Comparative structure of vesicular-arbuscular mycorrhizas and ectomycorrhizas

During the establishment of vesicular-arbuscular mycorrhizas, fungal hyphae contact the root surface, form appressoria and initiate the internal colonization phase. Structural changes occur in the cell wall, the cytoplasm and the nucleus as the fungus progresses from a presymbiotic to a symbiotic phase. Nuclei in spores are in G₁ whereas in intraradical hyphae they are in G₁ and G₂. Changes in nuclear organization are evident in various stages in the colonization process. Dramatic changes in both symbionts occur as the nutrient exchange interface is established between arbuscules and root cortical cells. An interfacial matrix, consisting of molecules common to the primary wall of the cortical cell, separates the cortical cell plasma membrane from the fungal cell wall. Ectomycorrhizas are characterized structurally by the presence of a mantle of fungal hyphae enclosing the root and usually an Hartig net of intercellular hyphae characterized by labyrinthine branching. As hyphae contact the root surface, they may respond by increasing their diameter and switching from apical growth to precocious branching. The site of initial contact of hyphae may be either the root cap or the ‘mycorrhiza infection zone’. The mantle varies considerably in structure depending on both the plant and fungus genome. In some ectomycorrhizas, the mantle may be a barrier to apoplastic transport, and in most it may store polyphosphate, glycogen, lipids and perhaps protein.     

The pharmacophore of the human C5a anaphylatoxin.

We have determined which amino acids contribute to the pharmacophore of human C5a, a potent inflammatory mediator. A systematic mutational analysis of this 74-amino acid protein was performed and the effects on the potency of receptor binding and of C5a-induced intracellular calcium ion mobilization were measured. This analysis included the construction of hybrids between C5a and the homologous but unreactive C3a protein and site-directed mutagenesis. Ten noncontiguous amino acids from the structurally well-defined 4-helix core domain (amino acids 1-63) and the C-terminal arginine-containing tripeptide were found to contribute to the pharmacophore of human C5a. The 10 mostly charged amino acids from the core domain generally made small incremental contributions toward binding affinity, some of which were independent. Substitutions of the C-terminal amino acid Arg 74 produced the largest single effect. We also found the connection between these 2 important regions to be unconstrained.     

Detection of gaps in sinusoids by frog auditory nerve fibers: importance in AM coding

Physiological studies were carried out in the frog (Rana pipiens pipiens) eighth nerve to determine: (i) whether the modulation rate or the silent gap was the salient feature that set the upper limit of time-locking to pulsed amplitude-modulated (PAM) stimuli, (ii) the gap detection capacity of individual eighth nerve fibers. Time-locked responses of 79 eighth nerve fibers to PAM stimuli (at the fiber's characteristic frequency) showed that the synchronization coefficient was a low-pass function of the modulation rate. In response to PAM stimuli having different pulse durations, a fiber gave rise to non-overlapping modulation transfer functions. The upper cut-off frequency of time locking was higher when tonepulses in PAM stimuli had shorter duration. The fact that the cut-off frequency was different for the different PAM series suggested that the AM rate was neither the sole, nor the main, determinant for the decay in time-locking at high AM rates. Gap detection capacity was determined for 69 eighth nerve fibers by assessing fiber's spiking activities to paired tone-pulses during an OFF-window and an ON-window. It was found that the minimum detectable gap of eighth nerve fibers ranged from 0.5 to 10 ms with an average of 1.23–2.16 ms depending on the duration of paired tone pulses. For each fiber, the minimum detectable gap was longer when the duration of tone pulses comprising the twin-pulse stimuli was more than four times longer. When the synchronization coefficient was plotted against the silent gap between tones pulses in the PAM stimuli, the gap response functions of a fiber as derived from multiple PAM series were equivalent to gap response functions deriving from twin-pulse series suggesting that it was the silent gap which primarily determined the upper limit of time-locking to PAM stimuli.Abbreviations MTF modulation transfer function - PAM pulse amplitude modulated - SAM sinusoidally amplitude modulated - SC synchronization coefficient - TW time window     

Distribution of zinc metallothionein I mRNA in rat brain using in situ hybridization

