Dynamic and structural properties of glucose oxidase enzyme

The catalytic oxidation of β-D-glucose by the enzyme glucose oxidase involves a redox change of the flavin coenzyme. The structure and the dynamics of the two extreme glucose oxidase forms were studied by using infrared absorption spectroscopy of the amide I′ band, tryptophan fluorescence quenching and hydrogen isotopic exchange. The conversion of FAD to FADH₂ does not change the amount of α-helix present in the protein outer shell, but reorganises a fraction of random coil to β-sheet structure. The dynamics of the protein interior vary with the redox states of the flavin without affecting the motions of the structural elements near the protein surface. From the structure of glucose oxidase given by X-ray crystallography, these results suggest that the dynamics of the interface between the two monomers are involved in the catalytic mechanism. Received: 27 December 1996 / Accepted: 18 July 1997     

Effects of an increase in summer precipitation on leaf, soil, and ecosystem fluxes of CO2 and H2O in a sotol grassland in Big Bend National Park, Texas

Global climate models predict that in the next century precipitation in desert regions of the USA will increase, which is anticipated to affect biosphere/atmosphere exchanges of both CO₂ and H₂O. In a sotol grassland ecosystem in the Chihuahuan Desert at Big Bend National Park, we measured the response of leaf-level fluxes of CO₂ and H₂O 1 day before and up to 7 days after three supplemental precipitation pulses in the summer (June, July, and August 2004). In addition, the responses of leaf, soil, and ecosystem fluxes of CO₂ and H₂O to these precipitation pulses were also evaluated in September, 1 month after the final seasonal supplemental watering event. We found that plant carbon fixation responded positively to supplemental precipitation throughout the summer. Both shrubs and grasses in watered plots had increased rates of photosynthesis following pulses in June and July. In September, only grasses in watered plots had higher rates of photosynthesis than plants in the control plots. Soil respiration decreased in supplementally watered plots at the end of the summer. Due to these increased rates of photosynthesis in grasses and decreased rates of daytime soil respiration, watered ecosystems were a sink for carbon in September, assimilating on average 31 mmol CO₂ m⁻² s⁻¹ ground area day⁻¹. As a result of a 25% increase in summer precipitation, watered plots fixed eightfold more CO₂ during a 24-h period than control plots. In June and July, there were greater rates of transpiration for both grasses and shrubs in the watered plots. In September, similar rates of transpiration and soil water evaporation led to no observed treatment differences in ecosystem evapotranspiration, even though grasses transpired significantly more than shrubs. In summary, greater amounts of summer precipitation may lead to short-term increased carbon uptake by this sotol grassland ecosystem.     

The roles of hyperglycaemia and oxidative stress in the rise and collapse of the natural protective mechanism against vascular endothelial cell dysfunction in diabetes

Vascular endothelial cell (VEC) dysfunction in diabetes has been associated with hyperglycaemia-induced intra- and extracellular glycation of proteins and to overproduction of glucose-derived free radicals. VEC protect their intracellular environment against an increased influx of glucose in face of hyperglycaemia by reducing the expression and plasma membrane abundance of their glucose transporter-1 (GLUT-1). We investigated the hypothesis that glucose-derived free radicals induce this down-regulatory mechanism in VEC, but proved the contrary. In fact, pro-oxidants significantly increased the expression and plasma membrane abundance of GLUT-1 and the rate of glucose transport in VEC while abolishing high-glucose-induced down-regulation of the hexose transport system. The resulting uncontrolled influx of glucose followed by overproduction of glucose-derived ROS further up-regulates the rate of glucose transport, and vice versa. This perpetuating glycoxidative stress finally leads to the collapse of the auto-regulatory protective mechanism and accelerates the development of dysfunctional endothelium in blood vessels.     

