The sesquiterpene lactone hymenoxon acts as a bifunctional alkylating agent

Hymenoxon, a toxic sesquiterpene lactone found in bitterweed, bound deoxyguanosine in a cell free system and formed adducts with guanine residues in cellular DNA. The reactive dialdehyde form of hymenoxon formed stable Schiff base products with deoxyguanosine which were separable from unreacted hymenoxon and deoxynucleosides by reverse phase high pressure liquid chromatography. Hymenoxon adducts which eluted as a single impure peak from the octadecylsilane column separated on amino and diphenyl-bonded phases with 10% methanol. Tritiated nucleoside adducts were isolated and purified from CFW mouse sarcoma cells treated with hymenoxon. Proton nuclear magnetic resonance spectra of purified hymenoxon-deoxyguanosine adducts revealed a loss of signals for hydroxyl groups in the bishemiacetal of hymenoxon. ¹³C-nuclear magnetic resonance spectra revealed that the major adduct has 35 carbon atoms, indicating an interaction of at least two guanine residues per hymenoxon molecule and suggesting that hymenoxon may cross-link DNA. Sedimentation analysis of treated DNA further showed that DNA cross-linking by hymenoxon (30 µg/ml) was equivalent to that of a known cross-linking agent, mitomycin C (7.5 µg/ml). Hymenoxon was more cytotoxic to DNA cross-link repair-deficient Chinese hamster ovary cell mutants than to repair proficient strains. These data combine to indicate that hymenoxon acts as a bifunctional alkylating agent which cross-links DNA in mammalian cells.CHO Chinese hamster ovary - HYM hymenoxon - MMC mitomycin C - NMR nuclear magnetic resonance - PBS phosphate buffered saline     

Properties of the reaction center of the thermophilic purple photosynthetic bacterium Chromatium tepidum

Reaction centers were purified from the thermophilic purple sulfur photosynthetic bacterium Chromatium tepidum. The reaction center consists of four polypeptides L, M, H and C, whose apparent molecular masses were determined to be 25, 30, 34 and 44 kDa, respectively, by polyacrylamide gel electrophoresis. The heaviest peptide corresponds to tightly bound cytochrome. The tightly bound cytochrome c contains two types of heme, high-potential c-556 and low-potential c-553. The low-potential heme is able to be photooxidized at 77 K. The reaction center exhibits laser-flash-induced absorption changes and circular dichroism spectra similar to those observed in other purple photosynthetic bacteria. Whole cells contain both ubiquinone and menaquinone. Reaction centers contain only a single active quinone; chemical analysis showed this to be menaquinone. Reaction center complexes without the tightly bound cytochrome were also prepared. The near-infrared pigment absorption bands are red-shifted in reaction centers with cytochrome compared to those without cytochrome.     

In support of the trap hypothesis. Chymotrypsin is not rigidly held in its complex with human alpha 2-macroglobulin

Complexes (2:1) of chymotrypsin with human alpha 2-macroglobulin have been prepared in the presence of 200 mM methylamine such that 90% of the chymotrypsin remains noncovalently bound to the alpha 2-macroglobulin. Reaction of this complex with the active-site-directed spin-labeling reagent 4-[(ethoxyfluorophosphinyl)oxy]-2,2,6,6-tetramethylpiperidinyl+ ++-1-oxy results in nitroxide labeling of the active-site serine residue of the complexed chymotrypsin. Electron spin resonance (ESR) spectra of this complex were recorded at 275 K in buffer and at 263 K in 50% glycerol. At 263 K in 50% glycerol the spectrum is that expected for a rigid glass, whereas at room temperature the ESR spectrum shows that the chymotrypsin is only slightly immobilized compared with free spin-labeled chymotrypsin. These findings are discussed in relation to possible models of inhibition of protease activity by alpha 2-macroglobulin. It is concluded that the trap mechanism of Barrett and Starkey [Barrett, A. J., & Starkey, P. M. (1973) Biochem. J. 133, 709-724] is the only model currently considered that can account for the present findings.     

