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1.
While metabolism of benz[a]anthracene by rat liver microsomes produced a (+)5R,6R-dihydrodiol as the major enantiomer, metabolism of 12-methylbenz[a]anthracene under similar conditions gave a (?)5S,6S-dihydrodiol as the major enantiomer. This is the first example indicating that the methyl substituent of a polycyclic aromatic hydrocarbon can drastically alter the stereoselective preference of the microsomal drug-metabolizing enzyme systems toward a substrate molecule in the formation of a dihydrodiol metabolite at an unsubstituted aromatic double bond.  相似文献   

2.
We have measured the cytotoxicity of thymidine to C3H10T12 mouse embryo fibroblasts derived from morphologically transformed foci of cells from cultures exposed to chemical carcinogens. Four of these cell lines have previously been shown to be tumorigenic in irradiated syngeneic hosts and were all more sensitive to the lethal effects of thymidine than were the non-transformed cells. Strikingly, the most tumorigenic of the cell lines were most sensitive to thymidine. Differences in plating efficiencies or growth rates of the various cell lines were not associated with differences in thymidine sensitivity.  相似文献   

3.
Formycin B, a pyrazolo(4,3-d)pyrimidine C-nucleoside, inhibited the growth of Leishmaniadonovani promastigotes in culture with an ED90 of 0.2 μg/ml. Promastigotes incubated for 24 hrs with Formycin B at 10 μg/ml were found to convert it to the ribonucleotide, formycin B 5′-monophosphate. The parasites were also capable of aminating formycin B 5′-monophosphate as evidenced by the appearance of formycin A di- and triphosphate. The RNA contained the formycin A moiety in 3′,5′-polynucleotide linkage. Succino-AMP synthetase from these parasites was able to use formycin B 5′-monophosphate as an alternate-substrate with a K'm of 26 μM and a V'm of about 1% the V'm IMP. Formycin B 5′-monophosphate was also a substrate for mammalian succino-AMP synthetase with a Vm' of 40% the Vm' of IMP.  相似文献   

4.
Clostridium difficile produces two toxins, an enterotoxin and a cytotoxin. The enterotoxin was purified using fast methods (tangential flow filtration, fast protein liquid chromatography). The purified enterotoxin is composed of two subunits (A1 = 41,500, A2 = 16,000) and its pI is 3.5.  相似文献   

5.
The effect of Dermatophiluscongolensis on reproductive performance and milk production of dairy cattle was investigated using a prospective cohort study design. The following results were obtained: the calving to conception interval was 122 vs 104 days (P<0.05) for cows with lesions (cases) and those without lesions (non-cases), respectively; the 180-day pregnancy rate was 70.3% vs 84.3% (P<0.02) for cases and non-cases, respectively; the interval to first service was 69 days for cases and 64 days for non-cases (P<0.05) and the interval from first to second service was 32.7 days for cases and 49.4 days (P<0.01) for non-cases. The prevalence of cows with lesions was 33% (66200). Lesions were most commonly found on the skin covering the coccygeal and sacral vertebrae and the gluteal muscles. White skin had a greater prevalence of lesions than did black skin (P<0.05).  相似文献   

6.
Naphthylmercaptobenzoquinone (NMBQ) inhibits photophosphorylation in Rhodospirillumrubrum chromatophores. The endogenous unsupplemented system is the most sensitive one being 50% inhibited by 0.5 μM NMBQ, whereas 20 μM are required for 50% inhibition of photophosphorylation in the presence of N-methylphenazonium methosulfate or diaminodurene. The inhibition is less effective under argon, especially in the presence of ascorbate, and is reversed on addition of various naphthoquinones, which can also reverse the inhibition of photophosphorylation by dibromothymoquinone (DBMIB). Another quinone analog, dodecylmercaptonaphthoquinone (DMNQ), inhibits endogenous photophosphorylation even more effectively than NMBQ, but its inhibition is not reversed by the added naphthoquinones. It is concluded that NMBQ and DBMIB, but not DMNQ, inhibit photophosphorylation in chromatophoresby acting as antagonists of ubiquinone.  相似文献   

