Oxidation of γ-Hydroxybutyrate to Succinic Semialdehyde by a Mitochondrial Pyridine Nucleotide-Independent Enzyme

An antibody that inhibits over 95% of the cytosolic NADP+-dependent gamma-hydroxybutyrate (GHB) dehydrogenase activity of either rat brain or kidney was found to inhibit only approximately 50% of the conversion of [1-14C]GHB to 14CO2 by rat kidney homogenate. A similar result was obtained with sodium valproate, a potent inhibitor of GHB dehydrogenase. The mitochondrial fraction from rat brain and kidney was found to catalyze the conversion of [1-14C]GHB to 14CO2. The dialyzed mitochondrial fraction also catalyzed the oxidation of GHB to succinic semialdehyde (SSA) in a reaction that did not require added NAD+ or NADP+ and which was not inhibited by sodium valproate. The enzyme from the mitochondrial fraction which converts GHB to SSA appears to be distinct from the NADP+-dependent cytosolic oxidoreductase which catalyzes this reaction.     

Subcellular Distribution of UDP-Galactose:Ceramide Galactosyltransferase in Rat Brain Oligodendroglia

Oligodendrocytes isolated from 18-19-day-old rat brain were homogenized in 0.32 M sucrose. The homogenate was centrifuged at 100,000 g for 50 min in a gradient containing 0.8, 1.05, and 1.3 M sucrose. Three discrete bands were obtained at the interfaces 0.32-0.8 (F1), 0.8-1.05 (F2), and 1.05-1.3 M (F3). The distribution of UDP-galactose:ceramide galactosyltransferase (CgalT) activity in each fraction was measured using liposomes containing normal fatty acid-containing ceramides (NFA-CgalT activity) or 2-hydroxy fatty acid-containing ceramides (HFA-CgalT activity). Although detection of both CgalT activities was possible in all fractions, HFA-CgalT activity was enriched in F1 and F2 fractions, which also showed an enrichment of Golgi and endoplasmic reticulum markers, respectively. It is interesting that NFA-CgalT activity was significantly enriched in the F2 fraction. These results suggest that hydroxylated and nonhydroxylated galactocerebrosides may be synthesized at different intracellular locations.     

How can the functional reponse best be determined?

Summary We evaluated three methods for the analysis of functional response data by asking whether a given method could discriminate among functional responses and whether it could accurately identify regions of positive density-dependent predation. We evaluated comparative curve fitting with foraging models, linear least-squares analysis using the angular transformation, and logit analysis. Using data from nature and simulations, we found that the analyses of predation rates with the angular transformation and logit analysis were best at consistently determining the true functional response, i.e. the model used to generate simulated data. These methods also produced the most accurate estimates of the true regions of density dependence. Of these two methods, functional response data best fulfill the assumptions of logit analysis. Angularly transformed predation rates only approximate the assumptions of linear leastsquares analysis for predation rates between 0.1 and 0.9. Lack-of-fit statistics can reveal inadequate fit of a model to a data set where simple regression statistics might erroneously suggest a good match.     

Carbon and nitrogen partitioning in young nodulated pea (wild type and nitrate reductase-deficient mutant) plants exposed to NH4NO3

Carbon and nitrogen partitioning was examined in a wild-type and a nitrate reductase-deficient mutant (A317) of Pisum sativum L. (ev. Juneau), effectively inoculated with two strains of Rhizobium leguminosarum (128C23 and 128C54) and grown hydroponically in medium without nitrogen for 21 days, followed by a further 7 days in medium without and with 5 mM NH₄NO₃. In wild-type symbioses the application of NH₄NO₃ significantly reduced nodule growth, nitrogenase (EC 1.7.99.2) activity, nodule carbohydrates (soluble sugars and starch) and allocation of [¹⁴C]-labelled (NO₃⁻, NH₄⁺, amino acids) in roots. In nodules, there was a decline in amino acids together with an increase in inorganic nitrogen concentration. In contrast, symbioses involving A317 exhibited no change in nitrogenase activity or nodule carbohydrates, and the concentrations of all nitrogenous solutes measured (including asparagine) in roots and nodules were enhanced. Photosynthate allocation to the nodule was reduced in the 128C23 symbiosis. Nitrite accumulation was not detected in any case. These data cannot be wholly explained by either the carbohydrate deprivation hypothesis or the nitrite hypothesis for the inhibition of symbiotic nitrogen fixation by combined nitrogen. Our result with A317 also provided evidence against the hypothesis that NO₃⁻ and NH₄⁺ or its assimilation products exert a direct effect on nitrogenase activity. It is concluded that more than one legume host and Rhizobium strain must be studied before generalizations about Rhizobium /legume interactions are made.     

