Comparative energy measurements in single molecule interactions

Single molecule experiments have opened promising new avenues of investigations in biology, but the quantitative interpretation of results remains challenging. In particular, there is a need for a comparison of such experiments with theoretical methods. We experimentally determine the activation free energy for single molecule interactions between two synaptic proteins syntaxin 1A and synaptobrevin 2, using an atomic force microscope and the Jarzynski equality of nonequilibrium thermodynamics. The value obtained is shown to be reasonably consistent with that from single molecule reaction rate theory. The temperature dependence of the spontaneous dissociation lifetime along with different pulling speeds is used to confirm the approach to the adiabatic limit. This comparison of the Jarzynski equality for intermolecular interactions extends the procedure for calculation of activation energies in nonequilibrium processes.     

A ligand field chemistry of oxygen generation by the oxygen-evolving complex and synthetic active sites

Oxygen-oxygen bond formation and O2 generation occur from the S4 state of the oxygen-evolving complex (OEC). Several mechanistic possibilities have been proposed for water oxidation, depending on the formal oxidation state of the Mn atoms. All fall under two general classifications: the AB mechanism in which nucleophilic oxygen (base, B) attacks electrophilic oxygen (acid, A) of the Mn4Ca cluster or the RC mechanism in which radical-like oxygen species couple within OEC. The critical intermediate in either mechanism involves a metal oxo, though the nature of this oxo for AB and RC mechanisms is disparate. In the case of the AB mechanism, assembly of an even-electron count, high-valent metal-oxo proximate to a hydroxide is needed whereas, in an RC mechanism, two odd-electron count, high-valent metal oxos are required. Thus the two mechanisms give rise to very different design criteria for functional models of the OEC active site. This discussion presents the electron counts and ligand geometries that support metal oxos for AB and RC O-O bond-forming reactions. The construction of architectures that bring two oxygen functionalities together under the purview of the AB and RC scenarios are described.     

Hyperleptinemia--non-haemodynamic risk factor for the left ventricular hypertrophy development in hypertensive overweight females

Obesity is directly and strongly associated with hypertension and left ventricular hypertrophy (LVH). Development of LVH is multifactorial, caused both by haemodynamic and non-haemodynamic factors. Hypertension is the main haemodynamic factor. Humoral mechanisms, as a non-haemodynamic factor for LVH development, have not been completely explained. The aim of this study is to determine whether hyperleptinemia can be one of humoral--non-haemodynamic factor inducing LVH together with haemodynamic factors in overweight females. The study was done on thirty six adult, overweight female patients, body mass index in range 25-30 kg/m2. Patients are nondiabetic with regular renal function. Twenty one female patients were hypertensive with left ventricular hypertrophy. Control group included fifteen hypertensive female patients without left ventricular hypertrophy. In all patients was determined glucose profile and creatinine clearance, cholesterol, triglycerides, LDL, HDL. Weight, high, circumference of the waist and hips was taken. Cardiovascular determination was done applying two-dimensional ultrasound. Serum leptin level was measured using radioimmunoassay method (RIA). Results showed that serum leptin level was significantly higher in hypertensive, overweight females with LVH. This suggests that non-haemodynamic factors, such as hyperleptinemia, participate in left ventricular hypertrophy development together with haemodynamic factors in adult hypertonic, overweight females.     

Why be a honeyless honey mesquite? Reproduction and mating system of nectarful and nectarless individuals

Populations of Prosopis glandulosa var. torreyana in the Chihuahuan desert have a fixed dimorphic system of nectar production in which half the individuals produce nectar (are nectarful) and the other half are nectarless. We analyzed the impact of nectar production on different estimates of fitness, comparing nectarful against nectarless individuals in size, mating system, seed traits, and fruit set in a 1-ha scrubland. Of the reproductive individuals (358), 46% were nectarful and 54% were nectarless. Neither tree size nor flowering phenology differed between nectar morphs. Fixation indices (F) for both progeny (F = −0.2) and adults (F = −0.45) were negative, and high heterozygosities were found in adults and progeny (H = 0.45). No differences were found between nectar morphs for F, H, and single (t_s = 1.1) and multilocus (t_m = 1.03) outcrossing rates. Controlled pollinations showed differences between selfing and control treatments with no differences between nectar morphs. Nectarless individuals produced significantly more pollen grains than did nectar producers, but all other measured floral traits showed no differences. Nectarful trees were visited by pollinators 21 times more often and had a significantly higher overall fruit set than did nectarless trees. No differences between nectar morphs in seed mass or in percentage seed germination were found, but heavier seeds tended to have higher heterozygosities. Both morphs had similar success as females, but nectarless trees had ∼7% higher male function. We discuss three possible scenarios for the evolution of the fixed dimorphism in nectar production, two involving unstable phases (substitution of one morph by the other, and evolution towards dioecy) and one stable scenario (maintenance of the dimorphic system).     

