Exogenous fibronectin modifies the aggregation of collagen-stimulated human platelets

Summary Fibronectins (FN) are adhesive glycoproteins whose role in platelet aggregation is unclear. Addition of 3, 6 and 12 g/ml of human plasma FN in vitro to isolated human platelets, which had been freed from plasma FN by gel filtration and subsequently stimulated with collagen, inhibited the last stage of platelet aggregation. With 3 and 6g/ml of FN a shortening of the lag-time was also observed. These data showed that FN may play a role in platelet-collagen interaction as well as in platelet-platelet interaction.     

Nitric oxide-related pancreatic endocrine responses to hyperglycaemia in the conscious calf

Mean plasma insulin concentration was reduced and mean plasma glucose concentration increased following the administration of N-nitro-L-arginine methyl ester (L-NAME; 100 mol kg^–1 i.a.) in conscious calves given continuous infusions of exogenous glucose (30–60 mol min^–1 kg^–1 i.v.). It is concluded that the rise in plasma insulin concentration which occurs in these animals in response to glucose is mediated, at least in part, by a nitric oxide-related factor (NOx).     

<Emphasis Type="Italic">Naja siamensis</Emphasis>, a cryptic species of venomous snake revealed by mtDNA sequencing

Because of possible variation in venom composition, an understanding of venomous snake systematics is of great importance for the optimization of antivenom treatment of snakebite patients. Intraspecific variation in the morphology of many venomous snakes complicates the definition and indentification of some species when allopatric populations are involved. Selectively neutral or near-neutral mtDNA sequences can reveal evolutionary relationships obscured by ecogenetically-caused morphological variation. We use comparative sequencing of the cytochrome oxidase subunit 1 gene to reveal the existence of a widespread, cryptic species of spiting cobra from southeast Asia. This species,Naja siamensis, is widely sympatric with other Asiatic cobra species. This may be of considerable medical significance, and calls for further research into venom composition in Asiatic cobras.     

Variability of sterol utilization in stored-products insects

A comparison of sterol utilization by 3 stored-products insects revealed very different capabilities. The fluor beetle,Tribolium castaneum dealkylates and converts dietary sitosterol to about equal amounts of cholesterol (43.7%) and 7-dehydrocholeterol (39.8%), whereas another flour beetle,Tenebrio molitor, produces considerably less 7-dehydrocholesterol (16.8%) and relatively more cholesterol (66.7%) from sitosterol. The lepidopteran,Plodia interpunctella, utilized dietary sterol very similar to plant-feeding lepidoptera, producing primarily cholesterol (86.5%) from sitosterol.     

Induction of cyst formation by low temperature in the dinoflagellate<Emphasis Type="Italic">Gonyaulax polyedra</Emphasis> Stein: Dependence on circadian phase and requirement of light

Encystment, which at a temperature of 15°C is photoperiodically controlled inGonyaulax polyedra, can also be induced by a decrease of temperature, from 20 to 10 or 8°C in the absence of photoperiodic signals. The cyst-inducing capacity of the decrease in temperature depends on the circadian phase: in constant light, the maximum of sensitivity was found at the beginning of subjective night. In a light/dark cycle, however, cyst formation was reduced during dark phase, indicating that light is required for the process of encystment. A similar light dependence was seen in the effect of the physiologically occurring cyst inducer 5-methoxytryptamine, but not in the encystment response to the protonophores monensin and nigericin.     

Thrombospondin co-localises with TGFβ and IGF-I in the extracellular matrix of human osteoblast-like cells and is modulated by 17β estradiol

Thrombospondin (TSP) is a multifunctional glycoprotein which is synthesised by several cell types including osteoblasts, and incorporated into the extracellular matrix (ECM) of these cells. The function and regulation of TSP in bone is not clear. In this study, using a long term culture model of human osteoblast-like cells, we examined the distribution of TSP in the ECM and its modulation by added estradiol. In this model the osteoblast-like cells form a regular multilayer which continues to increase in depth up to 50 days post confluence. In the ECM of these cultures and in 19-week fetal bone, the bone markers osteocalcin and alkaline phosphatase were diffusely distributed in the matrix. In contrast, labelling for TSP was concentrated, confined to the banded collagen and its immediately adjacent ECM. This pattern of labelling resembled that of the growth factors transforming growth factor-I (TGF), and insulin-like growth factor-I (IGF-I), with which TSP label co-localised. Labelling intensities were comparable between fetal bone and the in vitro material for TSP, TGF and IGF-I. TSP label was present by 10 days post confluence, reached a maximum by 20 days, and declined slowly thereafter, a time course which was similar to that of IGF-I. Incubation of osteoblast-like cell cultures with 17 estradiol resulted in an increase in multilayer depth and a maximal 3-fold increase in TSP labeling at 30 days as well as approximately 2-fold increases for TGF and IGF-I. The dose-response relationship for these responses to estradiol treatment was biphasic with maximal increases at 10^–10 M–10^–11 M of added estradiol. Treatment with 17 estradiol produced labelling intensities that were not significantly different from controls. Studies with other cell types have suggested that TSP may be involved in modulation of growth factor activity. The similarities between TSP, TGF and IGF-I, in terms of their distribution and regulation by 17 estradiol treatment, may indicate a role for TSP in modulating bone cell proliferation and function through interaction with local growth factors.     

Atmospheric carbon dioxide concentrations before 2.2 billion years ago

The composition of the Earth's early atmosphere is a subject of continuing debate. In particular, it has been suggested that elevated concentrations of atmospheric carbon dioxide would have been necessary to maintain normal surface temperatures in the face of lower solar luminosity in early Earth history. Fossil weathering profiles, known as palaeosols, have provided semi-quantitative constraints on atmospheric oxygen partial pressure (pO2) before 2.2 Gyr ago. Here we use the same well studied palaeosols to constrain atmospheric pCO2 between 2.75 and 2.2 Gyr ago. The observation that iron lost from the tops of these profiles was reprecipitated lower down as iron silicate minerals, rather than as iron carbonate, indicates that atmospheric pCO2 must have been less than 10(-1.4) atm--about 100 times today's level of 360 p.p.m., and at least five times lower than that required in one-dimensional climate models to compensate for lower solar luminosity at 2.75 Gyr. Our results suggest that either the Earth's early climate was much more sensitive to increases in pCO2 than has been thought, or that one or more greenhouse gases other than CO2 contributed significantly to the atmosphere's radiative balance during the late Archaean and early Proterozoic eons.     

Kinetic model for the smectite to illite transformation in active geothermal systems

The smectite to illite transformation in active geothermal systems of New Zealand can be simulated by a first-order reaction kinetic model, which provides direct estimates about the minumum ages of active geothermal systems themselves. The derived kinetic values show that the smectite to illite transformation is sensitive to both temperature and time.     

超滤法分级和纯化蛋白质的现状和前景(英文)

超滤法具有高产率、低成本、容易放大等显著优点,但其低选择性一直限制其在生物蛋白制品的分级和纯化中的应用。本文总结和分析了超滤法用于蛋白质分级和纯化的近期研究成果,对其低选择性的原因进行了分析,提出并论证了提高超滤选择性的技术途径。