Depside as potent inhibitor of prostaglandin biosynthesis: a new active site model for fatty acid cyclooxygenase

Forty depsides and depsidones, the esters of phenolcarboxylic acids, were examined for their inhibitory effect against prostaglandin biosynthesis with rabbit renal microsomes. 4-0-Methylcryptochlorophaeic acid was the most active inhibitor so far tested and its IC50 value was 0.34 muM. Kinetic investigation has shown that this depside acts competitively with respect to arachidonic acid as most of the non - steroidal antiinflammatory drugs. X-Ray analysis has revealed that 4-0-methylcryptochlorophaeic acid maintains its rigid conformation by forming a strong hydrogen bond between the hydroxyl and methoxyl groups. Comparison of CPK models between 4-0-methylcryptochlorophaeic acid and non-steroidal antiinflammatory drugs revealed that the carboxyl group and the two rings of these drugs are almost superimposable to those of the depside. This finding led us to propose a new active site model based on the three dimentional structure of the depside.     

Contributions of subterranean termites to the “economy” of Chihuahuan desert ecosystems

Summary We examined the role of subterranean termites in decomposition of cattle dung, various herbaceous plant species and wood in a Chihuahuan desert ecosystem. From July–September, termites removed dung at a rate of 0.63 g day^-1 accounting for a percent mass loss of 19.5–100%. During the autumn subterranean termites consumed more than 50% of the leaves of the shrub Larrea tridentata, the grass Erioneuron pulchellum and annual plant Lepidium lasiocarpum and Baileya multiradiata but used very little of two other annuals Eriastrum diffusum and Eriogonum trichopes. Yucca inflorescence stalks on plots with termites lost 23% of their original mass in 30 months while those on termite free soils lost 11%. Elimination of termites resulted in reduction of fluff grass, Erioneuron pulchellum biomass, thereby affecting the structure of the ecosystem.     

Testicular androgens and spermatogenetic cycles in the viviparous lizard

Androstenedione, testosterone and dihydrotestosterone levels were measured in the testis of 36 males of the viviparous lizard throughout a period (from end of May to end of July) characterized by the transition between two spermatogenetic cycles and by very low levels of plasma testosterone. The sudden rise of testicular testosterone and androstenedione in June is concomitant with a degeneration of the seminiferous epithelium. It coincides with a transient appearance of testicular dihydrotestosterone. During the next decline in the levels of testosterone and androstenedione, it occurs a restoration of the seminiferous tubules which resume spermatogenesis (proliferation of spermatogenia and prophase of first meiotic division). The part played by some testicular steroids in the control of spermatogenesis is discussed.     

Antigen-binding receptors on T cells from long-term MLR. evidence of binding sites for allogeneic and self-MHC products

Antibody inhibition of radiolabelled stimulator membrane vesicle binding by T blasts activated in the mixed lymphocyte reaction (MLR) was used to identify responder-cell determinants involved in the binding phenomenon. Antisera or monoclonal antibodies against Thy-1, Lyt-1, Lyt-2 and Ly-6 antigens were not inhibitory. However, antibodies against heavy-chain V region (VH) determinants strongly inhibited vesicle binding by both primary and long-term MLR blasts. Anti-Ia (both alloantisera and monoclonal reagents) caused inhibition of antigen binding by primary MLR blasts only. T blasts from long-term MLR lines were neither Ia-positive, nor susceptible to blocking of antigen binding with anti-Ia. However, these cells were capable of specifically absorbing soluble syngeneic Ia material, with the concomitant appearance of vesicle-binding inhibition with anti-Ia sera. Acquisition of syngeneic Ia by T blasts was effectivelly blocked with the anti-VH reagent. Passively bound self-Ia did not interfere with vesicle binding in the absence of anti-Ia. These results strongly suggest the existance of specific self-Ia acceptor sites closely linked to the receptors for stimulator alloantigens on T cells proliferating in MLR. A receptor model based on these findings is briefly discussed.     

