The ability of rufous hummingbirds Selasphorus rufus to dilute and concentrate urine

Most terrestrial animals face the challenge of having to conserve water in a desiccating environment. Not surprisingly, the ability to produce concentrated urine has been relatively well studied in birds. Nectar-feeding birds are unusual among terrestrial animals in that they often ingest and excrete prodigious water volumes to obtain adequate energy. Thus, they confront the unusual challenge of having to conserve electrolytes. The diluting abilities of birds and the renal mechanisms that may correlate with them have been relatively neglected. To elucidate diluting and concentrating abilities in nectar-feeding birds, we fed rufous hummingbirds Selasphorus rufus an electrolyte-free nectar and a nectar containing a range of NaCl concentrations. Hummingbirds had a spectacular (and possibly unique) diluting ability: when fed on electrolyte-free food they produced excreta containing less than 0.5 mM l⁻¹ each of sodium and potassium. Hummingbirds also had a poor concentrating ability, retaining sodium and chloride when their food (0.632 M l⁻¹ sucrose) contained more than 35 mM l⁻¹ of NaCl. The kidneys of hummingbirds do not appear to be suited for concentrating urine, and possibly contain structural features that give them a unique diluting ability compared with those of birds that do not feed on nectar.     

The solvent in CNBr cleavage reactions determines the fragmentation efficiency of ketosteroid isomerase fusion proteins used in the production of recombinant peptides

Abnormal fragmentation during cyanogen bromide polypeptide cleavage rarely occurs, although parallel side reactions are known to typically accompany normal cleavage. We have observed that cyanogen bromide cleavage of highly hydrophobic fusion proteins utilized for production of recombinant peptides results in almost complete abolishment of the expected reaction products when the reaction is carried out in 70% trifluoroacetic acid. On the basis of mass spectrometric analysis of the reaction products, we have identified a number of fragments whose origin can be attributed to incomplete fragmentation of the fusion protein, and to unspecific degradation affecting the carrier protein. Substituting the solvent in the reaction media with 70% formic acid or with a matrix composed of 6M guanidinium hydrochloride in 0.1M HCl, however, was found to alleviate polypeptide cleavage. We have attributed the poor yields of the CNBr cleavage carried out in 70% TFA to the increased hydrophobicity of our particular fusion proteins, and to the poor solubilizing ability of this reaction medium. We propose the utilization of chaotropic agents in the presence of diluted acids as the preferred cyanogen bromide cleavage medium of fusion proteins in order to maximize cleavage efficiency of hydrophobic sequences and to prevent deleterious degradation and structural modifications of the target peptides.     

Effect of viscoelastic relaxation on moisture transport in foods. Part I: Solution of general transport equation

Within the framework of continuum mechanics, Singh et al. [1] developed an integro-differential equation, which applies to both Darcian (Fickian) and non-Darcian (non-Fickian) modes of fluid transport in swelling biological systems. A dimensionless form of the equation was obtained and transformed from moving Eulerian to the stationary Lagrangian coordinates. Here a solution scheme for the transport equation is developed to predict moisture transport and viscoelastic stresses in spheroidal biopolymeric materials. The equation was solved numerically and results used for predicting drying and sorption curves, moisture profiles, and viscoelastic stresses in soybeans. The Lagrangian solution was obtained by assembling together several schemes: the finite element method was used to discretize the equation in space; non-linearity was addressed using the Newton-Raphson method; the Volterra term was handled via a time integration scheme of Patlashenko et al. [2] and the Galerkin rule was used to solve the time-differential term. The solution obtained in Lagrangian coordinates was transformed back to the Eulerian coordinates. In part II of this sequence we present the numerical results.Revised version: 5 October 2003     

A hybrid model for erythrocyte membrane: a single unit of protein network coupled with lipid bilayer

To investigate the nanomechanics of the erythrocyte membrane we developed a hybrid model that couples the actin-spectrin network to the lipid bilayer. This model features a Fourier space Brownian dynamics model of the bilayer, a Brownian dynamics model of the actin protofilament, and a modified wormlike-chain model of the spectrin (including a cable-dynamics model to predict the oscillation in tension). This model enables us to predict the nanomechanics of single or multiple units of the protein network, the lipid bilayer, and the effect of their interactions. The present work is focused on the attitude of the actin protofilament at the equilibrium states coupled with the elevations of the lipid bilayer through their primary linkage at the suspension complex in deformations. Two different actin-spectrin junctions are considered at the junctional complex. With a point-attachment junction, large pitch angles and bifurcation of yaw angles are predicted. Thermal fluctuations at bifurcation may lead to mode-switching, which may affect the network and the physiological performance of the membrane. In contrast, with a wrap-around junction, pitch angles remain small, and the occurrence of bifurcation is greatly reduced. These simulations suggest the importance of three-dimensional molecular junctions and the lipid bilayer/protein network coupling on cell membrane mechanics.     

Short term hypothyroidism affects ovarian function in the cycling rat

Background  

Rats made hypothyroid with propilthyouracil start showing abnormal cycling on the second cycle after the start of the treatment, with a high proportion of spontaneous pseudopregnancies and reduced fertility.     