7.
It is demonstrated that two classes of binding site for acetylcholine are present on Torpedocalifornica acetylcholine receptor. One class is the well documented site on each of the two subunits of 40,000 daltons, which can be covalently modified by bromocetylcholine. Both in the absence and in the presence of bromoacetylcholine another binding site is shown to exist by virtue of acetylcholine dependent fluorescence changes in the receptor covalently modified by 4-[N-(iodoacetoxy)ethyl-N-methyl]-amino-7-Nitrobenz-2-oxa-1,3 diazole (IANBD). This site has a low affinity for acetylcholine (Kd ~ 80 μM) that corresponds closely with the known concentration dependence of acetylcholine mediated activation of this receptor and we conclude that it may represent a site of association that participates in channel opening in this system.  相似文献   

8.
Trypsin treatment of intact Escherichia coli Crookes cells is a probe for analyzing the functioning of protein sites in thiamine transport. These sites are cryptic since cells with different levels of thiamine transport activity respond differently to trypsin treatment. Mild trypsin treatment of cells with normal transport activity enhanced the velocity of uptake and decreased the capacity; more rigorous treatment reduced both parameters. Cells with low activity showed greatly increased rates of uptake and capacities under all but the mildest treatment conditions. These observations are consistent with a trypsin unmasking of thiamine transport sites in low activity cells and a destruction of the sites in higher activity cells.  相似文献   

9.
The linkage pattern of the K6-antigen was investigated using material from the urinary pathogen, Escherichia coli LP 1092. The polysaccharide consists of ribose and 3-deoxy-D-manno-2-octulosonate (KDO) in a ratio of 2:1. Colorimetric procedures, Smith degradation, methylation analysis, and nuclear magnetic resonance spectroscopy were applied to the whole polysaccharide and to a trisaccharide “repeating unit” obtained by mild-acid catalyzed hydrolysis. Together, the data are compatible only with a branched chain structure …3Ribfβ1→7KDOpβ2→3Ribfβ
  相似文献   

10.
A 105,000 x g residue fraction of Mycobacteriumsmegmatis contains an enzyme (acyl transferase) that transfers endogenous mycolic acid to trehalose monomycolate to yield trehalose dimycolate. This enzyme activity is stable to repeated freezing and thawing and is unaffected by the antimycobacterial drug, ethambutol. These results show that trehalose monomycolate is a direct precursor of trehalose dimycolate and suggest the presence of activated mycolic acids (acyl donor) in the cell-free system.  相似文献   

11.
Hydrocortisone increases rat liver tryptophan oxygenase mRNA activity as measured by a translational assay. Pretreatment of rats with cycloheximide thirty minutes before hydrocortisone administration largely prevents the hormonal induction of tryptophan oxygenase mRNA. Tryptophan oxygenase mRNA activity begins to increase after a lag of at least 30 to 60 minutes after hydrocortisone injection. These results suggest that the synthesis of intermediary protein(s) is required for the induction of tryptophan oxygenase mRNA by glucocorticoids.  相似文献   

12.
The liver fluke, Fasciola hepatica, has a very active adenylate cyclase which can be stimulated by NaF or by serotonin and guanine nucleotides. Micromolar amounts of AlCl3 augment the activation by F-. In contrast, when the enzyme is activated with serotonin and guanine nucleotides, AlCl3 inhibits the activation. Aluminum also inhibits the activation by forskolin. Gallium mimics the effects of aluminum.  相似文献   

13.
A rapid procedure to study the interaction of carcinogens with DNA in cultured cells has been developed. The cells, which are labeled with 7,12-[3H]dimethylbenz[a] anthracene ([3H]DMBA), are lysed with 0.24 M phosphate buffer (pH 6.8), 1% sodium dodecyl sulfate (SDS), 8 M urea and 0.01 M ethylenediamine-tetraacetate (EDTA) and sonicated. The cell lysates are fractionated on columns of hydroxylapatite. Proteins and RNA are removed with 8 M urea in 0.24 M phosphate buffer (pH 6.8). DMBA-bound DNA is eluted with 0.4 M phosphate buffer (pH 6.8). DMBA-DNA isolated by this procedure is virtually free from proteins and RNA. Thermal stability, ultraviolet spectra and the density of DNA is not altered by DMBA binding. The uptake of DMBA by mouse epidermal cells is rapid and the binding of DMBA to DNA is linear for the first 8 h of exposure. DMBA binds to DNA in all phases of the cell cycle. However, the highest binding occurs immediately following maximum DNA synthesis.  相似文献   