Metallothionein (MT) isoforms I and II were first identified and characterized in our laboratories in several regions of brain, in hippocampal neurons in primary culture, and in retinoblastoma and neuroblastoma cell lines. In this study, by having employed the MT-I cDNA as a probe, we sought to gain additional insight about the function of MT by discerning the regional distribution of its mRNA. Northern blot analyses of brain mRNA revealed that the administration of zinc enhanced dramatically MT-I mRNA (570 bp). The in situ hybridization study revealed that MT-I mRNA was located in several areas of brain, with the highest concentrations found in the cerebellum, hippocampus, and ventricles. The results of these studies are interpreted to suggest that zinc enhances the synthesis of MT mRNA and MT in turn may participate in zinc associated functions in neurons.Abbreviations MT-I Metallothionein I isoform - mRNA Messenger ribonucleic acid - ³⁵S dCTP ³⁵S Deoxycytidine triphosphate - ³²P dCTP ³²P Deoxycytidine triphosphate - icv Intracerebroventricularly - IP Intraperitoneally - PBS Paraformaldehyde phosphate buffered saline solution - Tris 2 amino-2-hydroxymethylpropane-1,3 diol - EDTA Ethylenediaminetetraacetic acid - cDNA Complimentary deoxyribonucleic acid - bp Base pair     

Collective motions in proteins investigated by X-ray diffuse scattering

We have developed theoretical models for analysis of X-ray diffuse scattering from protein crystals. A series of models are proposed to be used for experimental data with different degrees of precision. First, we propose the normal mode model, where conformational dynamics of a protein is assumed to occur mostly in a limited conformational subspace spanned by a small number of low-frequency normal modes in the protein. When high precision data are available, variances and covariances of the normal mode variables can be determined from experimental data using this model. For experimental data with lower degrees of precision, we introduce a series of simpler models. These models express the covariance matrix using relatively simple empirical correlation functions by assuming the correlation between a pair of atoms to be isotropic. As an application of these simpler models, we calculate diffuse-scattering patterns from a human lysozyme crystal to examine how each adjustable parameter in the models affects general features of the resulting patterns. The results of the calculation are summarized as follows. (1) The higher order scattering makes a significant contribution at high resolutions. (2) The resulting simulated patterns are sensitive to changes in correlation lengths of about 1 Å, as well as to changes of the functional form of the correlation function. (3) But only the “average” value of the intra- and intermolecular correlation lengths seems to determine the gross features of the pattern. (4) The effect of the atom-dependent amplitude of fluctuations is difficult to observe. © 1994 John Wiley & Sons, Inc.     

触珠蛋白研究进展

触珠蛋白是一种酸性糖蛋白,属急性期反应蛋白之一,由于所含轻链类型的不同,触珠蛋白具有遗传多态性,触珠蛋白的合成和降解主要在肝脏进行,并受细胞因子、前列腺素、激素等的调节,触珠蛋白具有广泛的生物学功能,可能是一种重要的调节蛋白.     

Differential responses to copper in rainbow trout (Oncorhynchus mykiss) acclimated to sea water and brackish water

Rainbow trout, Oncorhynchus mykiss, acclimated to 33% sea water (12 mg·ml^-1 salinity) experienced significant (10 meq·1^-1) increases in plasma [Na⁺] and [Cl^-] within 5 h of exposure to 6.3 mol copper·1^-1 indicating severe impairment of branchial ionoregulatory capacity. All plasma ion levels subsequently stabilised once the transbranchial [Na⁺] gradient was reduced to zero. The similar ionic strength of the external medium and their body fluids appeared to protect trout maintained in 33% sea water from further ionoregulatory stress and any secondary physiological disturbances during exposure to copper. Despite three- and fourfold greater transbranchial [Na⁺] and [Cl^-] gradients, trout acclimated to full-strength sea water (35 mg·ml^-1 salinity) suffered no major changes in plasma Na⁺, Cl^-, K⁺, or Ca²⁺, blood gases or haematology during 24 h exposure to 6.3 mol copper·1^-1. This reduction in toxicity in full strength sea water cannot be explained by differences in copper speciation. We suggest that during acute exposure to waterborne copper, active NaCl extrusion is unaffected due to the basolateral location of the gill Na⁺/K⁺-ATPase, but that ionoregulatory disturbances can occur due to gill permeability changes secondary to the displacement of surface-bound Ca²⁺. However, in full strength sea water the three-fold higher ambient [Ca²⁺] and [Mg²⁺] appear to be sufficient to prevent any detrimental permeability changes in the presence of 6.3 mol copper·1^-1. Plasma [NH ₊ ⁴ ] and [HCO _- ³ ] were both significantly elevated during exposure to copper, indicating that some aspects of gill ion transport (specifically the apical Na⁺/NH ₊ ⁴ and Cl^-/HCO _- ³ exchanges involved in acid/base regulation and nitrogenous waste excretion) are vulnerable to inhibition in the presence of waterborne copper.Abbreviations C _aO₂ arterial oxygen content - Hb haemoglobin - Hct haematocrit - MABP mean arterial blood pressure - MCHC mean cell haemoglobin content - MO₂ rate of oxygen consumption - P _a CO₂ arterial carbon dioxide tension - P _aO₂ arterial oxygen partial pressure - S salinity - SW sea water - T _Amm total ammonia (=NH₃+NH ₊ ⁴ ) - T _{CO 2} total carbon dioxide - TEP transepithelial potential - TOC total organic carbon - %Hb-O₂ percentage of haemoglobin saturated with oxygen     

