Vasoactive intestinal polypeptide: release into hypophyseal portal blood.

Immunoreactive vasoactive intestinal polypeptide (VIP) was present in portal hypophyseal blood of 24 male rats in concentrations (mean, 995 pg per ml) that were approximately 19 times as high as those in systemic arterial blood (mean, 52 pg per ml). The results demonstrate release of VIP from the hypothalamic-neurohypophyseal complex into the portal circulation, and establish a mechanism for direct influence of the peptide on pituitary function.     

Involvement of histidine residues and sulfhydryl groups in the function of the biotin transport carrier of rabbit intestinal brush-border membrane.

Possible involvement of histidine residues and sulfhydryl groups in the function of the intestinal brush-border membrane (BBM) transporter of biotin was investigated. This was done by examining the effects of pretreatment of BBM vesicle (BBMV) isolated from rabbit intestine with the histidine-specific reagent diethyl pyrocarbonate (DEPC) and the sulfhydryl group-specific reagents p-chloromercuribenzenesulfonic acid (p-CMBS) and 7-chloro-4-nitrobenz-2-oxa-1,3-diazole (NBD-Cl) on carrier-mediated biotin transport. Pretreatment of BBMV with DEPC caused significant inhibition in the initial rate of biotin transport without affecting the substrate uptake at equilibrium. Addition of biotin plus Na+ to vesicle suspensions prior to treatment with DEPC provided significant protection to biotin transport. Treatment of DEPC-pretreated vesicles with the reducing agents dithiothreitol and 2,3-dimercaptopropanol failed to reverse the inhibitory effect of DEPC on biotin transport. The inhibitory effect of DEPC was found to be mediated through a marked decrease in the number of the functional biotin transport carriers with no change in their affinity, as indicated by the severe inhibition in the Vmax but not the apparent Km of the biotin transport process, respectively. Pretreatment of BBMV with p-CMBS and NBD-Cl also caused significant inhibition in the initial rate of biotin transport without affecting the substrate uptake at equilibrium. Addition of biotin plus Na+ to vesicle suspensions prior to treatment with p-CMBS (or NBD-Cl) failed to protect biotin transport from inhibition. On the other hand, treatment of vesicles pretreated with p-CMBS (or NBD-Cl) with the reducing agents dithiothreitol and mercaptoethanol caused significant reversal in the inhibition of biotin transport. The inhibitory effects of p-CMBS (and NBD-Cl) on biotin transport was also found to be mediated through inhibition in the Vmax, but not the apparent Km, of biotin transport process. These results indicate the involvement of histidine residues and sulfhydryl groups in the normal function of the biotin transport system of rabbit intestinal BBM. Furthermore, the results also suggest that the histidine residues are probably located at (or near) the substrate-binding site while the sulfhydryl groups are located at a site other than the substrate binding region.     

Isolation and characterization of an acidophilic, heterotrophic bacterium capable of oxidizing ferrous iron.

A heterotrophic bacterium, isolated from an acidic stream in a disused pyrite mine which contained copious growths of "acid streamers," displayed characteristics which differentiated it from previously described mesophilic acidophiles. The isolate was obligately acidophilic, with a pH range of 2.0 to 4.4 and an optimum pH of 3.0. The bacterium was unable to fix carbon dioxide but oxidized ferrous iron, although at a slower rate than either Thiobacillus ferrooxidans or Leptospirillum ferrooxidans. Elemental sulfur and manganese(II) were not oxidized. In liquid media, the isolate produced macroscopic streamerlike growths. Microscopic examination revealed that the bacterium formed long (greater than 100 microns) filaments which tended to disintegrate during later growth stages, producing single, motile cells and small filaments. The isolate did not appear to utilize the energy from ferrous iron oxidation. Both iron (ferrous or ferric) and an organic substrate were necessary to promote growth. The isolate displayed a lower tolerance to heavy metals than other iron-oxidizing acidophiles, and growth was inhibited by exposure to light. There was evidence of extracellular sheath production by the isolate. In this and some other respects, the isolate resembles members of the Sphaerotilus-Leptothrix group of filamentous bacteria. The guanine-plus-cytosine content of the isolate was 62 mol%, which is less than that recorded for Sphaerotilus-Leptothrix spp. and greater than those of L. ferrooxidans and most T. ferrooxidans isolates.     

Phosphorylation of a nonhistone protein fraction which coextracts with the high-mobility-group proteins of chromatin

³²P-labelled chromatin proteins from rat liver and ventral prostate were fractionated according to the procedure designed to enrich high-mobility-group (HMG) nonhistone proteins. This fraction, however, reproducibly demonstrated small amounts of apparently basic nonhistone proteins other than HMG nonhistone proteins. These proteins appeared to be tissue specific and were highly labelled with ³²P. The ³²P-labelled phosphoproteins were soluble in trichloroacetic or perchloric acid, migrated in acid-urea polyacrylamide gels, and demonstrated pI values ranging from 6.8 to 7.5. The HMG proteins 1 and 2 showed no incorporation of radioactivity under these experimental conditions.     

Conformation and activity of chloroplast coupling factor exposed to low chemical potential of water in cells.