alpha-D-mannopyranosylmethyl-p-nitrophenyltriazene inhibition of rat liver alpha-D-mannosidases

The compound alpha-D-mannopyranosylmethyl-p-nitrophenyltriazene (alpha-ManMNT) has been tested for its effect on four alpha-D-mannosidase activities present in rat liver. When p-nitrophenyl alpha-D-mannopyranoside was used as a substrate, preincubation of enzyme with 1.0 mM alpha-ManMNT inhibited soluble alpha-D-mannosidase by 90%, lysosomal alpha-D-mannosidase by approx. 60%, and had virtually no effect on Golgi mannosidase II. Golgi mannosidase I removal of the four alpha-1,2-linked D-mannoses from the common Man9GlcNAc2 oligosaccharide structure formed during N-linked glycoprotein biosynthesis was also blocked by treatment of the Golgi fraction with this compound. Mannosyltriazene inhibition of the three susceptible hepatic alpha-D-mannosidases was largely irreversible. alpha-ManMNT should therefore be useful for studying oligosaccharide processing and possibly for determining the turnover time of the inhibited alpha-D-mannosidases.     

Effects of propoxur exposure on females of the German cockroach, Blattela germanica and their oothecae

Susceptible and insecticide resistant females of Blattella germanica (L.), Dictyoptera, were exposed to propoxur treated surfaces. They carried oothecae that were expected to hatch in 48 to 72 h. Hatch was delayed in females that retained their oothecae throughout the exposure period. Oothecal hatch and nymphal survival were reduced when oothecae hatched on a treated surface but not when oothecae were retained and hatched on an insecticide-free surface. Over half of the susceptible strain females dropped their oothecae during the exposure period while very few resistance females dropped oothecae prematurely. Mortality of susceptible females that dropped their oothecae was higher than among those that retained oothacea. A tendency in this direction was apparent among the few resistant females that dropped their oothecae. The number of nymphs that emerged on the treated surface and also that survived for 24 h was higher in the resistant than in the susceptible strain. Newly hatched nymphs were frequently attached to the oothecae due to an inability to shed the embryonic cuticle.

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Résumé Des femelles de B. germanica, sensibles ou résistantes aux insecticides, ont été mises en présence de surfaces traitées au propoxure. Elles portaient des oothèques dont l'éclosion était attendue entre 48 et 72 h plus tard. Les éclosions ont été retardées, les femelles ayant conservé leurs oothèques pendant toute la période d'exposition. Lex taux d'éclosion des oothèques et de survie larvaire ont été normaux quand il y a eu rétention de l'oothèque et émission sur une surface saine, par contre ils étaient réduits quand l'oothèque a été émise sur une surface traitée. Plus de la moitié des femelles de la souche sensible ont laché leur oothèque pendant la période d'exposition tandis que très peu de femelles de la souche résistante ont abandonné leur oothèque prématurément. La mortalité était plus élevée chez les femelles sensibles qui ont perdu leur oothèque que chez celles qui l'avaient conservée. Une tendance du même type était décelable parmi les quelques femelles de la souche résistante qui perdirent leur oothèque. Le nombre d'écolosions de larves et le nombre de survies larvaires à 24 h étaient plus élevés dans la souche résistante que dans la souche sensible. Les larves néonates étaient souvent fixées à l'oothèque par suite de leur incapacité à se dépouiller de la cuticle embryonnaire.

     

Convergence to equilibrium in a genetic model with differential viability between the sexes

A single locus, diallelic selection model with female and male viability differences is studied. If the variables are ratios of allele frequencies in each sex, a 2-dimensional difference equation describes the model. Because of the strong monotonicity of the resulting map, every initial genotypic structure converges to an equilibrium structure assuming that no equilibrium has eigenvalues on the unit circle.Partially supported by funds provided by a Science and Education Grant to the USDA-Forest Service, Southeastern Forest Experiment Station, Population Genetics of Forest Trees Research Unit, Raleigh, USASupported by a grant from the Max Kade Foundation, New York, USA