Degradation of aromatic amino acids by Rhodococcus erythropolis

A Gram-positive Rhodococcus erythropolis strain S1 was shown to assimilate aromatic amino acids such as L-phenylalanine, L-tyrosine, L-tryptophan, D-phenylalanine, D-tyrosine and D-tryptophan, which were utilized not only as the sole carbon source but also as a suitable nitrogen source. The highest growth on these aromatic amino acids occurred at a temperature of 30°C. L-Phenylalanine, L-tyrosine and L-tryptophan degradative pathways would appear to be independent, and to be induced alternatively. The strain S1 also showed the ability to assimilate peptides which consisted of only L-phenylalanine and L-tyrosine.     

Inhibition of leukocyte adhesion by the in vivo and in vitro administration of cannabinoids

Cannabinoids have been shown to affect various aspects of arachidonic acid metabolism both in vivo and in vitro. Eicosanoid metabolites of arachidonate and related octadecanoate are believed to be involved in cell adhesion processes as agonists in some instances and as antagonists in other cases. This report shows data in which cannabinoids exhibit marked inhibitory effects on the adhesion of mouse peritoneal cells to polystyrene culture dishes. The effects could be seen by in vivo administration of the drugs as well as by direct exposure of the cells in vitro. The data suggest that this inhibition of adhesion is mediated by one or more products generated by stimulation of a lipoxygenase pathway.     

A survey of cultivated heirloom tomato varieties identifies four new mutant alleles at the green-flesh locus

The process of crop domestication occurs through the selection and subsequent propagation of novel alleles that improve traits of interest. Cultivated tomato (Solanum lycopersicum), particularly heirloom varieties, exhibit a wide range of variation in fruit size, shape and color. The green-flesh mutant of tomato possesses a stay-green phenotype resulting in fruits that ripen to a red-brown color, due to the retention of chlorophyll and the simultaneous accumulation of lycopene. The recent identification of the GREEN-FLESH gene provides a molecular tool with which to investigate the origin of a subset of cultivated tomato varieties that resemble the green-flesh mutant. Sequence analysis of the GF locus from 26 varieties revealed the existence of four previously unidentified null alleles. This study illustrates the potential of cultivated tomato varieties, including heritage cultivars, heirlooms, and land races, for uncovering new alleles in genes of interest.     

Macrophage catabolism of lipid A is regulated by endotoxin stimulation

Lipopolysaccharide (LPS) is a Gram-negative bacterial glycolipid that is believed to cause, by virtue of its stimulatory actions on macrophages and other eukaryotic cells, the life-threatening symptoms associated with Gram-negative infections. Macrophages both respond to and catabolically deactivate LPS. The lipid A moiety of LPS is responsible for the stimulatory actions of LPS on macrophages. We have previously developed methods employing a radiolabeled bioactive lipid A precursor, 4'-32P-lipid IVA, to study the interaction of this class of lipids with animal cells (Hampton, R. Y., Golenbock, D. T., and Raetz, C. R. H. (1988). J. Biol. Chem. 263, 14802-14807). In the current work, we have examined the uptake and catabolism of 4'-32P-lipid IVA by the RAW 264.7 cell line in serum-containing medium at physiological temperatures and have studied the effect of LPS stimulation on the ability of these cells to catabolize lipid IVA. RAW 264.7 macrophage-like cells avidly take up 4'-32P-lipid IVA under cell culture conditions at nanomolar concentrations. Uptake of lipid IVA was accompanied by lysosomal dephosphorylation of a fraction of the lipid to yield 4'-monophosphoryl lipid IVA. Chemically generated 4'-monophosphoryl lipid IVA was found to be substantially less bioactive than lipid IVA in the RAW cell, indicating that this catabolic dephosphorylation results in detoxification. In uptake experiments of 3-4 h duration, all metabolism of lipid IVA is blocked by ligands of the macrophage scavenger receptor. In longer experiments (24 h), both scavenger receptor-dependent and -independent uptake are responsible for the lysosomal catabolism of lipid IVA. Preincubation of RAW 264.7 cells with LPS caused dose-dependent inhibition of lipid IVA dephosphorylation. Sufficient LPS stimulation resulted in essentially complete inhibition of lipid IVA catabolism in both short- and long-term uptake experiments. This effect occurred at physiologically relevant concentrations of LPS (IC50 less than 1 ng/ml), and our data indicate that LPS-induced blockade of lipid IVA catabolism was due to the resultant physiological stimulation of the cells, and not inhibition of dephosphorylation by competition for uptake or enzymatic sites or by simple sequestration of labeled lipid IVA by LPS aggregates. We suggest that in the macrophage, LPS can modulate its own catabolism by virtue of its pharmacological properties. This effect of LPS could play a role in LPS pathophysiology as well as in macrophage biology.     