Membrane function and vascular reactivity

This communication examines the possibility that nitric oxide (NO) production by endothelial cells results from changes in cell membrane fluidity. Lysophosphatidylcholine (LPC) alters fluidity of the endothelial cell membranes causing vascular relaxation. Through membrane alterations LPC influences function of a number of membrane receptors and modulates enzyme activity. As a result of detergent action, lysophosphatidylcholine (LPC) causes activation of guanylate cyclase, stimulates syalytransferase and regulates protein kinase C activity. It has already been demonstrated that ionic detergents, such as Triton X-100 also cause vascular relaxation, possibly induced by NO production from endothelial cells. It is postulated that production of nitric oxide results from changes in membrane viscosity; this may represent a mechanism for its regulation in biological systems.     

Submaximal,aerobic exercise training exacerbates the cardiomyopathy of postweanling Cu-depleted rats

To determine the dual effect of exercise training and copper depletion on myocardial function and ultrastructure, postweanling rats were either trained or sedentary while fed copper-adequate or copper-deficient diets for 8 wk. Rats developed characteristic myocardial subcellular degeneration and increased cardiac mitochondrial volume density when copper depleted, despite lack of overt cardiac hypertrophy, hypertension, or anemia. Training combined with copper depletion induced mild left ventricular hypertrophy. Basal laminae appeared fractionated in areas at capillary-myocyte interface, with focal pericapillary and interstitial collagen accumulation, where-as overt fibrosis was absent or minimal. Electrocardiograms revealed increased QRS wave and QT duration and notching of QRS complex with copper depletion, consistent with intraventricular conductance disturbances. The oxidative capacity of soleus muscle increased with training in copper-adequate rats, but was reduced with progressive copper depletion. These data suggest that copper depletion and training are synergistic in effecting focal accumulation of collagen, with deleterious effect on exercise capacity.     

Human TRP-1 Has Tyrosine Hydroxylase but no DOPA Oxidase Activity

Human TRP-1 has been immunopurified from normal human melanocytes cultured from black neonatal subjects and used to investigate the catalytic function of TRP-1 for the two substrates, L-tyrosine and L-DOPA. Immunopurified TRP-1 did not demonstrate DOPA staining on SDS/PAGE nor DOPA oxidase (DO) activity with either routine or modified assays. The purified TRP-1 also demonstrated no tyrosine hydroxylase (TH) activity using the routine Pomerantz assay. However, there was apparent TH activity exhibited by immunopurified TRP-1 under conditions with low tyrosine concentration (≤0.8 μCi/ml of ³H-tyrosine), prolonged incubation time (i.e., overnight) and in the absence of the cofactor L-DOPA. Using these latter specific conditions, TH activity was also detected in cell lysates from a tyrosinase-negative albino melanocyte line which exhibited no TH activity with the routine Pomerantz assay. In addition, TH activity under low substrate assay conditions was not exhibited in a melanocyte line derived from a TRP-1 deficient, Brown albino individual. However, the absence of TH in this Brown albino cell line could be compensated for by the addition of L-DOPA to the assay. These results suggested that TRP-1 has some tyrosine hydroxylase but no DOPA oxidase activity. We propose that one function of TRP-1 is to modulate tyrosinase activity by making DOPA available as a cofactor to perpetuate the initial steps in melanogenesis.