14.
A partially purified preparation of pyridine nucleotide transhydrogenase (E.C. 1.6.1.1.) (energy-independent) has been obtained from membranes of Escherichiacoli by means of deoxycholate extraction and DEAE-cellulose chromatography in the presence of Triton X-100. The enzyme was lipid-depleted by treating with cholate and ammonium sulfate. The preparation was reactivated by various phospholipids, in particular, bacterial cardiolipin and phosphatidyl glycerol. Phosphatidyl ethanolamine, the major phospholipid in the outer membrane of E.coli, was relatively ineffective in stimulating activity. The membrane-bound pyridine nucleotide transhydrogenase is slowly inhibited by N-ethylmaleimide. Protection against inhibition was achieved with NAD+ and NADP+, but NADPH served to accelerate the rate of inhibition.  相似文献   

15.
The effects of divalent ions on fully charged poly(S-carboxymethyl-l-cysteine) have been examined using circular dichroism for eight species: CuCl2, CdCl2, ZnCl2, NiCl2, CoCl2, BaCl2, CaCl2, and MgCl2. Five of them are effective inducers of β-form in the order: Cu2+Cd2+Zn2+Ni2+Co2+, in media with no salt added. However, the other three ions (Ba2+, Ca2+ and Mg2+), are not effective. Precipitation occurs when metal chlorides reach the vicinity of the equivalent point except for Ca2+ and Mg2+. Precipitation of the random coil form is slow, while that of the β-form is rapid. Addition of NcCl reduces the solubility of the β-form considerably. The pH value varies linearly with the logarithm of metal chloride concentration CM for Ba2+, Ca2+ and Mg2+ ions, while nonlinear dependence of pH on log CM is found for Cu2+, Ni2+ and Co2+ ions.  相似文献   

16.
Compound 4880, a condensation product of N-methyl-p-methoxyphenethylamine with formaldehyde, is composed of a family of cationic amphiphiles differing in the degree of polymerization. Compound 4880 was found to be a potent inhibitor of the calmodulin-activated fraction of brain phosphodiesterase and red blood cell Ca2+-transport ATPase, with IC50 values of 0.3 and 0.85 μg/ml, respectively. However, the basal activity of both enzymes is not at all suppressed by the drug at concentrations up to 300 μg/ml. Inhibition of Ca2+ transport into inside-out red blood cell vesicles by compound 4880 follows a similar pattern in that basal, calmodulin-independent, transport is also not affected by the drug. Kinetic analysis revealed that the stimulation of Ca2+-transport ATPase induced by calmodulin is inhibited by compound 4880 according to a competitive mechanism. It was demonstrated that the inhibitory constituents of compound 4880 bind to calmodulin in a Ca2+-dependent fashion. Comparison of the specificity of several anti-calmodulin drugs showed that compound 4880 is the most specific inhibitor of the calmodulin-dependent fraction of red blood cell Ca2+-transport ATPase that has been described hitherto. In addition, compound 4880 was found to be a rather specific inhibitor of the calmodulin-induced activation of Ca2+-transport ATPase when compared with the stimulation induced by an anionic amphiphile or by limited proteolysis. Half-maximal inhibition of the activity stimulated by oleic acid or mild tryptic digestion required 8- and 32-times higher concentrations of compound 4880, respectively, compared with the calmodulin-dependent fraction of the ATPase activity. Moreover, calmodulin-independent systems as rabbit skeletal muscle sarcoplasmic reticulum Ca2+-transport ATPase or calf cardiac sarcolemma (Na+ + K+)-transport ATPase are far less influenced by compound 4880 as compared with trifluoperazine and calmidazolium. Because of its high specificity compound 4880 is proposed to be a promising tool for studying calmodulin-dependent processes.  相似文献   

