Structure of Leu5-enkephalin bound to a model membrane as determined by high-resolution NMR

Summary Opioid peptides are thought to interact with the cell membrane in their biological journey to the membrane-bound receptor. Both organic solvents and model membranes have been used previously to determine the stable solution conformations of peptide hormones. Leucine enkephalin has been studied in a number of different environments, but with limited resolution. Here it is shown that leucine enkephalin forms a stable type IV -turn structure in dodecylphosphocholine micelles. We have observed a highly solvent-shielded amide proton with no evidence for a complementary hydrogen bond acceptor. The structural details of the peptide as determined by NMR spectroscopy in solution are described.     

Thermoregulation and metabolism in the Cape golden mole (Insectivora: Chrysochloris asiatica)

The Cape golden mole, Chrysochloris asiatica is an insectivore which excavates superficial foraging burrows as it searches for its food. It has a mean (±S.D.) resting metabolic rate (RMR) when newly captured of 1–17±0.17 cm³ O₂g^-1 h^-1 ( n = 14), within the thermoneutral zone (TNZ) of 30–32°C.
The body temperature (Tb) of the mole in the TNZ is low 32.9 ± 0.36 ( n = 14) and remains stable at ambient temperatures (Tas) from 28–32°C. Above 32°C (range 34–37°C), Tb increases albeit slightly to 36 ± 1.75°C ( n = 14). The conductance is high 0.27 ± 006cm³ O₂g^-1 h^-l°C^-1 ( n = 46) at the lower limit of thermoneutrality. The mean RMR at 9°C (the lowest Ta tested) was 4.82±11 cm³ O₂g^-1h^-1, which is 4.1 times that of the RMR in the TNZ.
At an ambient temperature of 9°C, three of the golden moles entered a state of torpor where the RMR was reduced from 5.9±0.56 to 10 1.0 ± 0.69cm³O₂g^-1h^-1.     

Coefficients of digestibility and nutritional values of geophytes and tubers eaten by southern African mole-rats (Rodentia: Bathyergidae)

Subterranean rodents have high energy requirements when they are excavating their burrows. This study investigates the energy available to, and the efficiency with which it can be extracted by, four species of bathyergid mole-rats fed natural diets ranging from the underground storage organs of geophytes to grass roots and leaves.
The digestibility coefficients of geophytes ranged from 53% for the fibrous tuber of the gemsbok cucumber to 95–7% for corms and bulbs. One species, Bathyergus suillus whose diet consists of over 80% grass, had a digestibility coefficient of 87% on an all grass diet.
All species had similar coefficients of digestibility of > 90% when fed on a uniform diet of sweet potato.
Bulbs and corms had a low fibre content (3–3–4%), high calorific value (15–16kJ/g) and high digestibility coefficients (95–7–96%) and on this diet the mole-rats maintained their body mass. Food of lower digestibility tended to have a high fibre content (8–2–45%) and, with the exception of B. suillus , although the mole-rats consumed a greater quantity of food, they lost mass. The sweet potato had a low fibre content (4–1 %) but was energetically very similar to bulbs and corms (15–5 kJ/g).
Geophytes which have low fibre contents are generally small (1–20 g), whereas geophytes with high fibre contents are much larger (30–2000 g) and often occur in more arid zones.     

Pre- and post-maturation survival in adults of the damselfly Pyrrhosoma nymphula (Zygoptera: Coenagrionidae)

The technique of mark-release-recapture was used to study survival before and after sexual maturity in adults of the damselfly Pyrrhosoma nymphula (Sulzer). Fewer females were recaptured upon return to water to breed despite no differences in dispersal or daily survival rate between the sexes over the immature period. Because females took longer to mature than males, their poorer recapture rate was attributed to greater overall mortality during their longer maturation phase. Survivorship curves for tenerals marked at emergence suggested that overall survival of immature adults was similar to, if not better than, that of mature adults. The reasons for this are discussed.
Jolly's model was used to estimate daily survival rates for mature adults. The assumptions of the model were tested rigorously. Estimates for females were statistically less reliable than those for males. Mean reproductive spans for males and females were 6.8 and 6.6 days, respectively, giving mean total adult lifespans of 19.4 days and 21.6 days for individuals surviving the maturation period.
Because neither sex visited the breeding site every day, sampling exclusively at water resulted in underestimation of mean reproductive spans for both sexes. Female reproductive spans were underestimated to a greater extent; because females remain away from water longer between visits, there is a greater chance that they will die before being recaptured.
Mean reproductive spans were also underestimated when only a sub-section of the habitat was sampled. Females were significantly more mobile than males and this increased the likelihood that they would move out of the study area, resulting in more severe underestimation. The importance of obtaining accurate estimates of mature lifespan for females is discussed.     

Gating of gap junction channels.