Small-scale elevational variation in the abundance of Eufriesea violacea (Blanchard) (Hymenoptera: Apidae)

Eufriesea violacea (Blanchard) males were sampled in a small-scale elevational gradient in Southeastern Brazil and showed sequential peaks of abundance from lowest (700 m) to highest (1,100 m) altitudes during the sampling period. The influence of the temperature on the length of the egg-to-adult period and flowering dates of plants producing food (nectar) suggests that it may be one of the factors determining the distribution of male abundance along the altitudinal gradient. The results emphasize the importance of obtaining altitudinal stratified samples when studying Euglossini populations, especially when the studies are done at sites with marked topographical variation.     

Enzymatic processing of angiotensin peptides by human glomerular endothelial cells

The intraglomerular renin-angiotensin system (RAS) is linked to the pathogenesis of progressive glomerular diseases. Glomerular podocytes and mesangial cells play distinct roles in the metabolism of angiotensin (ANG) peptides. However, our understanding of the RAS enzymatic capacity of glomerular endothelial cells (GEnCs) remains incomplete. We explored the mechanisms of endogenous cleavage of ANG substrates in cultured human GEnCs (hGEnCs) using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and isotope-labeled peptide quantification. Overall, hGEnCs metabolized ANG II at a significantly slower rate compared with podocytes, whereas the ANG I processing rate was comparable between glomerular cell types. ANG II was the most abundant fragment of ANG I, with lesser amount of ANG-(1-7) detected. Formation of ANG II from ANG I was largely abolished by an ANG-converting enzyme (ACE) inhibitor, whereas ANG-(1-7) formation was decreased by a prolylendopeptidase (PEP) inhibitor, but not by a neprilysin inhibitor. Cleavage of ANG II resulted in partial conversion to ANG-(1-7), a process that was attenuated by an ACE2 inhibitor, as well as by an inhibitor of PEP and prolylcarboxypeptidase. Further fragmentation of ANG-(1-7) to ANG-(1-5) was mediated by ACE. In addition, evidence of aminopeptidase N activity (APN) was demonstrated by detecting amelioration of conversion of ANG III to ANG IV by an APN inhibitor. While we failed to find expression or activity of aminopeptidase A, a modest activity attributable to aspartyl aminopeptidase was detected. Messenger RNA and gene expression of the implicated enzymes were confirmed. These results indicate that hGEnCs possess prominent ACE activity, but modest ANG II-metabolizing activity compared with that of podocytes. PEP, ACE2, prolylcarboxypeptidase, APN, and aspartyl aminopeptidase are also enzymes contained in hGEnCs that participate in membrane-bound ANG peptide cleavage. Injury to specific cell types within the glomeruli may alter the intrarenal RAS balance.     

Prediction of survival by neutropenia according to delivery schedule of oxaliplatin-5-Fluorouracil-leucovorin for metastatic colorectal cancer in a randomized international trial (EORTC 05963)

Circadian clocks control cellular proliferation and drug metabolism over the 24?h. However, circadian chronomodulated chemotherapy with 5-fluorouracil, leucovorin, and oxaliplatin (chronoFLO4) offered no survival benefit as compared with the non-time-stipulated FOLFOX2, in an international randomized trial involving patients with previously untreated metastatic colorectal cancer (EORTC 05963). The authors hypothesized that treatment near maximum tolerated dose could disrupt circadian clocks thus impairing the efficacy of chronoFLO4 but not of FOLFOX2. Patients with available data (N?=?556) were categorized into three subgroups according to the worst grade (G) of neutropenia experienced during treatment. Distinct multivariate models with time-dependent covariates were constructed for each treatment schedule. Neutropenia incidence (all grades) was 33% on chronoFLO4 and 61% on FOLFOX2 (p?相似文献   

Palmitoylation-induced Aggregation of Cysteine-string Protein Mutants That Cause Neuronal Ceroid Lipofuscinosis

Recently, mutations in the DNAJC5 gene encoding cysteine-string protein α (CSPα) were identified to cause the neurodegenerative disorder adult-onset neuronal ceroid lipofuscinosis. The disease-causing mutations (L115R or ΔL116) occur within the cysteine-string domain, a region of the protein that is post-translationally modified by extensive palmitoylation. Here we demonstrate that L115R and ΔL116 mutant proteins are mistargeted in neuroendocrine cells and form SDS-resistant aggregates, concordant with the properties of other mutant proteins linked to neurodegenerative disorders. The mutant aggregates are membrane-associated and incorporate palmitate. Indeed, co-expression of palmitoyltransferase enzymes promoted the aggregation of the CSPα mutants, and chemical depalmitoylation solubilized the aggregates, demonstrating that aggregation is induced and maintained by palmitoylation. In agreement with these observations, SDS-resistant CSPα aggregates were present in brain samples from patients carrying the L115R mutation and were depleted by chemical depalmitoylation. In summary, this study identifies a novel interplay between genetic mutations and palmitoylation in driving aggregation of CSPα mutant proteins. We propose that this palmitoylation-induced aggregation of mutant CSPα proteins may underlie the development of adult-onset neuronal ceroid lipofuscinosis in affected families.