Pathways for alanine transport in intestinal basal lateral membrane vesicles

Summary Membrane vesicles obtained from the basal lateral membranes of the rat intestinal epithelium were used to study the pathways for neutral amino acid transport.In the absence of sodium there was a stereospecific uptake ofl-alanine which exhibited saturation kinetics (K _m 0.73mm andV _max 5.3 nmol/mg min at 22°C). The activation energy for this process was 8.1 kcal/mole between 5 and 25°C. Preloading the vesicles with alanine increased the unidirectional influx of alanine into the vesicle. Competition experiments indicated that the affinity of the sodium-independent transport system was glutamine > threonine > alanine > phenylalanine > valine > methionine > glycine > histidine > proline, N-MeAIB. These are the characteristics of the classical L transport system.External sodium increased the rate of the stereospecificl-alanine uptake. The Na-dependent flux had aK _m of 0.04mm and aV _max of 0.26 nmol/mg min at 22°, and an activation energy of 9.1 kcal/mole between 5 and 25°C. Competition experiments suggest the existence of three separate pathways for alanine transport in the presence of sodium. A major pathway is shared by all other amino acids tested (i.e., threonine, glutamine, methionine, phenylalanine, valine, proline and N-MeAIB). This resembles the classical A system. A second pathway is unavailable to either phenylalanine or N-MeAIB; this is reminiscent of the classical ASC system; and the third is a novel pathway which is shared by N-MeAIB but not phenylalanine.The sodium-independent and the sodium-dependent transport ofl-alanine was blocked by PCMBS and significantly inhibited by DTP and NEM. It is concluded that the sodium-independent system (the L-like system) accounts for the efflux of neutral amino acids from the epithelium to the blood during the absorption of amino acids from the gut, and that the sodium-dependent transport processes may play an important role in the supply of amino acids to the epithelium in the absence of amino acids from the gut lumen.     

Regional and subcellular distribution of cysteine sulfinate transaminase in rat nervous system

The distribution of the cysteine sulfinate transaminase activity in adult and newborn rat central nervous system was studied and compared with the distribution of the glutamate oxaloacetate transaminase activity. The subcellular localization of both enzyme activities was also investigated. These experiments suggest that both enzymes, sometimes considered as identical, are different.     

Glycerol accumulation and water content in larvae of Limenitis archippus: Their importance to winter survival

Half-grown (third instar) larvae of the viceroy butterfly enter facultative winter diapause in response to short-day photoperiod after constructing tubular silk hibernacula in the basal portions of partly eaten willow leaves. Larval water content soon decreases from 80% to about 55%. No detectable quantities of glycerol occur in diapausing larvae maintained at room temperature. Subjection to cold and freezing temperatures causes high levels of glycerol to accumulate (up to 1.9 M or 7.8 g%) within the larvae. These metabolic changes probably lower the supercooling points of the larval fluids and retard both nucleative and inoculative freezing. Diapause termination is not photoperiod dependent, but involves an increase in water content and glycerol breakdown. An unidentified enzyme possibly removes the phosphate group from α-glycerophosphate, thus forming glycerol in the diapausing larvae.     

Comparison of membrane organization in mitochondria from yeast and rat liver by nuclear magnetic resonance spectroscopy

Summary Proton magnetic resonance (PMR) and carbon-13 magnetic resonance (CMR) spectra of intact, unsonicated yeast and rat liver motochondria show differences which may be correlated with the composition of the membranes. High resolution PMR and CMR signals in intact yeast mitochondria have been assigned to regions of fluid lipid-lipid interaction on the basis of spectra of extracted lipid and protein, and the temperature dependence of NMR signals from the intact membrane. PMR spectra suggest that about 20% of total yeast phospholipid is in regions where both intramolecular fatty acid chain mobility and lateral diffusion of entire phospholipid molecules are possible. No such regions appear to exist in rat liver mitochondria. For both yeast and rat liver mitochondria, comparison of PMR and CMR spectra suggests that about 50% of phospholipid appears to be in regions where intramolecular fatty acid chain motion is considerable, but lateral diffusion is restricted. The remaining phospholipid appears to have little inter- or intramolecular mobility. Since NMR observation of lipid extracts from membranes indicates that phospholipid-sterol interactions do not account for the spectra of intact mitochondria, these effects are interpreted in terms of extensive lipid-protein interactions.     

