Xaa-Arg-Gly triplets in the collagen triple helix are dominant binding sites for the molecular chaperone HSP47.

HSP47 is an essential procollagen-specific molecular chaperone that resides in the endoplasmic reticulum of procollagen-producing cells. Recent advances have revealed that HSP47 recognizes the (Pro-Pro-Gly)(n) sequence but not (Pro-Hyp-Gly)(n) and that HSP47 recognizes the triple-helical conformation. In this study, to better understand the substrate recognition by HSP47, we synthesized various collagen model peptides and examined their interaction with HSP47 in vitro. We found that the Pro-Arg-Gly triplet forms an HSP47-binding site. The HSP47 binding was observed only when Arg residues were incorporated in the Yaa positions of the Xaa-Yaa-Gly triplets. Amino acids in the Xaa position did not largely affect the interaction. The recognition of the Arg residue by HSP47 was specific to its side-chain structure because replacement of the Arg residue by other basic amino acids decreased the affinity to HSP47. The significance of Arg residues in HSP47 binding was further confirmed by using residue-specific chemical modification of types I and III collagen. Our results demonstrate that Xaa-Arg-Gly sequences in the triple-helical procollagen molecule are dominant binding sites for HSP47 and enable us to predict HSP47-binding sites in homotrimeric procollagen molecules.     

Regional differences in the morphology of a shrub Damnacanthus indicus: An induced resistance to deer herbivory?

We report here the possibility of an induced resistance of a spiny shrub Damnacanthus indicus against deer herbivory. Six characters of D. indicus were compared between regions with and without deer herbivory on the Boso Peninsula. We found that D. indicus in browsed areas produced smaller leaves, thicker spines, and shorter internode distances between spines than those in unbrowsed areas whereas the length of spines and the angle of a pair of spines did not differ significantly. It is likely that D. indicus shows an induced resistance by producing smaller leaves, and by increasing stoutness of spines and spine density.     

Rediscovery of Nebela ansata (Amoebozoa: Arcellinida) in eastern North America: biogeographical implications

Aim The question whether free‐living protists are generally cosmopolitan is currently a matter of debate. In this study we investigate the geographical distribution of a distinctive testate amoeba species, Nebela ansata, and use our data to assess the potential for highly restricted distribution patterns in some protist species. Location Global. Methods We analysed (1) 3400 testate amoeba publications from North America and other continents, (2) unpublished slides of the Penard Collection of the Natural History Museum, London, UK, and (3) 104 Sphagnum samples from eastern North America. Non‐metric multidimensional scaling (NMDS) was used to visualize the similarities in testate amoeba community composition among 1012 North American samples, including two communities that contained N. ansata. Results We rediscovered N. ansata at a site in New Jersey located close to its type locality, and in Nova Scotia. We also report the existence of an apparently unpublished museum specimen originally collected from New Jersey. Our extensive literature survey confirmed the presence of this species only in the temperate part of eastern North America. The NMDS revealed that communities with N. ansata were less similar to each other than to communities from other parts of North America, suggesting that favourable habitats for N. ansata occur in other Sphagnum‐dominated peatlands, a habitat type that has been extensively sampled in North America and elsewhere. Main conclusions These data provide an unusually convincing case of a free‐living microorganism with a very limited distribution range in the temperate part of eastern North America. The remarkably restricted distribution of N. ansata highlights the extent of our ignorance about the natural history of free‐living microorganisms, and raises questions about the lack of attention to microbial diversity in conservation biology.     

Excitability Changes of the Mauthner Cell during Collateral Inhibition

Excitability changes during collateral inhibition of the goldfish Mauthner cell (M cell) were measured directly by stimulating the cell with current pulses applied through an intracellular electrode. Excitability was suppressed during the extrinsic hyperpolarizing potential (EHP) as well as during the collateral IPSP. The inhibitory effect of the EHP was shown to be comparable in intensity to the effect of the IPSP. Excitability changes in the M cell during collateral IPSP depended on changes in the membrane conductance as well as in the membrane potential. Some simple equations are advanced which describe the excitability change during the IPSP in terms of changes in membrane potential and conductance. It was also found that invasion of antidromic impulses into the M cell was suppressed during the EHP, but not during the collateral IPSP. Conductance increase during the IPSP did not interfere with the invasion of antidromic impulses.     

Human T-cell hybridomas producing migration inhibitory factor and macrophage activating factors

Studies were carried out to determine the heterogeneity of factors that affect macrophage functions using human hybridomas constructed by fusing PHA-activated human peripheral blood lymphocytes with emetine-actinomycin D-pretreated cloned human acute lymphatic leukemia cells (CEM). Three assay systems were used to investigate the activity of the macrophage migration inhibitory factor and of the macrophage activation factors for glucose consumption (MAF-G) and for O2- formation. In the culture supernatant of hybridomas and other cells, various combinations of these activities were detected. The results indicate that at least three molecules are concerned in each of these activities.     