17.
Pretreatment of rats by ellipticines enhanced the microsomal concentration of cytochrome P-450, benzo[a]pyrene (BP) metabolism and activation and, to a smaller extent, ethoxycoumarin deethylation, but not acetanilide hydroxylation. This increased BP biotransformation was essentially due to the formation of bay-region metabolites, BP 9,10-diol, BP 7,8-diol and 9-hydroxy-BP, or to the formation of BP 7,8-diol-9,10-epoxide- and of 9-hydroxy-BP 4,5-oxide-DNA adducts. In the ellipticine series, 9-fluoroellipticine (9-FE) presents a slight inducing potency compared with the parent and 9-hydroxy molecules. Pretreatment of mice with 9-hydroxyellipticine (9-OHE) led also to an increased mutagenicity of BP and to an augmentation of skin carcinogenesis by 7,12-dimethylbenz[a]anthracene (DMBA). These results clearly show that 9-OHE induces the biosynthesis of cytochrome P-450 which markedly stimulates the mutagenic and carcinogenic potentialities of polycyclic aromatic hydrocarbons (PAH).  相似文献   

18.
The composition of the C-terminal end of a variant surface glycoprotein from Trypanosoma equiperdum (BoTat-1 VSG) has been examined. It has been reported for two Trypanosoma brucei VSGs (Holder, A.A., Biochem. J. (1983), 209, 261–262) that ethanolamine was involved in binding the C-terminal amino acid to an oligosaccharide side chain. Tryptic glycopeptides were prepared from BoTat-1 VSG and analyzed. One of them was found to contain ethanolamine and consequently was assumed to be C-terminal. It was shown that the glycopeptide also included phosphate, glycerol and fatty acids. The fatty acid composition was representative of that of glycerolipids. All the results suggest that the end of the molecule is a core of phosphatidylethanolamine.  相似文献   

19.
The utility of an iodinated derivative of inulin (125I-tyraminyl-inulin, 125ITI) for reporting in vivo tissue distributions of liposomal contents is described. It is shown, employing a rat model, that this probe satisfies the criteria that the free form is rapidly cleared from the circulation and excreted, whereas 125ITI encapsulated in large unilamellar vesicle (LUV) systems and subsequently taken up in various tissues exhibits a long (>3 days) retention time. Further, high specific activities (>1 μCi per μ1) are easily achievable, allowing low LUV dose levels (≤2.5 μmole phospholipid/kg body weight) to be employed. Minimal tissue workups for quantitation of 125ITI distributions are required. It is concluded that from criteria of sensitivity, expense and simplicity, 125ITI is a most convenient probe for characterizing liposome deposition in vivo.  相似文献   

20.
The Na+-independent leucine transport system is resolved into two components by their different affinity (Km about 44 μM and 8.0 mM) for leucine in the Chang liver cell. Treatment of the cells with N-ethylmaleimide (1 mM) specifically stimulates the high-affinity component of the Na+-independent system by greatly increasing its Vmax value, whereas the Vmax value of the low-affinity component is markedly lowered. The stimulatory effect of N-ethylmaleimide on leucine transport is reduced by prior treatment of the cells with 2,4-dinitrophenol, but this phenomenon seems to be irrelevant to the ATP-depleting action of the uncoupler. The treatment with 2,4-dinitrophenol has been found not to be inhibitory on the subsequent Na+-independent leucine uptake itself. Treatment with dibucaine, a phospholipid-interacting drug, also reduces to varying degrees (depending on its concentration) the stimulatory effect of N-ethylmaleimide on the subsequent leucine uptake, although pretreatment with dibucaine can stimulate the Na+-independent leucine uptake itself. We conclude that the stimulatory effect of N-ethylmaleimide on leucine transport is not correlated with the energy level of cell, but involves the perturbation of the membrane bilayer structures.  相似文献   

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