Ingenol esters from the pro-inflammatory fraction of Euphorbia kamerunica

A series of unstable mono- and di-esters of the tetracyclic diterpene ingenol were isolated from the pro-inflammatory ether-soluble fraction of the latex of Euphorbia kamerunica. The esters were isolated by a neutral process involving column and thin-layer chromatography. The monoesters were identified by spectroscopic methods and hydrolysis reactions as ingenol-3-decanoate, ingenol-3-dodecanoate, ingenol-5-hexadienoate and ingenol-5-octenoate and the diesters as 20-acetyl-ingenol-3-octenoate and 20-acetyl-ingenol-3-angelate.     

Investigation of the H(2) Oxidation System in Rhizobium japonicum 122 DES Nodule Bacteroids

The H₂-oxidizing complex in Rhizobium japonicum 122 DES bacteroids failed to catalyze, at a measurable rate, ²H¹H exchange from a mixture of ²H₂ and ¹H₂ in presence of ²H₂O and ¹H₂O, providing no evidence for reversibility of the hydrogenase reaction in vivo. In the H₂ oxidation reaction, there was no significant discrimination between ²H₂ and ¹H₂, indicating that the initial H₂-activation step in the over-all H₂ oxidation reaction is not rate-limiting. By use of improved methods, an apparent K_m for H₂ of 0.05 micromolar was determined. The H₂ oxidation reaction in bacteroids was strongly inhibited by cyanide (88% at 0.05 millimolar), theonyltrifluoroacetone, and other metal-complexing agents. Carbonyl cyanide m-chlorophenylhydrazone at 0.005 millimolar and 2,4-dinitrophenol at 0.5 millimolar inhibited H₂ oxidation and stimulated O₂ uptake. This and other evidence suggest the involvement of cytochromes and nonheme iron proteins in the pathway of electron transport from H₂ to O₂. Partial pressures of H₂ at 0.03 atmosphere and below had a pronounced inhibitory effect on endogenous respiration by bacteroid suspensions. The inhibition of CO₂ evolution by low partial pressures of H₂ suggests that H₂ utilization may result in conservation of oxidizable substrates and benefits the symbiosis under physiological conditions. Succinate, acetate, and formate at concentrations of 50 millimolar inhibited rates of H₂ uptake by 8, 29, and 25%, respectively. The inhibition by succinate was noncompetitive and that by acetate and formate was uncompetitive. A concentration of 11.6 millimolar CO₂ (initial concentration) in solution inhibited H₂ uptake by bacteroid suspensions by 18%. Further research is necessary to establish the significance of the inhibition of H₂ uptake by succinate, acetate, formate, and CO₂ in the metabolism of the H₂-uptake-positive strains of Rhizobium.     

Auxin action on proton influx in corn roots and its correlation with growth

At concentrations inhibitory to the elongation of corn (Zea mays L.) roots, the auxins, indole-3-acetic acid (IAA) and α-naphthaleneacetic acid (α-NAA), cause an increase in the pH of the bathing medium; this increase occurs with an average latent period shorter than the latent period for the inhibitory effect of these auxins on elongation. Indole-2-carboxylic acid, an inactive structural analogue of IAA, and β-naphthaleneacetic acid, an inactive analogue of α-NAA, affect neither growth nor the pH of the medium. Since acid pH is known to promote and basic pH to inhibit root elongation, the data are consistent with the hypothesis that hormone-induced modification of cell-wall pH plays a role in the control of elongation of roots, as has been proposed for elongation of stems and coleoptiles.     

Biphasic effect of acute ethanol administration on rat liver tyrosine-2-oxoglutarate aminotransferase activity.

1. Acute ethanol administration causes a biphasic change in rat liver tyrosine aminotransferase activity. 2. The initial decrease is significant with a 200 mg/kg dose of ethanol, is prevented by adrenoceptor-blocking agnets and by reserpine, but not by inhibitors of ethanol metabolism, and exhibits many of the characteristics of the inhibition caused by noradrenaline. 3. The subsequent enhancement of the enzyme activity by ethanol is not associated with stabilization of the enzyme, but is sensitive to actinomycin D and cycloheximide. 4. It is suggested that the initial decrease in aminotransferase activity is caused by the release of catecholamines, whereas the subsequent enhancement may be related to the release of glucocorticoids.     