Structure, Function, and Evolution of Proton-ATPases

Proton-ATPases are among the most important primary ion pumps in nature. There are three classes of these enzymes which are distinguished by their structure, function, mechanism of action, and evolution. They function in ATP formation at the expense of a protonmotive force generated by oxidative and photosynthetic electron transports, maintaining a constant pH in the cytoplasm, and forming acidic spaces in special compartments inside and outside the cell. The three classes of proton-ATPases evolved in a way that prevents functional assembly in the wrong compartment. This was achieved by a triple genetic system located in the nucleus, mitochondria and chloroplast, as well as delicate control of the proton pumping activity of the enzymes.     

Characterization of fructan from mature leaf blades and elongation zones of developing leaf blades of wheat, tall fescue, and timothy

Water-soluble carbohydrate composition of mature (ceased expanding) leaf blades and the elongation zone of developing leaf blades was characterized in wheat (Triticum aestivum L.), tall fescue (Festuca arundinacea Schreb.), and timothy (Phleum pratense L.). These species were chosen because they differ in mean degree of polymerization (DP) of fructan in the mature leaf blade. Our objective was to compare the nature and DP of the fructan. Vegetative plants were grown with a 14-hour photoperiod and constant 21°C at the leaf base. Gel permeation chromatography of leaf blade extracts showed that the apparent mean fructan DP increased in the order wheat < tall fescue < timothy. Apparent mean DP of elongation zone fructan was higher than that of leaf blade fructan in wheat and timothy, but the reverse occurred for tall fescue. Low DP (≤10) and high DP (>10) pools were found in both tissues of tall fescue and wheat, but concentration of low DP fructan was very low in either tissue of timothy. All three species have high DP fructan. Comigration with standards on thin-layer chromotography showed that wheat contained 1-kestose and a noninulin fructan oligomer series. Tall fescue contained neokestose, 1-kestose and higher oligosaccharides that comigrated with neokestose-based compounds and inulins. Thin-layer chromatography showed that small amounts of fructose-containing oligosaccharides were present in timothy.     

Drosophila basement membrane procollagen IV. I. Protein characterization and distribution

A collagen was isolated from Drosophila E85, Schneider line 2L and Kc cell cultures. The purified protein was characterized and antibodies were raised against it. Immunofluorescence microscopy locates this material to the regions of basement membranes of Drosophila embryos, larvae, and adults. The molecules are mostly, or entirely, homotrimers of one polypeptide chain linked by interchain disulfide bonds. The partial amino acid sequences of a cyanogen bromide cleavage product of this chain are identical with a part of the virtual translation product of the Drosophila pro alpha 1(IV) nucleotide sequence that is reported in the accompanying paper. This gene is at Drosophila chromosome location 25C and was identified by the high homology of one part of it with the noncollagenous carboxyl terminus (NC1) of vertebrate type IV basement membrane collagens (Blumberg, B., MacKrell, A. J., Olson, P. F., Kurkinen, M., Monson, J. M., Natzle, J. E., and Fessler, J. H. (1987) J. Biol. Chem. 262, 5947-5950). In the electron microscope each molecule appears as a thread with a knob at one end, which contains the carboxyl peptide domains. The variation of flexibility of the thread was mapped along its length. Pulse-chase labeling of cell cultures showed that these molecules associate into disulfide-linked dimers and higher oligomers that can be partly separated by velocity sedimentation and are resolved by sodium dodecyl sulfate-agarose gel electrophoresis. Dimers and higher oligomers formed by overlap of the amino ends of molecules were found. Mild pepsin digestion of Drosophila embryos and larvae solubilized the corresponding disulfide-linked collagen molecules, and Staphylococcus aureus V8 protease peptide maps showed the identity of the collagen derived from animals and from cell cultures. Individual, native molecules have a sedimentation coefficient s20,w = 4.1 S, the dichroic spectrum and amino acid composition of a collagen, and a Tm = 31 degrees C. Positive in situ hybridization with a specific probe for this collagen began 6-8 h after egg laying and showed message in the locations of embryos and larvae which reacted with the antibodies. This included some prominent individual cells in the hemolymph.