Determination of products of acetohydroxy acid synthase by the colorimetric method, revisited

The enzyme acetohydroxy acid synthase (AHAS, EC 4.1.3.18) catalyzes two competing reactions of physiological importance: condensation of two molecules of pyruvate to form acetolactate (AL) or condensation of pyruvate and 2-ketobutyrate to form acetohydroxybutyrate (AHB). The activity of AHAS is most frequently analyzed using the Westerfeld method, in which the acetoin formed upon decarboxylation of AL is determined by colorimetric reaction with creatine and alpha-naphthol. However, there has been confusion as to the interpretation of the results of this assay in the presence of both substrates, conditions which lead to formation of both AL and AHB. By applying this assay to enzymatically prepared samples of AL and AHB which have also been analyzed by two other independent methods, we show here that the color yield for AHB in the commonly used assay is 35-40% that for equivalent amounts of acetoin or AL. The relative color yield is not significantly affected by varying the time or temperature of various steps in the color-forming reaction. This information could in principle be used, together with an independent specific assay for AHB, to determine the composition of an AHAS product mixture; it would, however, be less accurate than a simultaneous chromatographic method.     

Assignment of a human serum glycoprotein SP-40,40 gene (CLI) to chromosome 8.

SP-40,40 is a serum glycoprotein consisting of two different subunits (alpha and beta) assembled into a dimer by disulfide bonds. Northern blot hybridization, using total RNA from several cell lines, showed that SP-40,40 is expressed in glioblastoma and testicular tumor cells, as well as hepatoma cells. Spot blot hybridization of flow-sorted human chromosomes, using a SP-40,40 cDNA fragment as a probe, localized the gene for SP-40,40 to human chromosome 8. This gene has been given the designation CLI, for complement lysis inhibitor, by the Human Gene Nomenclature Committee.     

Global patterns of diversity among the specialist birds of riverine landscapes

1. Despite the growing view that biodiversity provides a unifying theme in river ecology, global perspectives on richness in riverine landscapes are limited. As a result, there is little theory or quantitative data on features that might have influenced global patterns in riverine richness, nor are there clear indications of which riverine landscapes are important to conservation at the global scale. As conspicuous elements of the vertebrate fauna of riverine landscapes, we mapped the global distributions of all of the world's specialist riverine birds and assessed their richness in relation to latitude, altitude, primary productivity and geomorphological complexity (surface configuration). 2. Specialist riverine birds, typical of high‐energy riverine landscapes and dependent wholly or partly on production from river ecosystems, occur in 16 families. They are represented by an estimated 60 species divided equally between the passerines and non‐passerines. Major radiation has occurred among different families on different continents, indicating that birds have evolved several times into the niches provided by riverine landscapes. 3. Continental richness varies from four species in Europe to 28 in Asia, with richness on the latter continent disproportionately larger than would be expected from a random distribution with respect to land area. Richness is greatest in mountainous regions at latitudes of 20–40°N in the riverine landscapes of the Himalayan mountains, where 13 species overlap in range. 4. Family, genus and species richness in specialist riverine birds all increase significantly with productivity and surface configuration (i.e. relief). However, family richness was the best single predictor of the numbers of species or genera. In keeping with the effect of surface configuration, river‐bird richness peaks globally at 1300–1400 m altitude, and most species occur typically on small, fast rivers where they feed predominantly on invertebrates. Increased lengths of such streams in areas of high relief and rainfall might have been responsible for species–area effects. 5. We propose the hypothesis that the diversity in channel forms and habitats in riverine landscapes, in addition to high temperature and primary productivity, have been prerequisites to the development of global patterns in the richness of specialist riverine organisms. We advocate tests of this hypothesis in other taxonomic groups. We draw attention, however, to the challenges of categorically defining riverine organisms in such tests because (i) rivers grade into many other habitat types across several different ecotones and (ii) `terrestrialisation' processes in riverine landscapes means that they offer habitat for organisms whose evolutionary origins are not exclusively riverine.     

The effects of thiamine inhibition on ruminal fermentation: a preliminary study

Inhibition of methanogenesis in ruminal cultures was attempted by hindering thiamine availability through its degradation by ‘polyphenols’ and competition for active sites on enzymes and transporters using thiamine structural analogs. Effects on fermentation were small and not consistently reversed by adding thiamine. Lack of major effects of the compounds evaluated could be due to intracellular synthesis of thiamine covering most requirements.