Through-bond correlation of adenine H2 and H8 protons in unlabeled DNA fragments by HMBC spectroscopy

Summary A new application of the HMBC experiment is presented that provides a useful means to discriminate between H2 and H8 proton resonances, to assign the base proton resonances to the various residue types and, most importantly, to correlate the H2 and H8 protons for adenine or inosine residues in natural abundance ¹³C fragments. The utility of this experiment is demonstrated for an unlabeled DNA 20-mer. Thanks to the obtained results, preliminary conclusions could be drawn regarding the molecular conformations of the non-canonical G/I-A base pairs in the hairpin formed by this fragment.     

Preferred conformation of peptides rich in Ac8c,a medium-ring alicyclic Cα,α-disubstituted glycine

A complete series of terminally blocked, monodispersed homo-oligopeptides (to the pentamer level) from the sterically demanding, medium-ring alicyclic C^α,α-disubstituted glycine 1-aminocyclooctane-1-carb oxylic acid (Ac₈c), and two Ala/Ac₈c tripeptides, were synthesized by solution methods and fully characterized. The preferred conformation of all the oligopeptides was determined in deuterochloroform solution by IR absorption and ¹H-NMR. The molecular structures of the amino acid derivative Z-Ac₈c-OH, the dipeptide pBrBz- (Ac₈c)₂-OH and the tripeptide pBrBz-(Ac₈c)₃-OtBu were assessed in the crystal state by X-ray diffraction. Conformational energy computations were performed on the monopeptide Ac-Ac₈c-NHMe. Taken together, the results obtained strongly support the view that the Ac₈c residue is an effective β-turn and helix former. A comparison is also made with the conformational preferences of α-aminoisobutyric acid, the prototype of C^{α, α}-disubstituted glycines, and of the other members of the family of 1-aminocycloalkane-1-carboxylic acids (Ac_nc, with n=3, 5–7) investigated so far. The implications for the use of the Ac₈c residue in peptide conformational design are considered.     

Limits to Catalysis by Ribonuclease A

Bovine pancreatic ribonuclease A (RNase A) catalyzes the cleavage of the P-O(5') bond in RNA. Although this enzyme has been the object of much landmark work in bioorganic chemistry, the nature of its rate-limiting transition state and its catalytic rate enhancement had been unknown. Here, the value of k(cat)/K(m) for the cleavage of UpA by wild-type RNase A was found to be inversely related to the concentration of added glycerol. In contrast, the values of k(cat)/K(m) for the cleavage of UpA by a sluggish mutant of RNase A and the cleavage of the poor substrate UpOC(6)H(4)-p-NO(2) by wild-type RNase A were found to be independent of glycerol concentration. Yet, UpA cleavage by the wild-type and mutant enzymes was found to have the same dependence on sucrose concentration, indicating that catalysis of UpA cleavage by RNase A is limited by desolvation. The rate of UpA cleavage by RNase A is maximal at pH 6.0, where k(cat) = 1.4 × 10(3) s(-1) and k(cat)/K(m) = 2.3 × 10(6) M(-1)s(-1) at 25°C. At pH 6.0 and 25°C, the uncatalyzed rate of [5,6-(3)H]Up[3,5,8-(3)H]A cleavage was found to be k(uncat) = 5 × 10(-9) s(-1) (t(1/2) = 4 years). Thus, RNase A enhances the rate of UpA cleavage by 3 × 10(11)-fold by binding to the transition state for P-O(5') bond cleavage with a dissociation constant of <2 × 10(-15) M.     

Proteinase Inhibitor II Gene Expression Induced by Electrical Stimulation and Control of Photosynthetic Activity in Tomato Plants

Mechanical damage and heat stimulation were used to activateproteinase inhibitor II (Pin2) gene expression in tomato plantsin both treated (local induction) and non-treated tissues (systemicinduction). Both stimuli have been shown to generate electricalsignals, leading to a systemic activation of gene expression.Treatment of tomato leaves with electrical current resultedin the accumulation of Pin2 mRNA in the local and systemic leaves.Additionally, all treatments inducing Pin2 gene activity gaverise to a significant alteration of stomatal aperture. However,heat stimulation provoked a different response in the stomatalparameters than mechanical wounding or electric treatment. Bothmechanical damage and electrical stimulation activated two characteristictime constants in the gas exchange relaxation kinetics. Conversely,heat stimulation resulted in only one major time constant. Theresults clearly show that direct current application to tomatoleaves initiates Pin2 mRNA accumulation locally and systemically.In addition, they suggest the participation of a second slowelectrical/hydraulic component in the wound response mechanismof tomato plants and a possible alternative pathway regulatingheat-induced Pin2 gene expression. (Received February 13, 1995; Accepted April 14, 1995)     

Further farnesyl-homogentisic acid derivatives from Otoba parvifolia

The seeds of Otoba parvifolia contain three novel compounds apparently derived from homogentisic acid, rel-(1′R,5′R)-2-(1′-farnesyl-5′-hydroxy-2′-oxocyclohex-3′-en-1′-yl)-acetic acid and its acetate as well as rel-(1′R,4′S,5′R)-2-(1′-farnesyl-4′,5′-dihydroxy-2′-oxocyclohexan-1′-yl)-acetic acid δ-lactone. The structure of an additional isolate, previously described as 2-(1′-farnesyl-2′-hydroxy-5′-oxocyclohex-3′-en-1′-yl)-acetic acid γ-lactone was revised to rel-(1′R,5′R)-2-(1′-farnesyl-5′-hydroxy-2′-oxocyclohex-3′-en-1′-yl)-acetic acid δ-lactone.     

