On herbicidal actions

A theoretical interpretation of the herbicidal action of the 2,4-Dichlorophenoxyacetic acid is suggested.     

Anatomical and chemical defenses of conifer bark against bark beetles and other pests

Conifers are long-lived organisms, and part of their success is due to their potent defense mechanisms. This review focuses on bark defenses, a front line against organisms trying to reach the nutrient-rich phloem. A major breach of the bark can lead to tree death, as evidenced by the millions of trees killed every year by specialized bark-invading insects. Different defense strategies have arisen in conifer lineages, but the general strategy is one of overlapping constitutive mechanical and chemical defenses overlaid with the capacity to up-regulate additional defenses. The defense strategy incorporates a graded response from 'repel', through 'defend' and 'kill', to 'compartmentalize', depending upon the advance of the invading organism. Using a combination of toxic and polymer chemistry, anatomical structures and their placement, and inducible defenses, conifers have evolved bark defense mechanisms that work against a variety of pests. However, these can be overcome by strategies including aggregation pheromones of bark beetles and introduction of virulent phytopathogens. The defense structures and chemicals in conifer bark are reviewed and questions about their coevolution with bark beetles are discussed.     

Identification of heteroarylenamines as a new class of antituberculosis lead molecules

Enamine-containing analogues of heteroarylquinones were prepared based on initial screening data observed against Mycobacterium tuberculosis H37Rv (Mtb). Several analogues showed moderate to good inhibitory activity, with one analogue (7) also demonstrating acceptable toxic selectivity (MIC 0.39 microg/mL, SI 15). Activity towards a range of single-drug-resistant strains of Mtb was suggestive of a novel mechanism of action for 7.     

Physical changes of β-sitosterol crystals in oily suspensions during heating

The aim of this research was to describe the thermal behavior of β-sitosterol crystals in oil-suspensions with a focus on the role of water during heating. The suspensions were prepared by recrystallization in order to achieve a microcrystalline particle size. The structural changes together with the mechanical properties of the suspensions during heating were studied by using variable temperature X-ray powder diffractometry (VT-XRPD), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Hydrated β-sitosterol crystals in an oil-suspension, dehydrated, despite the composition of the suspensions, at low temperatures. At high β-sitosterol concentration, the monohydrate crystal form changed partially to a hemihydrated form, and when only a small amount of water was initially incorporated, the hemihydrate crystal form dehydrated to a mostly anhydrate crystal form. The released water, which was immiscible in the surrounding oil, caused the recrystallization of hydrated β-sitosterol during cooling. This procedure indicated a reversible dehydration process. Structural and thermal analysis of β-sitosterol crystals in suspensions, together with mechanical analysis made it possible to understand various physical changes during heating. Published: October 19, 2005     

Fluorometric polyethyleneglycol-peptide hybrid substrates for quantitative assay of protein disulfide isomerase

In eukaryotic cells the enzyme protein disulfide isomerase (PDI) is responsible for the formation and reshuffling of disulfide bonds in secretory proteins. The reaction carried out by PDI involves interaction with a highly complex mixture of polypeptide molecules that are in the process of folding. This means that PDI activity is typically measured in the context of a globular protein folding pathway. The absence of small, well-defined substrates for the quantitation of both oxidation and reduction reactions constitutes an inherent problem in the analysis of PDI activity. We describe a new type of substrate for PDI where two cysteine-containing oligopeptides are connected by an onameric ethylene glycol linker. We term such hybrid compounds PEGtides. The oligopeptides are each marked with a fluorescent aminobenzoic acid and a quenching nitrotyrosine group, respectively. The reversible formation of an intramolecular disulfide bond between fluorophore-containing and quencher-containing peptide segments results in a redox-dependent fluorescence signal. We find a model compound of this type to be a highly sensitive substrate for PDI both in oxidation and in reduction assays under steady state conditions. These aspects should make substrates of this type generally applicable for assaying PDI and other thiol-disulfide exchange enzymes.     