Complementation of human adenovirus type 5 ts mutants by human adenovirus type 12.

Temperature-sensitive mutants of type 5 adenovirus belonging to eight complementation groups were complemented in mixed infection by type 12 adenovirus, whereas mutants of 7 other groups were not enhanced. In some crosses, phenotypic mixing took place. No evidence of recombination between type 5 ts mutants and type 12 was found.     

Bose-Einstein condensation in biological systems

A theoretical model is presented for describing a previously untreated effect of viscosity on the apparent decomposition rate of enzyme-ligand complexes.Since the translational diffusion is hindered by the viscosity, its increased value results in an enlarged portion of ligands which can be rebound by the enzyme immediately after the dissociation of the complex.The model accounts for the experimentally observed decrease in maximal velocity of enzymic reactions at high viscosity. At the same time, it serves as a tool to obtain new information about the energetic processes of enzyme action.     

Recognition of the Trachypetidae stat.n. as a new extant family of Ichneumonoidea (Hymenoptera), based on molecular and morphological evidence

The Trachypetinae (type genus Trachypetus Guérin de Méneville) comprise seven species of large-bodied wasps in three genera (Cercobarcon Tobias, Megalohelcon Turner and Trachypetus) endemic to continental Australia. Historically they have been variously treated, as members of the Helconinae in the case of Megalohelcon, or as separate subfamilies (Cercobarconinae and Trachypetinae). Some 25 years ago they were united in a single subfamily, the Trachypetinae, based on a number of characters. Although there has been conflicting evidence from morphological and molecular phylogenetic studies as to how best to treat the group, there has been a growing consensus that they fall outside the rest of the Braconidae, although taxon sampling has been a limiting factor for molecular studies. We generated a molecular dataset comprising five gene fragments (nuclear 28S ribosomal rDNA, nuclear 18S, elongation factor 1-alpha, mitochondrial 16S rDNA, and mitochondrial cytochrome oxidase subunit 1) for a taxonomically broad range of Braconidae, Ichneumonidae, trachypetines and outgroup hymenopterans including the first molecular data for the trachypetines Cercobarcon and Trachypetus obtained using specially designed internal primers. Molecular and combined molecular and morphological analyses confirm the monophyly of the Trachypetinae and robustly place them as sister to the Braconidae. Detailed morphological analysis including newly recognized characters shows that trachypetines lack several synapomorphies that define the Braconidae, and that they possess a number of symplesiomorphies absent from this family but found in some ichneumonids. We conclude that family-level status is warranted for the group based on both molecular and morphological criteria, and hence we propose the new family, Trachypetidae Schulz stat.n. (type genus Trachypetus Guérin de Méneville), for it. As a result, the remaining extant Braconidae become clearly defined based on synapomorphies not present in Trachypetidae stat.n. This published work has been registered on ZooBank, http://zoobank.org/urn:lsid:urn:lsid:zoobank.org:pub:5418F709-D724-4F14-89D8-1E054D1D27D0 .     

Anticoagulation for the Acute Management of Ischemic Stroke

Few prospective studies support the use of anticoagulation during the acute phase of ischemic stroke, though observational data suggest a role in certain populations. Depending on the mechanism of stroke, systemic anticoagulation may prevent recurrent cerebral infarction, but concomitantly carries a risk of hemorrhagic transformation. In this article, we describe a case where anticoagulation shows promise for ischemic stroke and review the evidence that has discredited its use in some circumstances while showing its potential in others.