Modeling the Role of Negative Cooperativity in Metabolic Regulation and Homeostasis

A significant proportion of enzymes display cooperativity in binding ligand molecules, and such effects have an important impact on metabolic regulation. This is easiest to understand in the case of positive cooperativity. Sharp responses to changes in metabolite concentrations can allow organisms to better respond to environmental changes and maintain metabolic homeostasis. However, despite the fact that negative cooperativity is almost as common as positive, it has been harder to imagine what advantages it provides. Here we use computational models to explore the utility of negative cooperativity in one particular context: that of an inhibitor binding to an enzyme. We identify several factors which may contribute, and show that acting together they can make negative cooperativity advantageous.     

Abiotic edaphic factors affecting the growth of a threatened North American Sunflower, Helianthus paradoxus (Asteraceae)

This study evaluated the relationships among soil moisture, soil salinity, and soil oxygen on the growth of Helianthus paradoxus (Asteraceae), a threatened inland salt marsh species of western North America. The study was conducted in large growth boxes (1×2×0.3 m) tilted at an angle to achieve a saturated to dry water gradient similar to that found in the marsh. This experimental design allowed the evaluation of major abiotic factors (soil moisture and soil salinity) which have been shown to be potentially important for this species, while removing major biotic factors, such as competition from other community dominants. Maximum aboveground biomass occurred in the middle rows of the boxes, where surface soil water was reduced and subsurface soil water was intermediate in the gradient. Regression analyses indicated that H. paradoxus would grow best where surface soil water is approximately 5%, subsurface soil water ranges from 20 to 30%, and where surface soil salinity is less than 0.5 g kg⁻¹. Edaphic variables, particularly soil moisture and soil salinity, affect the growth of H. paradoxus. Data presented here suggest that the survival of this species depends on maintenance of the hydrologic regime.     

Conformations of blood group H-active oligosaccharides of ovarian cyst mucins

Spectroscopic data and conformational energy calculations are reported for eight oligosaccharides from ovarian cyst mucins and from human milk, the nonreducing terminals of which have fucose (α1 → 2)galactose linked either (β1 → 3) (type I) or (β1 → 4)(type II) to N-acetylglucosamine or in (β1 → 3) linkage to galactosaminitol. The fully assigned proton nmr spectra are reported along with nuclear Overhauser enhancement (NOE) data. Amide proton coupling constants and vacuum-uv CD spectra provide information on the amide plane orientation and amide environment. Our results imply that the fucosidic dihedral angles are similar for all three cases and that the substantial differences in the chemical shifts of the fucosyl protons of type I, type II, and 3-ol chains result from different perturbations by the amide group of the residue to which the β-galactose is linked. Stereopair diagrams of conformational models for both type I and II H chains are presented that are consistent with NOE, coupling constants, conformational energy calculations, and the CD data. While the temperature dependence of the observed NOE of penta- and hexasaccharides indicates that their rotational correlation times are strongly temperature dependent, we conclude that the conformations are essentially independent of temperature.     

Darting and marking techniques for an arboreal forest monkey,Cercopithecus ascanius

Techniques are described for capturing and marking redtail monkeys (Cercopithecus ascanius). An air-powered darting rifle and syringe darts loaded with a Ketamine-Rompun mixture were used for capture. Ketamine was used for maintaining anesthesia. Monkeys were darted 48 times and captured 27 times. In 24 of the 27 captures, the monkeys were released unharmed. Adult males were marked with radiotransmitters attached to collars of nylon webbing. Females received nylon webbing collars with colorcoded plastic washers for identification.     

Comparison by 1H-nmr spectroscopy of the conformation of the 2600 dalton antifreeze glycopeptide of polar cod with that of the high molecular weight antifreeze glycoprotein

The antifreeze glycopeptide (AFGP-8) from polar cod, B. saida, is a 14-amino acid polypeptide having alternating glycotripeptide sequences of Ala-[Gal(β1 → 3)GalNAc(β1 → O)]-Thr-Pro and Ala-[Gal(β1 → 3)GalNAc(β1 → O)]-Thr-Ala, with alanyl residues at amino and carboxy terminals. Conformational studies of AFGP-8 have been carried out by ¹H-nmr and empirical energy calculations to investigate the difference in its antifreeze behavior from that of the more active high-molecular weight AFGP 1-4 of P. borchgrevinki. The ¹H-nmr spectra, including the resonances of the exchangeable amide protons, were assigned by two-dimensional correlated spectroscopy (COSY), one-dimensional difference decoupling, and nuclear Overhauser effect (NOE) measurements. For the four threonyl residues, the amide proton coupling constants and the small coupling constants between H^α and H^β indicate similar conformations, despite significant chemical shift differences. The strong NOE between the α protons and the amide protons of the residue following together with large temperature coefficients of chemical shifts, indicate an extended conformation not consisting of α-helix, turns or bends. Energy computations indicate several low-energy conformations consistent with the observed coupling constants for ?. Among these, a left-handed helical conformation with three repeating residues per turn has been proposed, which is in accordance with the observed NOE between the methyl group of the α-GalNAc and Ala H^βs. While the observed Overhauser effects in the threonyl side chain suggest a certain amount of conformational averaging, the effect involving the acetmido methyl of α-GalNAc and H^βs of Ala indicate that it as is a major conformer. In view of the close similarity between the conformations of AFGP-8 and the more active antifreeze polymer, AFGP 1-4, we propose that the difference in their activities is due to the length of the regular repeating structure with glycosylation at every third amino acid residue, and not due to any fundamental difference in their conformations.     