Reproductive Conflict and Division of Labor in Eutetramorium mocquerysi, a Myrmicine Ant Without Morphologically Distinct Female Reproductives

The myrmicine ant Eutetramorium mocquerysi Emery from Madagascar exhibits a unique social organization. All female individuals are similar in size and appearance; female reproductives with a distinct external morphology do not exist. Based on ovarian anatomy, however, two major types of females can be distinguished: females with six ovarioles and a spermatheca, which can mate and produce diploid offspring, and females with only two ovarioles, which lack a spermatheca but can lay unfertilized eggs. Individuals with three to five ovarioles are rare. Anatomical differences are not correlated with different roles. Both types of females were observed foraging, tending brood, and laying eggs. However, only females with six ovarioles and a spermatheca were the reproductively and socially most dominant individuals. Nestmate antagonism, which for the first time is demonstrated for an ant species belonging neither to the Ponerinae nor the Formicoxenini, consists of biting, antennation bouts, and ritualized dominance postures. In two colonies, removal of the dominant individual resulted in the destruction of all larvae and pupae.     

Airway cellularity, lipid laden macrophages and microbiology of gastric juice and airways in children with reflux oesophagitis

Background and methods

Human metapneumovirus (hMPV) is a recently discovered respiratory virus associated with bronchiolitis, pneumonia, croup and exacerbations of asthma. Since respiratory viruses are frequently detected in patients with acute exacerbations of COPD (AE-COPD) it was our aim to investigate the frequency of hMPV detection in a prospective cohort of hospitalized patients with AE-COPD compared to patients with stable COPD and to smokers without by means of quantitative real-time RT-PCR.

Results

We analysed nasal lavage and induced sputum of 130 patients with AE-COPD, 65 patients with stable COPD and 34 smokers without COPD. HMPV was detected in 3/130 (2.3%) AE-COPD patients with a mean of 6.5 × 10⁵ viral copies/ml in nasal lavage and 1.88 × 10⁵ viral copies/ml in induced sputum. It was not found in patients with stable COPD or smokers without COPD.

Conclusion

HMPV is only found in a very small number of patients with AE-COPD. However it should be considered as a further possible viral trigger of AE-COPD because asymptomatic carriage is unlikely.     

Accelerated triacylglycerol turnover kinetics in hearts of diabetic rats include evidence for compartmented lipid storage

Triacylglycerol (TAG) storage and turnover rates in the intact, beating rat heart were determined for the first time using dynamic mode (13)C- NMR spectroscopy to elucidate profound differences between hearts from diabetic rats (DR, streptozotocin treatment) and normal rats (NR). The incorporation of [2,4,6,8,10,12,14,16-(13)C(8)]palmitate into the TAG pool was monitored in isolated hearts perfused with physiological (0.5 mM palmitate, 5 mM glucose) and elevated substrate levels (1.2 mM palmitate, 11 mM glucose) characteristic of the diabetic condition. Surprisingly, although the normal hearts were enriched at a near-linear profile for >or=2 h before exponential characterization, exponential enrichment of TAG in diabetic hearts reached steady state after only 45 min. Consequently, TAG turnover rate was determined by fitting an exponential model to enrichment data rather than conventional two-point linear analysis. In the high-substrate group, both turnover rate (DR 820+/- 330, NR 190 +/-150 nmol.min(-1).g(-1) dry wt; P< 0.001) and [TAG] content (DR 78 +/-10, NR 32+/- 4 micromol/g dry wt; P< 0.001) were greater in the diabetic group. At lower substrate concentrations, turnover was greater in diabetics (DR 530+/-300, NR 160+/- 30; P<0.05). However, this could not be explained by simple mass action, because [TAG] content was similar between groups [DR 34+/- 7, NR 39+/- 9 micromol/g dry wt; not significant (NS)]. Consistent with exponential enrichment data, (13)C fractional enrichment of TAG was lower in diabetics (low- substrate groups: DR 4+/-1%, NR 10+/- 4%, P<0.05; high-substrate groups: DR 8+/- 3%, NR 14+/- 9%, NS), thereby supporting earlier speculation that TAG is compartmentalized in the diabetic heart.     

La grotte de Niaux,théâtre des illusions

Niaux Cavern, one of the great decorated caves, has been continuously open to the public. Despite its apparent accessibility, there is much that remains beyond our comprehension. One of the most inaccessible images is in the much visited Salon Noir. It is panel number four which contains a powerful but puzzling figure sometimes referred to as the Crossed Bison. This paper is an attempt to reach into the mind of the individual who produced that image to show how that artist's evident understanding of optical illusions, as well as an intuitive understanding of the theory of mind, propelled its creation for a specific graphic purpose.