Stabilization of rat liver tyrosine aminotransferase in vivo by pyridoxine administration.

Administration of pyridoxine stabilizes rat liver tyrosine aminotransferase in vivo, whereas administration of cortisol, cyclic AMP, glucagon, insulin, tryptophan or tyrosine does not. The results of these and other experiments with pyridoxine are discussed in relation to the mechanisms of action of this vitamin on the activity of the enzyme.     

The electrophoresis of transferrins in urea/polyacrylamide gels.

The denaturation of transferrin by urea has been studied by (a) electrophoresis in polyacrylamide gels incorporating a urea gradient, (b) measurements of the loss of iron-binding capacity and (c) u.v. difference spectrometry. In human serum transferrin and hen ovotransferrin the N-terminal and C-terminal domains of the iron-free protein were found to denature at different urea concentrations.     

Chiasma distribution in mouse oocytes during diakinesis

The distribution of chiasmata in the mouse was examined by measurement of a single metacentric bivalent in 173 oocytes taken from 36 mice of the Rb3Bnr stock. Frequency distribution analysis revealed a well defined pattern of chiasma formation in both arms of the metacentric and, as in other organisms, interference and localization were thought to be major factors influencing this pattern. Despite the tendency for bivalents to form terminal associations at metaphase in the mouse and reported differences in chiasma frequency between early and late stages of meiosis, analysis of bivalents at diakinesis has produced no quantitative support for the concept of terminalization of chiasmata during meiosis.     

Analysis of adhesion of large vesicles to surfaces.

An experimental procedure that can be used to measure the interfacial free energy density for the adhesion of membranes of large vesicles to other surfaces is outlined and analyzed. The approach can be used for both large phospholipid bilayer vesicles and red blood cells when the membrane force resultants are dominated by isotropic tension. The large vesicle or red cell is aspirated by a micropipet with sufficient suction pressure to form a spherical segment outside the pipet. The vesicle is then brought into close proximity of the surface to be tested and, the suction pressure reduced to permit adhesion, and the new equilibrium configuration is established. The mechanical analysis of the equilibrium shape provides the interfacial free energy density for the surface affinity. With this approach, the measurable range of membrane surface affinity is 10(-4)-3 erg/cm2 for large phospholipid bilayer vesicles and 10(-2)-10 erg/cm2 for red blood cells.     

NADH binding to porcine mitochondrial malate dehydrogenase.

The binding of NADH to porcine mitochondrial malate dehydrogenase in phosphate buffer at pH 7.5 has been studied by equilibrium and kinetic methods. Hyperbolic binding was obtained by fluorimetric titration of enzyme with NADH, in the presence or absence of hydroxymalonate. Identical results were obtained for titrations of NADH with enzyme in the presence or absence of hydroxymalonate, measured either by fluorescence emission intensity or by the product of intensity and anisotropy. The equilibrium constant for NADH dissociation was 3.8 +/- 0.2 micrometers, over a 23-fold range of enzyme concentration, and the value in the presence of saturating hydroxymalonate was 0.33 +/- 0.02 micrometer over a 10-fold range of enzyme concentration. The rate constant for NADH binding to the enzyme in the presence of hydroxymalonate was 3.6 X 10(7) M-1 s-1, while the value for dissociation from the ternary complex was 30 +/- 1 s-1. No limiting binding rate was obtained at pseudo-first order rate constants as high as 200 s-1, and the rate curve for dissociation was a single exponential for at least 98% of the amplitude. In addition to demonstrating that the binding sites are independent and indistinguishable, the absence of effects of enzyme concentration on the KD value indicates that NADH binds with equal affinity to monomeric and dimeric enzyme forms.