Endor and ESR studies of spin-trapped radicals in autoxidized unsaturated fatty acid methyl esters

Radicals generated in autoxidized methyl oleate, linoleate and linolenate have been detected by ESR and ENDOR using the spin trap 2-methyl-2-nitrosopropane, this being the first report of ENDOR spectra on such systems.     

Molecular Mechanisms of Radiation Induced Dna Damage: H-Addition to Bases,Direct Ionization and Double Strand Break

Structures and properties of C.(-H) and of TH. were obtained from quantum mechanical calculations. New AMBER parameters for these radicals were obtained to fit their structures and charge distributions. Molecular mechanics simulations of the conformational changes induced in a 12-mer of DNA, d(CGCGAATTCGCG), by these radicals show that the distances between the base and the C₂' of the sugar becomes shorter. Such changes suggest that the base radical can abstract the H,' and transfer the radical from the base to the sugar. Once the radical becomes centered on the sugar a strand break can follow. A simultaneous formation of guanine and thymine radicals on opposite strands may lead to a double strand break.     

Molecular Mechanisms of Radiation Induced Dna Damage: H-Addition to Bases, Direct Ionization and Double Strand Break

Structures and properties of C.(-H) and of TH. were obtained from quantum mechanical calculations. New AMBER parameters for these radicals were obtained to fit their structures and charge distributions. Molecular mechanics simulations of the conformational changes induced in a 12-mer of DNA, d(CGCGAATTCGCG), by these radicals show that the distances between the base and the C₂' of the sugar becomes shorter. Such changes suggest that the base radical can abstract the H,' and transfer the radical from the base to the sugar. Once the radical becomes centered on the sugar a strand break can follow. A simultaneous formation of guanine and thymine radicals on opposite strands may lead to a double strand break.     

6-Amino-8-hydroxy-7,8-dihydro-purine: Radiation Product of Adenine

THERE have been several investigations of the radiation chemistry of DNA and its constituents^1–5 and in this communication I describe the identification of a new major radiation product of adenine.     

Effects of Adenine Derivatives and Auxin-related Compounds on Mitochondrial Membrane Permeability

Adenine derivatives and auxin-related compounds, 2,4-dichlorophenoxyaceticacid (2,4-D) and 2,3,5-triiodobenzoic acid (TIBA), did not inhibitthe transport systems for succinate or malate into mitochondria.In iso-osmotic KC1 medium, some of these compounds increasedion fluxes moderately. TIBA and 2,4-D inhibited the mitochondrialshrinkage induced by the substrates. In contrast, adenine derivativesinhibited only the shrinkage induced by the substrate whoseoxidation they were able to block specifically. (Received February 18, 1987; Accepted June 29, 1987)     

Phosphonylmethyl Analogs of Nucleotides and Their Derivatives: Chemistry and Biology

Abstract

Ribonucleoside O-phosphonylmethyl derivatives are novel isopolar analogs of nucleotides. This review summarizes data on their synthesis and properties, as well as data on novel type of open-chain nucleotide analogs.     

Shape and Volume Changes in Frog Erythrocytes Following Ultraviolet Radiation

Frog erythrocytes in Ringer's solution were exposed to ultraviolet radiation and then followed in camera lucida drawings for changes in shape and dimension. Cell thickness was found to increase while cell width remained constant throughout the period prior to hemolysis. The cell shortened and bulged at the ends during the middle third of the prolytic period while a region around the cell center remained constricted. When this constricted region gave way, the cell became spherical and hemolyzed. Cell volume as calculated from the cell's dimensions increased linearly with time throughout the prolytic period to hemolysis then dropped rapidly to a constant value somewhat higher than the original cell volume. These changes in shape and volume are consistent with a colloid osmotic type of hemolysis but with other factors acting to limit the rate of swelling and the forms assumed during the swelling process. The relationship between the time of hemolysis and the cell surface area exposed to the ultraviolet is discussed as it applies to the site of ultraviolet damage.     

Sites of Adsorption of Adenine,Uracil, and Their Corresponding Derivatives on Sodium Montmorillonite

Clay minerals are considered important to chemical evolution processes due to their properties, ancient origin, and wide distribution. To extend the knowledge of their role in the prebiotic epoch, the adsorption sites of adenine, adenosine, AMP, ADP, ATP, Poly A, uracil, uridine, UMP, UDP, UTP and Poly U on sodium montmorillonite are investigated. X-ray diffraction, ultraviolet and infrared spectroscopy studies indicate that these molecules distribute into the interlamellar channel and the edge of the clay crystals. Monomers are adsorbed predominantly in the interlamellar channel, whereas polymers adsorb along the crystal edges. Such behavior is discussed mainly in terms of bulk pH, pK_a of the adsorbate, and Van der Waals interactions.     

