Reactions between diglycolaldehyde dithioacetals and some nucleophiles

The homogeneous, neutral polysaccharide isolated from the crude polysaccharide of the fruit pulp from bael (Aegle marmelos) contains arabinose, galactose, and glucose in the molar ratios of 2:3:14. The linkages among the different monosaccharide residues were established through methylation analysis and Smith-degradation studies of the polysaccharide. The anomeric configurations of the different glycosyl groups were determined by study of the chromium trioxide oxidation of the acetylated polysaccharide. Results of these experiments have been discussed in order to assess the structure of the neutral polysaccharide.     

Effect of experimental diabetes on glycolytic intermediates and regulation of phosphofructokinase in rat lens

The pattern of glycolytic intermediates in the lens of alloxan-diabetic rats was indicative of regulation at phosphofructokinase. The changes in metabolites influencing phosphofructokinase activity in the diabetic, relative to the normal, rat lens were: glucose 6-phosphate, 182%; fructose 6-phosphate, 107%; fructose diphosphate, 57%. There was also a marked decrease in phosphoenolpyruvate, pyruvate, lactate and ATP but no significant change in other triose phosphates or cyclic AMP. The resuts are considered in relation to the early changes in [Ca²⁺] known to occur in lens in diabetes and to the coordinating effect of fructose diphosphate on flux through the glycolytic route.     

Intracellular (Golgi) receptors for insulinlike peptides in rat liver

An insulinlike peptide (ILAs) has been isolated in our laboratory from human serum. The binding of 123I-labeled ILAs was studied in subcellular fractions from rat liver and found to be much greater in microsomes than purified plasmalemma. The high level of microsomal binding was due to a particular enrichment of binding sites in Golgi elements. Binding to Golgi was time and temperature dependent and was augmented by an increase of either subcellular fraction or 125I-labeled ILAs in accordance with a mass action process. Degradation of 125I-labeled ILAs was greatest in the Golgi vesicle fraction and was reduced by incubation at 4 degrees C. Bound 125I-labeled ILAs could be eluted and was found to retain integrity. Binding was pH dependent with a broad optimum at pH 7.7-8.5. Dissociation of bound 125I-labeled ILAs was time and temperature dependent. It was greater at 37 than 4 degrees C, and was uninfluenced by unlabeled ILAs. The ILAs receptor was stable at 4 degrees C but was markedly decreased by preincubation at 37 degrees C. The binding of 125I-labeled ILAs was inhibited by unlabeled ILAs and related insulinlike peptides (the insulinlike growth factors, IGF-1 and IGF-2) in a dose-dependent manner. Insulin and its analogues had only a partially inhibitory effect, and structurally unrelated peptides were without inhibitory efficacy. In contrast ILAs and IGF-1 and IGF-2 inhibited 125I-labeled insulin binding to its receptors in a dose-dependent fashion. These observations identify a receptor for insulinlike peptides in the Golgi elements of rat liver. It is distinct from the insulin receptor previously observed in these elements. The dual interaction of ILAs and other insulinlike peptides with both the insulin receptor and their own unique receptor constitutes the presumed biochemical basis for the two types of action effected by this family of peptides, namely, an effect on metabolism comparable to insulin and an effect on cellular anabolism and growth.     

Species specificity and intraspecific variation in the chemical profiles of Heliconius butterflies across a large geographic range

In many animals, mate choice is important for the maintenance of reproductive isolation between species. Traits important for mate choice and behavioral isolation are predicted to be under strong stabilizing selection within species; however, such traits can also exhibit variation at the population level driven by neutral and adaptive evolutionary processes. Here, we describe patterns of divergence among androconial and genital chemical profiles at inter‐ and intraspecific levels in mimetic Heliconius butterflies. Most variation in chemical bouquets was found between species, but there were also quantitative differences at the population level. We found a strong correlation between interspecific chemical and genetic divergence, but this correlation varied in intraspecific comparisons. We identified “indicator” compounds characteristic of particular species that included compounds already known to elicit a behavioral response, suggesting an approach for identification of candidate compounds for future behavioral studies in novel systems. Overall, the strong signal of species identity suggests a role for these compounds in species recognition, but with additional potentially neutral variation at the population level.     

Improving the phenotype predictions of a yeast genome‐scale metabolic model by incorporating enzymatic constraints

Genome‐scale metabolic models (GEMs) are widely used to calculate metabolic phenotypes. They rely on defining a set of constraints, the most common of which is that the production of metabolites and/or growth are limited by the carbon source uptake rate. However, enzyme abundances and kinetics, which act as limitations on metabolic fluxes, are not taken into account. Here, we present GECKO, a method that enhances a GEM to account for enzymes as part of reactions, thereby ensuring that each metabolic flux does not exceed its maximum capacity, equal to the product of the enzyme's abundance and turnover number. We applied GECKO to a Saccharomyces cerevisiae GEM and demonstrated that the new model could correctly describe phenotypes that the previous model could not, particularly under high enzymatic pressure conditions, such as yeast growing on different carbon sources in excess, coping with stress, or overexpressing a specific pathway. GECKO also allows to directly integrate quantitative proteomics data; by doing so, we significantly reduced flux variability of the model, in over 60% of metabolic reactions. Additionally, the model gives insight into the distribution of enzyme usage between and within metabolic pathways. The developed method and model are expected to increase the use of model‐based design in metabolic engineering.     

Invasive cane toads are unique in shape but overlap in ecological niche compared to Australian native frogs

Invasive species are an important issue worldwide but predicting invasiveness, and the underlying mechanisms that cause it, is difficult. There are several primary hypotheses to explain invasion success. Two main hypothesis based on niche spaces stand out as alternative, although not exclusive. The empty niche hypothesis states that invaders occupy a vacant niche space in the recipient community, and the niche competition hypothesis states that invaders overlap with native species in niche space. Studies on trait similarity/dissimilarity between the invader and native species can provide information on their niche overlap. Here, we use the highly invasive and well‐studied cane toad (Rhinella marina) to test these two hypotheses in Australia, and assess its degree of overlap with native species in several niche dimensions. We compare extensive morphological and environmental data of this successful invader to 235 species (97%) of native Australian frogs. Our study is the first to document the significant morphological differences between the invasive cane toad and a continent‐wide frog radiation: despite significant environmental overlap, cane toads were distinct in body size and shape from most Australian frog species, suggesting that in addition to their previously documented phenotypic plasticity and wide environmental and trophic niche breadth, their unique shape also may have contributed to their success as an invasive species in Australia. Thus, the invasive success of cane toads in Australia may be explained through them successfully colonizing an empty niche among Australian anurans. Our results support that the cane toad's distinct morphology may have played a unique role in the invasiveness of this species in Australia, which coupled with a broad environmental niche breadth, would have boosted their ability to expand their distribution across Australia. We also propose RLLR (Relative limb length ratio) as a potentially useful measure of identifying morphological niche uniqueness and a potential measure of invasiveness potential in anuran amphibians.