Determination of the absolute configuration of the sugar residues of complex polysaccharides by circular dichroism spectroscopy

Circular dichroism spectroscopy is used to determine the absolute configuration of the constituent sugar residues of bacterial polysaccharides from two strains of Streptococcus sanguis which are important receptors in bacterial coaggregation in the formation of dental plaque. A high-pressure liquid chromatographic method for carbohydrate analysis of glycoproteins, glycolipids, and polysaccharides has been extended to sugar chirality determination by collection of the eluted HPLC fractions and subsequent measurement of their circular dichroism spectra. The method involves methanolysis of the polysaccharide followed by formation of O-benzoyl derivatives and HPLC on reverse-phase columns. Circular dichroism spectra of the collected derivatives in acetonitrile solution in the region 230 nm show large ellipticity bands resulting from "chiral exciton" interaction among the O-benzoyl chromophores which are sensitive to the orientation of hydroxyl groups in the parent sugars. The sensitivity of the method is in the submicrogram range for the absolute configuration of single sugar residues. The circular dichroism of the intact polysaccharide in aqueous solution shows CD bands from the amide chromophore in the region 180 to 220 nm which are sensitive to the chirality of 2-acetamido sugar residues.     

Reproductive physiology of the clouded leopard: II. A circannual analysis of adrenal-pituitary-testicular relationships during electroejaculation or after an adrenocorticotropin hormone challenge

A circannual analysis was made of serum cortisol, luteinizing hormone (LH), and testosterone concentrations in the male clouded leopard (Neofelis nebulosa). Group I males (n = 4), maintained in a standardized environment, were bled serially during a regimented anesthesia/electroejaculation episode occurring monthly (beginning in January, ending in December). Additional sampling intervals were conducted under anesthesia only (control, n = 8), anesthesia plus a single adrenocorticotropin hormone challenge (ACTH, Cortrosyn, n = 4), or anesthesia plus a single 25 micrograms injection of gonadotropin-releasing hormone (GnRH, Gonadorelin, n = 4). Group II males (n = 6) from various zoological collections were sampled serially under the same semen collection conditions on one random occasion within the year. Serum cortisol levels were 2 times greater than values measured in comparable studies involving other felid species. Cortisol concentrations were similar during electroejaculation and control (anesthesia only) episodes, and mean levels did not rise as a result of semen collection. Adrenocorticotropin caused an immediate rise in cortisol to levels at least 1.5 times greater than electroejaculated or control counterparts. Mean concentrations of basal cortisol in individual males gradually increased as the year progressed, possibly as a consequence of repeated psychogenic stress. Between seasons, there were no differences in mean LH; however, testosterone levels were greater (p less than 0.05) in the winter compared to all other seasons. There were no differences (p greater than 0.05) between individual males in secretory patterns or mean concentrations of cortisol, LH, or testosterone. Within males, distinct temporal fluctuations were observed in both LH and testosterone during the approximately 80-min sampling interval. Neither LH nor testosterone profiles appeared affected by cortisol patterns during electroejaculation or after an ACTH challenge. A bolus of GnRH induced a marked rise in serum LH and testosterone within 15 and 30 min respectively, indicating that these two hormones were coupled. Both LH and testosterone profiles in Group II males mimicked those in Group I; concentrations of cortisol in Group II males immobilized on one occasion were similar to those of Group I animals sampled from January-May but appeared to be less than values measured from June-December. These data demonstrate that the clouded leopard, compared to other felids, produces markedly elevated concentrations of cortisol, which are likely related to an aggressive behavioral temperament.(ABSTRACT TRUNCATED AT 400 WORDS)     

Thymus-independent immunogenicity in vitro of the divalent antigen DNP-polyethylene oxide

Chemically simple and physically well-defined dinitrophenyl derivatives of polyethylene oxide (DNP-PEO) can be prepared in a wide range of forms and sizes. These materials were used to investigate the molecular basis of immunogenicity and the binding of the antigens to membrane-bound receptors. Both di- and multivalent DNP-PEO activate normal murine B lymphocytes to yield primary anti-DNP antibody response in vitro. The immunogenicity is dependent on the carrier chain length but independent of T cells. Responses comparable to those induced by DNP-conjugated polymerized flagellin are induced by divalent linear materials of medium molecular weights of about 60,000. A highly multivalent material is moderately immunogenic, but at much lower antigen doses than divalent materials. The carrier PEO does not affect B-cell responses to DNP-PEO or T-cell response to succinyl concanavalin A. Moreover, it shows no polyclonal mitogenicity at concentrations as high as 1 mg/ml. Studies of antigen binding to cell surface DNP receptors show that the strongly immunogenic materials of medium molecular weights have an appreciable tendency to bind bivalently and thus potentially to crosslink receptors. The binding of smaller, less immunogenic antigen appears predominantly monovalent.