gene of A. parasiticus SU-1 (accession no. and ) (, ). N-terminal amino acid residues 1 to 41 in the VHOH cyclase of SU-1 were not found in the OAVN cyclase of NIAH-26. We also confirmed that the purified OAVN cyclase catalyzed the production of VB from VHOH, when VHOH was used as the substrate instead of OAVN in a preliminary experiment (data not shown). During all steps through purification of the OAVN cyclase, we did not recognize OAVN cyclase activity other than the main activity (), suggesting that the purified enzyme is the sole or at least a major enzyme involved in the reaction from OAVN to AVR or from VHOH to VB. These results suggested that the same enzyme catalyzes the two different reactions, from OAVN to AVR and from VHOH to VB, in aflatoxin biosynthesis.
Enzyme reactions and genes in aflatoxin ..
Enzyme reactions and genes in aflatoxin biosynthesis
This review will summarize the enzymatic steps and the genes in aflatoxin/sterigmatocystin biosynthesis."
Enzyme reactions and genes in aflatoxin biosynthesis ..
This effect may alter cell membrane fluidity and may explain the sublethal effect of benzene on lymphocyte function.
Enzyme reactions and genes in aflatoxin biosynthesis.
The reactions require molecular oxygen and nicotinamide adenine dinucleotide phosphate, reduced form (NADPH).
reactions and genes in aflatoxin biosynthesis.
Functionally, cell-mediated immunity appears to be suppressed in a dose-dependent fashion, as manifested in delayed-type hypersensitivity responses, rejection of allogeneic skin transplants, graft-versus-host reactivity, and lymphocyte proliferation in vitro after mitogen stimulation.
Enzyme reactions and genes in aflatoxin biosynthesis
The battery of in vitro tests that is used as part of this tier-testing strategy depends upon the needs of the particular industry. Eye irritation testing is done by a wide variety of industries from cosmetics to pharmaceuticals to industrial chemicals. The type of information required by each industry varies and therefore it is not possible to define a single battery of in vitro tests. A test battery is generally designed to assess five parameters: cytotoxicity, changes in tissue physiology and biochemistry, quantitative structure-activity relationships, inflammation mediators, and recovery and repair. An example of a test for cytotoxicity, which is one possible cause for irritation, is the neutral red assay using cultured cells (see above). Changes in cellular physiology and biochemistry resulting from exposure to a chemical may be assayed in cultures of human corneal epithelial cells. Alternatively, investigators have also used intact or dissected bovine or chicken eyeballs obtained from slaughterhouses. Many of the endpoints measured in these whole organ cultures are the same as those measured in vivo, such as corneal opacity and corneal swelling.
Enzyme reactions and genes in aflatoxins biosynthesis.
Rats treated with total body irradiation and syngeneic or autologous bone-marrow transplantation, followed by treatment with cyclosporin A at a dose of about 10 mg/kg body weight per day subcutaneously for four weeks, developed signs of acute graft-versus-host reactions, with lymphocytic infiltration at multiple epithelial sites (Glazier et al., 1983).
associated genes and/or knocking down aflatoxin biosynthesis ..
Although this approach cannot, in itself, provide information that may be obtained in studies on intact animals, it can, coupled with knowledge of the physicochemical properties of the compound and the kinetics of enzymatic biotransformation reactions in tissues of various species, provide a logical basis for selection of species for long-term toxicity tests.
"I have always been impressed by the quick turnaround and your thoroughness. Easily the most professional essay writing service on the web."
"Your assistance and the first class service is much appreciated. My essay reads so well and without your help I'm sure I would have been marked down again on grammar and syntax."
"Thanks again for your excellent work with my assignments. No doubts you're true experts at what you do and very approachable."
"Very professional, cheap and friendly service. Thanks for writing two important essays for me, I wouldn't have written it myself because of the tight deadline."
"Thanks for your cautious eye, attention to detail and overall superb service. Thanks to you, now I am confident that I can submit my term paper on time."
"Thank you for the GREAT work you have done. Just wanted to tell that I'm very happy with my essay and will get back with more assignments soon."