Energy expenditure, insulin, and VLDL-triglyceride production in humans

Hypertriglyceridemia is considered a cardiovascular risk factor in diabetic and nondiabetic subjects. In this study, we aimed to determine potential regulators of very low density lipoprotein-triglyceride (TG) production. VLDL-TG kinetics were measured in 13 men and 12 women [body mass index [mean (range)]: 24.8 (20.2-35.6) kg/m(2)]. VLDL-TG production was assessed from the plasma decay of a bolus injection of ex vivo labeled VLDL particles ([1-(14)C]triolein-VLDL-TG). Similar VLDL-TG production (micromol/min) was found in men and women. VLDL-TG production was not significantly correlated with palmitate flux ([9,10-(3)H]palmitate) (r = 0.09, P = 0.67) or palmitate concentration (r = -0.29, P = 0.2) but was correlated significantly with fasting insulin concentration (r = 0.46, P < 0.05) and resting energy expenditure (REE) (r = 0.45, P < 0.05). The latter correlation improved when adjusted for sex. The best multivariate model with VLDL-TG production as the dependent variable and REE, body composition, hormones, and substrate levels as independent variables included fasting insulin (P = 0.02) and REE (P = 0.02) (r(2) = 0.32, P < 0.001). We conclude that VLDL kinetics are similar in men and women and that REE and plasma insulin are significant independent predictors of VLDL-TG production. FFA availability and body fat distribution are unrelated to VLDL production. We suggest that REE plays a greater role in VLDL-TG production than previously anticipated. REE and insulin should be taken into account when VLDL-TG production comparisons between groups are made.     

Transposons inactivate biosynthesis of the nonribosomal peptide microcystin in naturally occurring Planktothrix spp

The filamentous cyanobacteria Planktothrix spp. occur in the temperate region of the Northern hemisphere. The red-pigmented Planktothrix rubescens bacteria occur in deep, physically stratified, and less eutrophic lakes. Planktothrix is a known producer of the toxic heptapeptide microcystin (MC), which is produced nonribosomally by a large enzyme complex consisting of peptide synthetases and polyketide synthases encoded by a total of nine genes (mcy genes). Planktothrix spp. differ in their cellular MC contents as well as the production of MC variants; however, the mechanisms favoring this diversity are not understood. Recently, the occurrence of Planktothrix strains containing all mcy genes but lacking MC has been reported. In this study, 29 such strains were analyzed to find out if mutations of the mcy genes lead to the inability to synthesize MC. Two deletions, spanning 400 bp (in mcyB; one strain) and 1,869 bp (in mcyHA; three strains), and three insertions (IS), spanning 1,429 bp (in mcyD; eight strains), 1,433 bp (in mcyEG; one strain), and 1,433 bp (in mcyA; one strain), were identified. Though found in different genes and different isolates and transcribed in opposite directions, IS were found to be identical and contained conserved domains assigned to transposable elements. Using mutation-specific primers, two insertions (in mcyD and mcyA) and one deletion (in mcyHA) were found regularly in populations of P. rubescens in different lakes. The results demonstrate for the first time that different mutations resulting in inactivation of MC synthesis do occur frequently and make up a stable proportion of the mcy gene pool in Planktothrix populations over several years.     

Modulation of fibrillation of hIAPP core fragments by chemical modification of the peptide backbone

The well-ordered cross β-strand structure found in amyloid aggregates is stabilized by many different side chain interactions, including hydrophobic interactions, electrostatic charge and the intrinsic propensity to form β-sheet structures. In addition to the side chains, backbone interactions are important because of the regular hydrogen-bonding pattern. β-Sheet breaking peptide analogs, such as those formed by N-methylation, interfere with the repetitive hydrogen bonding pattern of peptide strands. Here we test backbone contributions to fibril stability using analogs of the 6-10 residue fibril core of human islet amyloid polypeptide, a 37 amino acid peptide involved in the pathogenesis of type II diabetes. The Phe-Gly peptide bond has been replaced by a hydroxyethylene or a ketomethylene group and the nitrogen-atom has been methylated. In addition, we have prepared peptoids where the side chain is transferred to the nitrogen atom. The backbone turns out to be extremely sensitive to substitution, since only the minimally perturbed ketomethylene analog (where only one of the -NH- groups has been replaced by -CH(2)-) can elongate wildtype fibrils but cannot fibrillate on its own. The resulting fibrils displayed differences in both secondary structure and overall morphology. No analog could inhibit the fibrillation of the parent peptide, suggesting an inability to bind to existing fibril surfaces. In contrast, side chain mutations that left the backbone intact but increased backbone flexibility or removed stabilizing side-chain interactions had very small effect on fibrillation kinetics. We conclude that fibrillation is very sensitive to even small modifications of the peptide backbone.