Thermodynamics of heme-induced conformational changes in hemopexin: role of domain-domain interactions.

Hemopexin is a serum glycoprotein that binds heme with high affinity and delivers heme to the liver cells via receptor-mediated endocytosis. A hinge region connects the two non-disulfide-linked domains of hemopexin, a 35-kDa N-terminal domain (domain I) that binds heme, and a 25-kDa C-terminal domain (domain II). Although domain II does not bind heme, it assumes one structural state in apo-hemopexin and another in heme-hemopexin, and this change is important in facilitating the association of heme-hemopexin with its receptor. In order to elucidate the structure and function of hemopexin, it is important to understand how structural information is transmitted to domain II when domain I binds heme. Here we report a study of the protein-protein interactions between domain I and domain II using analytical ultracentrifugation and isothermal titration calorimetry. Sedimentation equilibrium analysis showed that domain I associates with domain II both in the presence and absence of heme with Kd values of 0.8 microM and 55 microM, respectively. The interaction between heme-domain I and domain II has a calorimetric enthalpy of +11 kcal/mol, a heat capacity (delta Cp) of -720 cal/mol.K, and a calculated entropy of +65 cal/mol.K. By varying the temperature of the centrifugation equilibrium runs, a van't Hoff plot with an apparent change in enthalpy (delta H) of -3.6 kcal/mol and change in entropy (delta S) of +8.1 cal/mol.K for the association of apo-domain I with domain II was obtained.(ABSTRACT TRUNCATED AT 250 WORDS)     

An investigation into the solution structure of the single-stranded DNA undecamer 5′d AAGTGTGATAT by means of nuclear Overhauser enhancement measurements

A 500-MHz ¹H-NMR study on the single-stranded DNA undecamer (11-mer) 5d AAGTGTGATAT is presented. Using a combination of one-dimensional pre-steady-state nuclear Overhauser enhancement (NOE) measurements and two-dimensional homonuclear J-correlated spectroscopy, virtually complete resonance assignments are obtained. The relative magnitudes of the intra- and internucleotide NOEs indicate that the overall structure of the single-stranded 11-mer is a right-handed B-type helix with extensive base stacking. Within this overall structure there is quite a large degree of variability, as exemplified by variations in glycosidic bond and sugar pucker conformations, most likely determined by base sequence.Abbreviations NOE nuclear Overhauser effect - COSY twodimensional homonuclear J-correlated spectroscopy - 11-mer undecamer - EDTA sodium ethylenediamine tetraacetate - HPLC nigh-pressure liquid chromatography - DSS 4,4-dimethylsilapentane-1-sulfonate     

Parturition and alate morph determination in the aphid Megoura viciae

In reproducing apterae of Megoura viciae, parturition is often completely arrested during periods of isolation from the host plant. In contrast, surgical removal of the rostrum (including the stylets), amputation of the extremities of the legs, or decapitation, all stimulate parturition away from the plant. These operations also induce alata-producing aphids to revert immediately to the production of apterae, but have no detectable effect on aptera-producers. Carbon dioxide or ether anaesthesia and nitrogen narcosis have a similar action on this maternally controlled response. Although the rostrum and tibio-tarsus bear sensilla whose removal might well be involved in inducing parturition, the influence on morph change is probably indirect and is to a great extent associated with the delay in the resumption of parturition. The effect can be reproduced by isolating individual aphids away from the food plant. The morph change cannot, however, be attributed to starvation since it also occurs when the genital pore of an actively feeding aphid is temporarily occluded. The change in physiology appears to be associated with the retention of embryos at a time when there is no sensory input from crowding.

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Résumé Chez les Megoura viciae aptères, la parturition est souvent complètement arrêtée pendant les périodes de séparation de la plante hôte. Par opposition, l'amputation chirurgicale du rostre (y compris les stylets), de l'extrémité des pattes (tarse et une partie du tibia), ou la décapitation, stimulent toutes la parturition en l'absence de la plante. Les pucerons induits à produire des ailés (élevage antérieur en groupe) retournent, après ces opérations, immédiatement vers la production d'aptères. Le dioxyde de carbone ou l'anesthésie à l'éther et la narcose à l'azote ont une action semblable sur ce déterminisme maternel. Bien que l'élimination des sensilla portées par le rostre et par l'ensemble tarse-tibia puisse être déterminante dans l'induction de la parturition, l'action sur le changement de type semble être principalement associée au retard consécutif dans la reprise de la parturition. Les anesthésiants qui, eux aussi, retardent l'apparition ou la reprise de la parturition, ont probablement une action indirecte du même type.Les pucerons groupés, isolés de la plante hôte pendant plus de 24 h, ont aussi tendance à retourner immédiatement à la production d'aptères. Ce changement de type ne peut, cependant, être attribué au jeûne puisqu'il se produit aussi quand, chez un puceron s'alimentant activement, le pore génital est momentanément bouché. Le changement physiologique semble être associé à la rétention des embryons à un moment où il n'y a pas l'influence sensorielle du groupement.Aucun de ces traitements, à l'exception du groupement, n'induit des pucerons antérieurement isolés à devenir des producteurs d'ailés.

