Diadenosine triphosphate splitting by rat liver extracts.

A splitting activity on diadenosine triphosphate has been found in rat liver. One of the products of the cleavage is ADP. A Km of 10 μM has been found. This activity on diadenosine triphosphate seems to be specific as diadenosine tetraphosphate, a nucleotide previously described by others to occur in rat liver at very low concentration, is not a substrate of the reaction. The occurrence of diadenosine triphosphate in rat liver has not been so far reported, but a dinucleoside triphosphate structure has been described at the 5′ end of certain mRNAs. The possibility that this enzymatic activity may be involved in the hydrolysis of diadenosine triphosphate or in the processing of mRNAs is suggested.     

Properties of spinach chloroplast fructose-1,6-diphosphatase

Photosynthetic fructose-1,6-diphosphatase (FDPase) fractions I and II, earlier purified from spinach leaves, show a similar amino acid composition, with the exception of a higher glutamic acid content in the latter. In both fractions glutamic and aspartic acids are the main amino acids. pH activity profiles of fractions I and II are similar, with optima at 8·65–8·70, both showing a high specificity for fructose- 1,6-diphosphate. These two fractions are Mg²⁺-dependent for activity, with an Optimum Mg²⁺ concentration of 10 mM in standard conditions, which shifts to 5 mM when the MG²⁺/EDTA ratio is increased to 10; Mn²⁺ and Co²⁺ are slightly active. EDTA enhances FDPase activity slightly, with an optimum at 0·4–0·8 mM. Cysteine has no activating effect, and acts as an inhibitor above 10 mM. Both I and II have an optimum substrate concentration of 4 mM, and the substrate inhibits at concns above this value. Kinetic velocity curves are sigmoidal, with the concave zone located in the range of physiological substrate concns. (Hill coefficient 1·75 for both). This suggests a strong regulatory role of fructose-1,6-diphosphate. K_m values are 1·4 × 10⁻³ M (fraction I) and 1·1 × 10⁻³ M (fraction II). The highest activity rate occurs at 60°, in accordance with the high thermostability of both fractions; the activation energies are 14·3 kcal/mol (fraction I) and 13·0 kcal/mol (fraction II).     

Interaction of ethidium bromide with the transport system for monovalent cations in yeast

Summary Ethidium was found to be taken up by yeast cells in a process that, at certain concentrations has the main following characteristics: a) a substrate is required; b) it presents cooperative kinetics, withn, according to the Hill equation 3; c) ethidium can be concentrated more than 100-fold; d) the uptake is inhibited by Ca²⁺; e) the uptake of the dye is inhibited by monovalent cations with a selectivity pattern similar to that observed in their transport by yeast; f) ethidium inhibits the uptake of K⁺, and, at concentrations up to about 250 m produces a competitive inhibition on the uptake of Rb⁺; and g) ethidium produces the same effects as K⁺ on respiration and the extrusion of H⁺. It is concluded that ethidium is taken up by yeast cells in a selective way by the same transport system normally employed for monovalent cation uptake.     

Neutral currents in weak interactions and molecular asymmetry

Weak interactions are parity violating forces, i.e. they differentiate between mirror images. Therefore it is a very attractive hypothesis to invoke weak interactions in explaining the origin of molecular asymmetry. It is, however, not clear whether weak interactions may operate between electrons and/or between electrons and protons? For these types of interactions so called neutral currents are needed. Recent experiments with muon neutrinos at CERN gave some evidence for the existence of neutral currents. Thus we may suppose that parity violating forces are active in molecules. In the first part of this paper a very elementary theory of weak interactions is outlined with special reference to the discovery of neutral currents. In the second part we show how weak interactions may differentiate between mirror image molecules. The asymmetrically distributed static charges in chiral molecules represent a helical potential field. This potential field may exert an effect on the orbital electrons and therefore coupling of spins and momenta occurs. Thus the enantiomers are parity transformed images not only as geometrical bodies, but their orbital electrons are parity transformed too as "a helical electron gas". Weak interactions will differentiate between L and D forms because their orbital electrons have a nonzero spin polarization with respect to their velocity.     

On the possible role of organic melanoidin polymers as matrices for prebiotic activity

Summary One of the major diagenetic pathways of organic matter in recent sediments involves the condensation of cellular constituents, particularly amino acids and sugars, into insoluble melanoidin-type polymers. These polymers consist mainly of humic and fulvic acids and make up the major part of the organic carbon reservoir in recent sediments. We suggest that a similar set of reactions between abiotically formed amino acids and sugars, and more generally between aldehydes and amines, occurred on a large scale in the prebiotic hydrosphere. The rapid formation of this insoluble polymeric material would have removed the bulk of the dissolved organic carbon from the primitive oceans and would thus have prevented the formation of an "organic soup".Melanoidin polymers have several properties which make them attractive hypothetical precursors of contemporary oxidation-reduction coenzymes: 1. they contain heterocyclic nitrogen compounds similar to the nitrogenous bases; 2. they contain a high concentration of stable free radicals; and 3. they tend to concentrate those heavy metals which play prominent roles in contemporary enzymic redox processes. The prebiotic formation of similar polymers could, therefore, have provided the starting point for a basic class of biochemical reactions.We suggest that the prebiotic scenario involved chemical and protoenzymic reactions at the sediment-ocean interface in relatively shallow waters and under conditions not much different from those of the recent environment.On leave from the Isotope Department, Weizmann Institute of Sciences, Rehovot, Israel. This is the address for reprint requests.On leave from the Department of Cell and Molecular Biology, San Francisco State University, San Francisco, California.On leave from the Department of Biophysics, University of Houston, Houston, Texas.     

New germacranolides from Liatris species

Three closely related cis-Δ⁴-diepoxygermacranolides were isolated from two Liatris species. Structures of eleganin from L. elegans (Walt.) Michx, and liscundin and liscunditrin from L. secunda (Ell.) Small. were established by NMR spectrometry, chemical transformations and correlation with punctaliatrin previously isolated from L. punctata Hook. Reinvestigation of the latter species yielded another germacranolide liatripunctin whose structure is reported.     

Microbial oxidation of elemental sulphur in brown soil

Plant and Soil - Brown soil formed from loamy clay was examined for its ability to produce sulphate from added elemental suphur. At higher rates of sulphur applications the pH of a slightly acid...