Ion-Exchange Chromatography Separates Activities Synthesizing and Degrading Fructose 2,6-Bisphosphate from C3 and C4 Leaves but Not from Rat Liver

Fructose-6-phosphate,2-kinase and fructose-2,6-bisphosphatase were separated on the basis of charge from leaves of C₃ (spinach, lettuce, and pea) and C₄ (sorghum and amaranthus) plants but not from rat liver—a tissue known to contain a bifunctional enzyme with both activities. [2-³²P]Fructose 2,6-bisphosphate binding experiments also suggest that the major forms of these activities reside on different proteins in leaves.     

Role of aminocyclopropane-l-carboxylic acid in ethylene release by distal tissues following localized application of ethephon in Cucurbita pepo

The application of ethephon to a single leaf of Cucurbita pepo L. cv. Trailing Marrow plants caused a huge increase in ethylene production from the treated organ and an increased rate of ethylene production from other parts of the plant. These increases were particularly marked in the shoot apex and expanding leaf. Prior treatment with aminoethoxyvinylglycine (AVG), an ethylene biosynthesis inhibitor, blocked the increased production of ethylene at sites distant from the point of ethephon application. This strongly suggests that the increased ethylene production at these distant sites is due to ethylene biosynthesis and not a result of the translocation of ethylene released by the breakdown of ethephon at the site of application. Assays of 1-aminocyclopropane-l-carboxylic acid (ACC), an ethylene precursor, showed that it increased substantially after ethephon application but was at undetectable levels in the presence of AVG. It is proposed that the application of ethephon stimulates ethylene biosynthesis, but that transport through the plants is effected by ACC which is then converted to ethylene at the shoot apex and leaves.     

Using XAD resins to study the effects of reduced organic micropollutant concentrations in River Rhine and Meuse water on phytoplankton growth

Laboratory incubation experiments were used to study the effect of reduced concentrations of organic micropollutants in water from the rivers Rhine and Meuse on the specific growth rate of the river phytoplankton community. Before incubation, part of the water sampled was treated with XAD-4 and XAD-8 resins to absorb dissolved organic compounds. Four dilutions were made by mixing untreated water with XAD-treated water in the ratios 100:0 (control), 70:30, 40:60 and 0:100. The phytoplankton specific growth rate increased significantly with the increased fraction treated with XAD in all but one incubation experiment. In these experiments, the specific growth rate was on average 9% higher in the fraction in which 100% was treated with XAD than in the controls. In the Rhine and Meuse river water, phytoplankton growth seemed to be inhibited by organic compounds. This inhibition was ascribed to the presence of dissolved organic micropollutants. Removing organic micropollutants using XAD resins to study the toxic effects of these compounds on field phytoplankton communities can be concluded to be a promising tool for risk assessment of micropollutants but needs to be supported by additional methodological research.     

The formation of active hybrid immunoglobulins from the heavy and light chains of beta(1, 6) D-galactan binding murine myeloma IgA's S10 and J539.

Murine myeloma immunoglobulin (IgA, K) J539, which shows enhanced tryptophanyl fluorescence on ligand binding, and S10, which shows reverse-sign changes in tryptophanyl fluorescence on ligand binding (RLIF, see below), have been reduced, alkylated, and dissociated into their light (L) and heavy (H) chains. Two hybrid recombinants, H10L539 and H539L10, have been prepared and the 7S material has been isolated by chromatography. The binding behavior of these recombinants was studied with a number of ligands. Both recombinants showed activity with beta(1 leads to 6) linked galactose ligands comparable to the native immunoglobulins. The ligand-induced fluorescence changes of the recombinants paralleled those of the heavy chain donor. For the recombinant H10L539, two different galactose-ligands caused fluorescence changes in opposite directions. It was quantitatively shown that binding of these ligands, nevertheless, took place in the same combining region. The idiotype of each recombinant resembled that of the heavy chain donor.     

Activation of chloroplast ATPase by reduced thioredoxin

Chloroplast thioredoxin that is reduced by dithiothreitol activates the ATPase that is associated with solubilized preparations of chloroplast coupling factor (CF₁).     

Binding studies on internal immunodeterminants: synthesis of beta-(1----6)-linked oligosaccharide methyl glycosides having one to four internal D-galactopyranosyl residues flanked by gentiobiose residues.

The oligosaccharide glycosides beta-D-Glcp-(1----6)-beta-D-Glcp-(1----6)-[beta-D-Galp-(1----6)]n-beta-D - Glcp-(1----6)-beta-D-Glcp-1----OMe (n = 1-4) were prepared by a convergent block synthesis. Haloacetyl, tert-butyldiphenylsilyl, and dimethylthexylsilyl groups were used as temporary protective groups for the preparation of the intermediate glycosyl donors and acceptors. The deoxygenated trisaccharide glycosides beta-D-Glcp-(1----6)-beta-D-Galp-(1----6)-4-deoxy-beta-D-xylo-Hexp -1----OMe and beta-D-Glcp-(1----6)-4-deoxy-beta-D-xylo-Hexp-(1----6)-beta-D-Galp -1----OMe were also synthesized. The binding of each glycoside to the monoclonal antigalactan antibody IgA J539 was studied and the results support the previous finding that J539 can bind to internal antigenic epitopes. The data are consistent with the interpretation that subsite C of that antibody binds glucose with a Ka of approximately 6 (cf. 10.9 for galactose).