Effect of L-cystine on macromolecular changes during spore and parasporal crystal formation inBacillus thuringiensis var.thuringiensis

High concentration of L-cystine (0.25%) when present in a glucose-mineral salt medium inhibited sporulation-specific events like protease production, calcium uptake and dipicolinic acid synthesis inBacillus thuringiensis var.thuringiensis. In addition, the enzymes of the Krebs cycle from aconitase onwards were completely inhibited by a high concentration of cystine. At a low concentration of cystine (0.05%), none of the above mentioned macromolecular changes were affected. Lipid synthesis monitored by [1,2¹⁴ C]-acetate incorporation into lipid as well as into whole cells was completely inhibited.     

Spore and crystal formation inBacillus thuringiensis var.thuringiensis during growth in cystine and cysteine

The effect of the addition of different concentratons of cystine and cysteine on sporulation and parasporal crystal formation inBacillus thuringiensis var.thuringiensis was studied. The effect was well pronounced when the cystine/cysteine additions were made after the stationary phase. Heat stable spores and crystals were formed when the culture was provided with a low concentration of cystine/cysteine (0.05 per cent w/v). At a moderate concentration of cystine or cysteine (0.15%), only heat labile spores were formed without the production of the crystal. When the cystine/cysteine concentration was high (0.25%), spore and crystal formation were completely inhibited. Partial reversal of inhibition of sporulation was brought about by sodium sulphate or Zinc sulphate and lead, copper, cadmium or cobalt acetate at 0.2 mM or at 0.2% of sodium or potassium pyruvate, citrate, cisaconitate, oxalosuccinate, ∞ -keto-glutarate, succinate, fumarate, malate, or oxalacetate. Glutamate (0.2%) overcame the inhibitory effect of cystine/cysteine completely. The structural changes observed using phase contrast microscopy were dependent upon the concentration of cystine/cysteine.     

Pituitary corticotropin-inhibiting peptide: Properties and use in study of corticotropin action

The biological properties of the naturally occurring pituitary peptide α_h^7–38-adrenocorticotropin (ACTH) have been investigated. α_h^7–38-ACTH is devoid of steroidogenic activity but inhibits competitively ACTH-induced steroidogenesis in vitro as well as in vivo. The long-term actions of ACTH on normal and tumor adrenal cells in culture are also antagonized by α_h^7–38-ACTH. The apparent K_i for the inhibition of cyclic AMP production by α_h^7–38-ACTH (301 ± 62 nm) was significantly higher than the apparent K_i for the inhibition of corticosterone synthesis (21.6 ± 6.8 nm). Analysis of the inhibition of ACTH-induced steroidogenesis and cyclic AMP production in normal rat adrenocortical cells indicates that two separate receptors may be involved in mediating these responses.     

Polyglutamylfolate synthesis in Neurospora crassa: changes in pool size following growth in glycine- and methionine-supplemented media

The effect of media supplements on total and polyglutamylfolate concentrations has been examined in Neurospora crassa wild type (FGSC 853), an ethionine-resistant mutant (FGSC 1212), and a methionine auxotroph (FGSC 1330) which lacks folylpolyglutamate synthetase. When the culture medium contained 1 mm glycine, folate concentrations in the wild type were increased by over 90% and more p-[³H]aminobenzoate was incorporated into folates. Growth in l-methionine-supplemented media (1–5 mm) decreased folate levels and labeling in all three strains. In the wild type, this effect of l-methionine was reversed on transfer to unsupplemented media but p-[³H]aminobenzoate pulse-chase experiments suggested that exogenous methionine did not increase the turnover of labeled folates. At 1 mm, d-methionine did not affect polyglutamylfolate labeling but l-methionine reduced ³H incorporation by 65% in the wild type. Ion-exchange chromatography showed that p-[³H]aminobenzoate was incorporated in formyl- and methyltetrahydrofolates which in the wild type, were principally hexaglutamyl derivatives. Glycine-supplemented growth yielded labeled folates that were 24% heptaglutamates but these and pentaglutamates were lacking when l-methionine was supplied. The specific activity of GTP cyclohydrolase was not significantly affected by culture in l-methionine-containing media. Dialysis and gel filtration both lowered enzyme activities and product formation was not changed when up to 10 μmol of l-methionine was added to the reaction system. The data suggest that methionine or its metabolic products exerts some control over folate production which is distinct from the established inhibition of methylenetetrahydrofolate reductase by AdoMet.