Increased Levels of Monodehydroascorbate Radical in UV-B-Irradiated Broad Bean Leaves

Light-induced monodehydroascorbate (MDA) radical productionwas not detectable by EPR spectroscopy in untreated broad beanleaves, but it was observed after exposing the leaves to UV-B(280–320 nm) irradiation. After this pre-treatment, alow level of MDA radicals was also detectable without illumination.Light-induced MDA, MDA production in the dark, oxygen evolution,quantum yield of PSII as measured by Chi fluorescence, MDA producingand reducing enzyme activities were determined and comparedin leaves after irradiation with various doses of UV-B. Ourresults suggest that UV-B irradiation disturbs the balance ofMDA radical production and reduction, resulting in increasedlight induced MDA signal. The enhancement of ascorbate photooxidationat the UV-B damaged donor side of PSII appears as a major factorin this process. (Received November 22, 1996; Accepted March 25, 1997)     

Ascorbate in thylakoid lumen as an endogenous electron donor to Photosystem II: Protection of thylakoids from photoinhibition and regeneration of ascorbate in stroma by dehydroascorbate reductase

Photoinhibition of the electron transport activity from tyrosine Z (Y_Z) in PS II to NADP⁺in Tris-treated thylakoids was suppressed by electron donation with either diphenylcarbazide or ascorbate (AsA) during the photoinhibition treatment. This suggests that AsA prevents donor side-induced photoinhibition in vivo as an endogenous donor. AsA in the lumen is photooxidized to monodehydroascorbate (MDA) in Tris-treated thylakoids, as detected by electron spin resonance spectrometry, but not in oxygenic thylakoids. Redox analysis of pyridine nucleotide in the presence of either MDA reductase or dehydroascorbate (DHA) reductase showed that the MDA photoproduced in the lumen is disproportionated to AsA and DHA, and the DHA leaking into the stroma is reduced to AsA by DHA reductase. No leakage of MDA through the thylakoid membrane was observed. Thus, the DHA-reducing enzyme system is indispensable in maintaining AsA concentrations in chloroplasts.     

Gender differences in effects of 20 days horizontal bed rest on muscle strength in young subjects

Gender differences in the effect of 20 days bed rest (BR) on muscle strength were evaluated in voluntary 11 male and 7 female students. Maximum Isometric Voluntary Contractions (MVC) of 4 right arm muscles (RAM), 5 right leg muscles (RLM), and 2 body trunk muscles were measured with an isometric dynamometer, respectively. Muscle masses (MM) of right arm and leg and body trunk were determined by dual energy X-ray absorptiometry, respectively. The maximum cross sectional area (CSAmax) of right m. quadriceps femoris was measured by magnetic resonance imaging. Elbow flexion MVC in males and all MVC of RLM except knee flexion in both males and females were decreased (p<0.05), but elbow extension MVC in females was increased (p<0.05), while all of other MVC only tended to decrease. However, the decrements in leg MVC were not correlated to the leg MM, and also the decrement in knee extension was not correlated to the CSAmax of m. quadriceps. The reduction of MVC of antigravity muscles might be caused not only by a decrease in MM but also by other factors. The greater decrements of leg MVC during BR were the higher initial level in males, but the inverse was observed in females. However, this discrepancy between males and females cannot be explained in the present study.     

Effects of 20 days horizontal bed rest on kinesthesia during knee flexion and two-point discrimination in skin of young subjects

Investigating the effect of 20 days bed rest (BR) on kinesthesia and two-point discrimination, 10 young volunteers participated in this study as subjects. Angle position sensation of right knee was measured in the prone position during flexion and extension monitored by a goniometer after two-point discrimination in skin was determined on the same lower leg. Flexed constant error was unchanged but directional constant error and absolute error were increased after BR (p<0.05). Two-point discrimination was unchanged after BR, which brought about a decline of the orientation of moving the joint indicated as over shooting of the angle during knee flexion, while it did not affect superficial sensation observed by two-point discrimination. Probably, an adjustment of deep sensation to the knee joint is lowered by the reduction in kinesthesia as well as the sensory disturbance during BR, which is independent on information from superficial sensation.     

Landscape structure affects food quality of sika deer (<Emphasis Type="Italic">Cervus nippon</Emphasis>) evidenced by fecal nitrogen levels

Evaluating the quality of wildlife habitat is essential for understanding and predicting population dynamics in heterogeneous environments. We used fecal nitrogen levels as an indicator of habitat quality of sika deer (Cervus nippon) and explored important landscape elements influencing nitrogen levels, taking deer density into account. We established 92 plots differing in deer density and landscape structure on the Boso Peninsula, central Japan, and collected fecal samples along a 1-km transect at each plot. The regression models involving two independent variables, i.e., deer density and the length of forest edge within an area of 100 or 200 m from the transect, were selected based on the Akaike’s Information Criterion (AIC). Levels of fecal nitrogen were positively correlated with the length of the forest edge and negatively correlated with population density of deer. The area of 100 or 200 m from the transect most likely reflected the behavioral scale of the deer. Coverage of palatable understory vegetation increased with proximity to forest edge and decreased with deer density. Variability in the level of fecal nitrogen could thus be explained by food availability in the landscape. These results suggest that landscape alterations increase the carrying capacity of sika deer and thereby increase impacts upon the ecosystem.