Root to shoot ratio of crops as influenced by CO2

Crops of tomorrow are likely to grow under higher levels of atmospheric CO₂. Fundamental crop growth processes will be affected and chief among these is carbon allocation. The root to shoot ratio (R:S, defined as dry weight of root biomass divided by dry weight of shoot biomass) depends upon the partitioning of photosynthate which may be influenced by environmental stimuli. Exposure of plant canopies to high CO₂ concentration often stimulates the growth of both shoot and root, but the question remains whether elevated atmospheric CO₂ concentration will affect roots and shoots of crop plants proportionally. Since elevated CO₂ can induce changes in plant structure and function, there may be differences in allocation between root and shoot, at least under some conditions. The effect of elevated atmospheric CO₂ on carbon allocation has yet to be fully elucidated, especially in the context of changing resource availability. Herein we review root to shoot allocation as affected by increased concentrations of atmospheric CO₂ and provide recommendations for further research. Review of the available literature shows substantial variation in R:S response for crop plants. In many cases (59.5%) R:S increased, in a very few (3.0%) remained unchanged, and in others (37.5%) decreased. The explanation for these differences probably resides in crop type, resource supply, and other experimental factors. Efforts to understand allocation under CO₂ enrichment will add substantially to the global change response data base.Abbreviations R:S root to shoot ratio, dry weight basis     

Expression of ferredoxin-dependent glutamate synthase in dark-grown pine seedlings

Pine seedlings are able to accumulate chlorophylls and develop green plastids in a light-independent manner. In this work, we have characterized ferredoxin-dependent glutamate synthase (EC 1.4.7.1; Fd-GOGAT), a key enzyme in nitrogen interconversion during this process. Fd-GOGAT has been purified about 170-fold from cotyledons of maritime pine (Pinus pinaster). As occurs in angiosperms, the native enzyme is a single polypeptide with an apparent molecular mass of 163–168 kDa that is confined to the chloroplast stroma. Polyclonal antibodies generated against the purified enzyme were used to immunoscreen a gt11 expression library from Scots pine (Pinus sylvestris) seedlings and partial cDNA clones were isolated and characterized. The clone with the longest cDNA insert (pGOP44) contained the codification for the C-terminal (550 amino acids) of the pine Fd-GOGAT polypeptide. Immunological cross-reactivity and comparative amino sequence analysis revealed that Fd-GOGAT is a well conserved protein in higher plants. Western blot analyses showed that protein was expressed in chloroplast-containing pine tissues and this expression pattern was not affected by exogenously supplied nitrogen. Fd-GOGAT mRNA, polypeptide and enzyme activity accumulated in substantial amounts in dark-grown pine seedlings. The presence of a functional Fd-GOGAT may be important to provide the required glutamate for the biosynthesis of nitrogen compounds during chloroplast biogenesis in the dark.     

Ionic iridium-gold and rhodium-gold perfluorobenzenethiolato binuclear complexes: syntheses and solution behavior

By reacting [(C₅Me₅)M(SR_F)₂] (forM = Ir, Rf = C₆F₅ (1a) or C₆F₄H-p (1b); for M = Rh, Rf = C₆F₅ (2a) or C₆F₄H-p (2a)) in toluene with Na[AuCl₄], ionic binuclear compounds with the general formula [(C₅Me₅)M(μ-SR_F)₂AuCl₂]Cl for M = Ir, R = C₆F₅ (3a) or C₆F₄H-p (3a); for M = Rh, R_F = C₆F₅ (4a) or C₆F₄H-p (4b) can be obtained, together with small amounts of [(C₅Me₅)₂Rh₂(μ-SR_F)(μ-Cl)₂]Cl (R_F = C₆F₅ (5a) or C₆F₄H-p (5b)) as by-products when 2a and 2b were used.     

Circadian and seasonal variation of the body temperature of sheep in a tropical environment

Nychthemeral and annual rhythms of the rectal temperature were determined for Corriedale sheep in a tropical climate. The minimum rectal temperature averaged 39.55° C at 0500 hours in summer, and 38.87° C at 0600 hours in winter. The maximum was 40.03° C in summer (1700 hours) and 39.33° C in winter (1830 hours). Annual cycle of the rectal temperature showed a minimum in July and maximum in December.