Hepatic and pancreatic glycosphingolipid phenotypes of the neurological different rat strains

Among three commonly used strains of laboratory rats, Wistar rats perform more neurological tasks better then Lewis and Sprague-Dawley (SD) rats. Liver is the main site of insulin-like growth factor (IGF) production and pancreas is the exclusive site of insulin production. Insulin stimulates neuronal development and appropriate IGF-I input is critical in brain growth. Glycosphingolipids (GSLs) are important mediators of insulin secretion and action. Therefore, this study investigated GSL phenotypes of liver and pancreas with hypothesis that they are different in three rat strains. Total GSL fractions (neutral and gangliosides) were analysed by high performance thin-layer chromatography (HPTLC). Complex gangliosides were detected by HPTLC immunostaining using cholera toxin B subunit after neuraminidase pretreatment. Wistar rats had the highest liver weight/body weight ratio and SD rats had the highest pancreas weight/body weight ratio. Ganglioside GM3 was more expressed in the liver of Wistar compared to Lewis and SD rats. SD rats contained scarce quantities of GD1a and b-series gangliosides in the liver compared to Wistar and Lewis rats. Pancreatic b-series ganglioside content was also the lowest in SD rats. This study represents differences in the hepatic and pancreatic ganglioside phenotypes of three rat strains that could influence IGF and insulin secretion and action.     

Oxygenation alters ganglioside expression in rat liver following partial hepatectomy

Gangliosides from livers of weanling rats were analyzed after 15% partial hepatectomy (PH) and different pre- and post-operative hyberbaric oxygenation (pre- and postHBO). Neu5Ac was the predominant ganglioside-derived sialic acid (>85%) compared to Neu5Gc. Almost identical low total sialic acid content (Neu5Ac+Neu5Gc) of the control and operated nonHBO animals opposed a 6.4- to 7.6-fold increase in pre- and postHBO animals (69.26 and 81.64pmol/mg wet weight, respectively). NanoESI-QTOF mass spectrometry combined with HPTLC immunostaining revealed GM3(Neu5Ac) and GM3(Neu5Gc) as major gangliosides, correlating with the respective sialic acid concentrations. Minor neolacto-series gangliosides were enhanced in preHBO and postHBO, but GM1-core gangliosides only in preHBO rats. GM2 and GalNAc-GM1b were clearly detectable in oxygenated rats compared to traces in the control and nonHBO animals. These results point at a functional role of gangliosides in liver growth regulation and reconstitution after PH combined with pre- and post-operative HBO treatment.     

Characterization of a hypercontraction-induced myopathy in Drosophila caused by mutations in Mhc

The Myosin heavy chain (Mhc) locus encodes the muscle-specific motor mediating contraction in Drosophila. In a screen for temperature-sensitive behavioral mutants, we have identified two dominant Mhc alleles that lead to a hypercontraction-induced myopathy. These mutants are caused by single point mutations in the ATP binding/hydrolysis domain of Mhc and lead to degeneration of the flight muscles. Electrophysiological analysis in the adult giant fiber flight circuit demonstrates temperature-dependent seizure activity that requires neuronal input, as genetic blockage of neuronal activity suppresses the electrophysiological seizure defects. Intracellular recordings at the third instar neuromuscular junction show spontaneous muscle movements in the absence of neuronal stimulation and extracellular Ca2+, suggesting a dysregulation of intracellular calcium homeostasis within the muscle or an alteration of the Ca2+ dependence of contraction. Characterization of these new Mhc alleles suggests that hypercontraction occurs via a mechanism, which is molecularly distinct from mutants identified previously in troponin I and troponin T.