An Antisense Pectin Methylesterase Gene Alters Pectin Chemistry and Soluble Solids in Tomato Fruit

Pectin methylesterase (PME, EC 3.1.11) demethoxylates pectins and is believed to be involved in degradation of pectic cell wall components by polygalacturonase in ripening tomato fruit. We have introduced antisense and sense chimeric PME genes into tomato to elucidate the role of PME in fruit development and ripening. Fruits from transgenic plants expressing high levels of antisense PME RNA showed <10% of wild-type PME enzyme activity and undetectable levels of PME protein and mRNA. Lower PME enzyme activity in fruits from transgenic plants was associated with an increased molecular weight and methylesterification of pectins and decreased levels of total and chelator soluble polyuronides in cell walls. The fruits of transgenic plants also contained higher levels of soluble solids than wild-type fruits. This trait was maintained in subsequent generations and segregated in normal Mendelian fashion with the antisense PME gene. These results indicate that reduction in PME enzyme activity in ripening tomato fruits had a marked influence on fruit pectin metabolism and increased the soluble solids content of fruits, but did not interfere with the ripening process.     

Studies on Radiation Chemistry of Halogenophenols in Aqueous Solution

In relation to the bactericidal action of γ-irradiated halogenophenol solution, radiolysis of p-bromophenol in the aqueous system under anaerobic condition was investigated. Several phenolic compounds could be isolated from the radiolysis products, and three of them were elucidated for their structures. One of them was hydroquinone and the other two were assigned as new asymmetrical dimers, 5-bromo-2,4′-dihydroxybiphenyl and 2-bromo-5,4′-dihydroxybiphenyl, which were confirmed by the syntheses of their methyl ethers.     

Studies on Radiation Chemistry of Halogenophenols in Aqueous Solutions

Among the γ-radiolysis products of p-bromophenol in an aqueous solution, four new oligomers were obtained. By chemical and physical techniques their structures were elucidated as ortho-, meta- and para-terphenyl in which C-4, C-2′ and C-4″ are substituted by hydroxyl groups and C-5′ by a bromine atom and as 5-bromo-2,4′,4″-trihydroxy-m-terphenyl, respectively. These oligomers may be formed by the arylation of p-bromophenol or the dimeric product with an aryl radical intermediate resulted from debromination of p-bromophenol by some radiolysis product(s) of water.     

Direct measurement of superoxide anion produced in biological systems by ESR spectrometry: a pH-jump method

For direct measurement of the ESR signal of superoxide anion (O2-) produced in biological samples, O2- generated at a physiological pH was trapped in alkaline media instead of by a rapid freezing method, and then its signal was measured by ESR spectroscopy at 77 K. A reaction mixture for O2- generation, such as xanthine oxidase-xanthine and neutrophils, was incubated at a physiological pH (pH 7.0-7.5) for a suitable reaction period (30s), then an aliquot (300 microliters) was pipetted out and squirted into 600 microliters of 0.5 M NaOH to stabilize O2- (pH-jump). The alkaline mixture was promptly introduced into an ESR tube and frozen by dipping the tube directly into a cooling liquid. A typical signal of O2- was detected by ESR spectroscopy and the amount of trapped O2- was measured quantitatively at 77 K. The back reaction of O2- generation from H2O2 was negligible in 0.5 M NaOH. To avoid any artificial spectrum due to autoxidation of biological samples by the pH-jump procedure, the background spectrum should be subtracted from the obtained spectrum. This pH-jump method should be widely available for direct demonstration of O2- production in biological systems at physiological pH, because an advantage of this method is the simple operation for trapping O2- without the use of any rapid-mixing apparatus as compared with the rapid freezing method.     

Modelling Direct Radiation and Canopy Gap Regimes in Tropical Forests

Spatial and temporal variation in the below‐canopy light environment of tropical forests is not well known and its measurement is technically challenging. Distributions of gap and understory areas in forests are likewise little known because of the resource requirements of forest structural censuses and a lack of consensus over how gaps should be defined. A basic model of forest structure, based on tree allometries from the 50 ha Forest Dynamics Plot on Barro Colorado Island (BCI), Panama, and a solar positioning algorithm were used to predict spatial and temporal variation in the distribution of direct light at the forest floor. Predicted duration of direct sunlight was then compared with the distribution of gap and understory areas, delimited according to four standard gap definitions, giving predictions for the correspondence between direct light regimes and forest structure. At least 36 percent of the areas of gaps of all sizes was predicted to receive < 1 h of direct sunlight per day, and the understory to receive direct sunlight for ≥ 1 h per day in up to 15 percent of its area, even when not in proximity to gaps. The predicted distribution of light changed over the course of the year with the greatest spread of light throughout the forest floor coinciding with the months when maximum daily solar elevation peaked. These predictions suggest a partial decoupling of light regimes from canopy structure, with implications for gap definitions, patch models of forest development and current understanding of tree seedling recruitment patterns.