Gap junctional conductance ( gj ) in various species is gated by voltage and intracellular pH (pHi). In amphibian embryos, gj is reduced to half by a 14 mV transjunctional voltage ( Vj ), a change that in fish embryo requires approximately 28 mV. Crayfish septate axon and pairs of dissociated rat myocytes show no voltage dependence of gj over a range of Vj greater than +/- 50 mV. In fish and amphibian blastomeres , gj is steeply decreased by decrease in pHi (n, Hill coefficient: 4.5) and the apparent pKH (7.3) is in the physiological range. In crayfish septate axon the pKH is lower (6.7) and the curve is less steep (n = 2.7). Rises in cytoplasmic Ca can also decrease gj but much higher concentrations are required (greater than 0.1 mM in fish blastomeres). Voltage and pH gates on gap junctions in amphibian embryos appear independent. In squid blastomeres pH gates exhibit some sensitivity to potential, both transjunctional and between inside and outside. A pharmacology of gap junctions is being developed: certain agents block gj directly (aldehydes, alcohols, NEM in crayfish); others block by decreasing pHi (esters that are hydrolyzed by intrinsic esterases, NEM in vertebrates, and, as in the experiments demonstrating the effect of pHi, weak acids). Certain agents block pH sensitivity without affecting voltage dependence (retinoic acid, glutaraldehyde, EEDQ), further indicating separateness of pH and voltage gates. These studies demonstrate a dynamics of gap junctional conductance and variability in gating in a series of possibly homologous membrane channels.     

Differentiation of fiber types in wing muscles during embryonic development: effect of neural tube removal

The embryonic precursors of the avian slow (type I and III) and fast (type II) fibers can be distinguished from each other early in muscle formation (stage 28, V. Hamburger and H. L. Hamilton, J. Morphol, 88, 49-92, 1951) on the basis of the differential sensitivity of their myosin ATPases. To test the neural dependence of fiber type differentiation, the source of motor innervation was eliminated by excision of the brachial neural tube at stages 16-18 before muscles are innervated. Removal of the brachial neural tube did not affect the number of primary myotubes in a sample muscle of the forelimb (ulnimetacarpalis dorsalis, UMD) up until stage 36. Myosin ATPase staining at a variety of pHs revealed the typical patterns of fiber types in muscles of neural-tube free embryos in stages 35-37. These muscles included the anterior latissimus dorsi, brachialis, and UMD which showed presumptive type III staining (type IIIEMB), the pronator superficialis and flexor carpi ulnaris which showed embryonic type II staining (type IIEMB), and the triceps brachii muscles which showed characteristic arrangements of both type IEMB and type IIEMB fibers. The normal patterns of type IEMB and type IIEMB myotubes were also seen in muscles containing a heterogeneous mixture of fiber types such as the biceps brachii, extensor metacarpi radialis, and adductor indicis muscles, although the intensity of acid-stable ATPase staining of the type IEMB myotubes in these muscles was lower than in innervated muscles. It is concluded that the earliest differentiation of muscle fiber types is independent of the nervous system.     

Schistosoma mansoni: differences in acetylcholine, dopamine, and serotonin control of circular and longitudinal parasite muscles

The physiological and pharmacological properties of circular and longitudinal somatic musculature in adult male Schistosoma mansoni were compared using cut muscle sections. Carbachol reduced tone in both circular and longitudinal muscle, but was without effect on circular muscle bathed in high Mg2+, indicating that cholinergic receptors were not associated with circular muscle membrane. 5-Hydroxytryptamine (5-HT) induced rhythmic contractile activity in both sets of muscle. It decreased muscle tone in circular muscle but increased the tone of longitudinal muscle. Metergoline blocked 5-HT effects on both sets of muscle. 5-HT continued to be effective on both sets of muscle bathed in high-Mg2+ medium, indicating that serotonergic receptors were present on both circular and longitudinal muscle membranes. Dopamine decreased both circular and longitudinal muscle tone. Its effects on circular muscle were still present after exposure to high Mg2+, but its effects on the longitudinal muscle were significantly reduced, leading to the conclusion that dopaminergic sites were probably associated with circular muscle membrane but not that of longitudinal muscle. Also, spiroperidol blocked stimulus responsiveness of the circular muscle but not that of the longitudinal muscle. From these studies it appears that there are significant physiological and pharmacological differences between circular and longitudinal muscles in the adult male schistosome.     

Concentrations of sucrose and nitrogenous compounds in the apoplast of developing soybean seed coats and embryos

The apoplast of developing soybean (Glycine max cv Hodgson) embryos and seed coats was analyzed for sucrose, amino acids, ureides, nitrate, and ammonia. The apoplast concentration of amino acids and nitrate peaked during the most rapid stage of seed filling and declined sharply as the seed attained its maximum dry weight. Amino acids and nitrate accounted for 80 to 95% of the total nitrogen, with allantoin and allantoic acid either absent or present in only very small amounts. Aspartate, asparagine, glutamate, glutamine, serine, alanine, and γ-aminobutyric acid were the major amino acids, accounting for over 70% of the total amino acids present. There was a nearly quantitative conversion of glutamine to glutamate between the seed coat and embryo, most likely resulting from the activity of glutamate synthase found to be present in the seed coat tissue. This processing of glutamine suggests a partly symplastic route for solutes moving from the site of phloem unloading in the seed coat to the embryo.