     

Effects of cyanogenesis in bracken fern (Pteridium aquilinum) on associated insects

Abstract. 1. The relationship between cyanogenesis in bracken fern and the insect fauna feeding on the plant was investigated over a 3 year period. The most common insects between May and July, while cyanide levels were high, were the sawflies Strongylogaster impressata Provancher, S.multicincta Norton, Aneug-menus fzavipes (Norton), the aphid Macrosiphum euphorbiae (Thomas) and a microlepidopteran species of Monochroa .
2. Collections of insects from cyanogenic and acyanogenic fronds showed significantly fewer sawflies on the cyanogenic fronds. The aphid and the microlepidopteran were randomly distributed with respect to cyanogenicity.
3. Feeding tests for two of the sawfly species ( Simpressata and Smulticincta ) showed that larvae grew more slowly and had a higher mortality when raised on cyanogenic fronds than on acyanogenic ones.
4. Field collected cyanogenic bracken fronds were found to have sustained less damage from chewing herbivores compared with acyanogenic fronds.     

Esterases of laboratory-reared and field-collected cotton boll weevils,Anthonomus grandis Boh.: Polymorphism of adult esterases and formal genetics of esterase II

The esterases of the cotton boll weevil were separated by polyacrylamide gel electrophoresis into four major regions. These were named Est I–IV in order of migration from anode to origin. Polymorphism was observed in all regions. The Est II region was shown to consist of no more than two bands (fast and slow). The inheritance of the fast and slow bands of Est II was demonstrated to be controlled by codominant autosomal alleles. Analysis of the gene frequency of the Est II region showed that one field population was consistent with the Hardy-Weinberg law (P=0.995), while a second field population was not at equilibrium (P<0.001).This work was supported in part by a Faculty Research Grant from Memphis State University.     

Lipoprotein immunogenetics in primates. I. Two serum beta-lipoprotein allotypes (Lmb1 and Lmb11) in rhesus monkeys and the LP-B immunological relationship with other primates

Immunogenetic investigations on two serum beta-lipoprotein allotypes of rhesus monkeys (Macaca mulatta) are reported. The allotypes, designated Lmb1 and Lmb11, are associated with the main lipoprotein family, LP-B or beta-lipoprotein, expressed on independent beta-molecules, and classify rhesus monkeys into three phenotypes: Lmb1, Lmb11, and Lmb1,11. Genetic and molecular studies indicate that the allotypes are encoded by two codominant autosomal allelic genes, Lmb1 and Lmb11. Anti-Lmb1 cross-reacts with the sera of two other macaque species, whereas anti-Lmb11 with sera of all Old World monkeys. Heteroimmune sera, antihuman apo-B and antirhesus LP-B, showed high but diversified degrees of cross reactivity with other primates.     

Population genetic data on properdin factor B (Bf) in northern Germany.

Properdin factor B phenotypes were determined in 1,112 unrelated individuals and in 151 mother/child combinations from Northern Germany. Gene frequencies were : F = 0.1960, S= 0.7905, F1 = 0.0072, S1 = 0.0063. The data of the mother/child combinations are in full accordance with the postulated gene model.     

Temperature dependence of active K+ transport in cation dimorphic sheep erythrocytes

Arrhenius diagrams of K⁺ pump fluxes measured between 15°C and 41°C were discontinuous in high K⁺ but not in low K⁺ sheep red cells. Exposure of low K⁺ cells to anti-L caused a bimodal temperature response of K⁺ pump flux with a transition temperature, $\text{T}\text{c}$, similar to that found in high K⁺ cells but with comparatively higher activation energies above $\text{T}\text{c}$.     

Reduced color polymorphism in a population of Bunodosoma granulifera

The proportions of carotenoids responsible for column coloration were determined for a population of the sea anemone Bunodosoma granulifera from Grand Cayman using TLC. This population exhibited a very low degree of polymorphism for these proportions, compared to previously sampled populations from Puerto Rico and Curaçao. In addition to the carotenoid pigment system a second system possessing pigments similar to bilins was found for the first time in this genus. This population was also assayed electrophoretically for enzymes encoded by 12 loci. Analysis of these data suggested that the reduced polymorphism for column color may be the result of selection. Although the proportions of carotenoids varied little, the amount of carotenoid per unit of epidermal tissue varied almost four-fold from 0.05 to 0.19 μg/mg dry wt.     

Hemotypes and genetic structure of Camargue horses

The nature and distribution of hemotypes constituted by electrophoretic phenotypes in six loci, in a group of 183 Camargue horses, have been compared with those of five breeds of horses and ponies. The genetic similarities have been observed mainly with New Forest and Haflinger ponies, less with Barbs and Thoroughbreds, and the least with Arab horses.