(1) Photophosphorylation, Ca2+-ATPase and Mg2+-ATPase activities of isolated chloroplasts were inhibited 55--65% when the chemical potential of water was decreased by dehydrating leaves to water potentials (psi w) of --25 bars before isolation of the plastids. The inhibition could be reversed in vivo by rehydrating the leaves. (2) These losses in activity were reflected in coupling factor (CF1) isolated from the leaves, since CF1 from leaves with low psi w had less Ca2+-ATPase activity than control CF1 and did not recouple phosphorylation in CF1-deficient chloroplasts. In contrast, CF1 from leaves having high psi w only partially recoupled phosphorylation by CF1-deficient chloroplasts from leaves havig low psi w. This indicated that low psi w affected chloroplast membranes as well as CF1 itself. (3) Coupling factor from leaves having low psi w had the same number of subunits, and the same electrophoretic mobility, and could be obtained with the same yields as CF1 from control leaves. However, direct measurements of fluorescence polarization, ultraviolet absorption, and circular dichroism showed that CF1 from leaves having low psi w differed from control CF1. The CF1 from leaves having low psi w also had decreased ability to bind fluorescent nucleotides (epsilon-ATP and epsilon-ADP). (4) Exposure of isolated CF1 to low psi w in vitro by preincubation in sucrose-containing media inhibited the Ca2+-ATPase activity of the protein in subsequent assays without sucrose. Inclusion of 5 or 10 mM Mg2+ in the preincubation medium markedly inhibited Ca2+-ATPase activity. (5) These results show that CF1 undergoes changes in cells which alter its phosphorylating ability. Since low cell psi w changed the spectroscopic properties but not other protein properties of CF1, the changes were most likely caused by altered confurn, photophosphorylation. The inhibition of ATPase activity in CF1 in vitro at low psi w and high ion concentration mimicked the change in activity seen in vivo.     

Release of chemical mediators from partially purified human lung mast cells.

Human lung mast cells dispersed by enzymatic digestion of human lung fragments were concentrated to greater than 50% purity by sedimentation in isopycnic and velocity gradients. The dispersed lung mast cells had a characteristic ultrasturctural appearance including granules with a scroll or reticular structural appearance including granules with a scroll or reticular structure surrounded by perigranular membranes. Histamine and preformed eosinophilotactic activity sedimented with mast cells on isopycnic gradients, and mast cells and these mediators were separated from the bulk of the other lung cells after velocity gradient sedimentation. The histamine content of isolated lung mast cells was calculated to range from 1.0 to 5.5 pg/cell. The quantity of SRS-A generated with anti-IgE or specific antigen was relatively limited but confined to the mast cell-rich fractions and associated with release of histamine and eosinophilotactic activity.     

Seasonal physiological responses of Argania spinosa tree from Mediterranean to semi-arid climate

Argania spinosa (the argan tree) is a slow-growing tree endemic of Morocco, growing on semi-arid areas where no other tree species can live. With the aim of predicting temporal changes in A. spinosa woodlands under a probable increase in aridity, we set off to investigate these questions: how do A. spinosa physiological attributes respond to variations in climatic conditions and seasonality, and which is the set of attributes that most affects tree response to environmental conditions? In three study sites, Beni Snassen (North), High-Atlas (Mountain) and Admine Forest in Agadir (Coastal), gas exchange measurements, photochemical efficiency, leaf water potential and different leaf attributes were monitored in February, July and November of 2006. The Mountain site presents the most continental climate. Trees in this site were the most stressed in summer, having the lowest midday leaf water potential values, photochemical efficiency and assimilation rates. We found a Ψ_md threshold around -4 MPa, below which stomatal conductance responds linearly to Ψ_md. Plants from the North area never reached this threshold during the study period. Although leaf pigments presented a clear seasonal pattern, leaves from Coastal trees exhibit the highest content for each season. The three study sites were separated by two discriminate functions obtained by canonical discriminant analysis. In summer, the Mountain population is separated from the other sites mainly by assimilation rate and F_v/F_m, while in winter transpiration rates and chlorophyll content are the main discriminant variables. Our study shows that A. spinosa trees adjust their physiological status and leaf attributes to environmental conditions allowing plants to thrive under a dry climate. Under a scenario of global change, the distribution of the argan tree likely shifts to milder areas.     

Nitrogen metabolism in tomato seedlings

Tomato seedlings absorbed increasing amounts of nitrate-N. The total uptake was doubled as the concentration of nitrate was quadruplicated. NO₃?N absorption seemed to be accompanied by efflux of OH^? ions which shift the pH of the media to the alkaline side. A minor fraction of the absorbed nitrate accumulated in the tissues while the major part was assimilated into peptides and proteins. The dry matter gain was by the end of experiment relatively higher than the control samples raised on nitrogen-free nutrient solution. Nitrate assimilation seemed to involve its reduction down to ammonia level. Since neither nitrite nor ammonia was recovered in the tissue-medium system, it was postulated that the rate of reduction was slower than the rate of product assimilation. The first step in nitrate reduction (nitrate→nitrate) appeared to be limiting while further reduction steps occurred rapidly and accompanied by simultaneous assimilation of ammonia. The enzyme responsible for the first step of nitrate reduction,i.e., nitrate reductase, was extracted from tomato shoots and roots. The activity in root extract amounted to about 30% of that of the shoot. This may suggest the localization of nitrate reduction in the leaves and realizes the relation between nitrate metabolism and photosynthesis.