Electrophoretic profiles of cyanobacterial membrane polypeptides showing heme-dependent peroxidase activity

The photosynthetic membranes of Anacystis nidulans R2 were examined electrophoretically following solubilization with lithium dodecyl sulfate. Electrophoresis yielded six prominent chlorophyll-containing bands. In addition, five polypeptides were observed which possessed heme-dependent peroxidase activity, monitored by incubating gels with 3,3′,5,5′-tetramethylbenzidine plus hydrogen peroxide. One such polypeptide, at 105 kdaltons, was removed by repeated washing of the membranes. Four remaining peroxidase-active polypeptides were observed at 7.2, 13.5, 18.5 and 33 kdaltons. Further examination of these four polypeptides yielded the following results. (1) The mobility of the 33 kdalton polypeptide was altered from 29 to 33 kdaltons upon heating (70°C) during membrane solubilization. (2) All four polypeptides showed stable heme-protein associations in the presence of 8 M urea; however, in the presence of urea, alterations in protein mobility were observed for each poly-peptide and only two (at 13.5 and 33 kdaltons) showed peroxidase activity following heating (70°C) during membrane solubilization. (3) The presence of thiols during membrane solubilization at 0°C was required to observe peroxidase activity at 7.2 kdaltons. These results, when compared to known properties of isolated cytochromes, suggest that the four polypeptides characterized here correspond to the subunits of photosynthetic cytochromes. Electrophoretic assessment of maize mutants lacking cytochrome f and b₆ activity supports this suggestion.     

The effects of extrahypothalamic cycloheximide on sexual receptivity in the rat

The present experiment was concerned with extrahypothalamic control of sexual receptivity. Cycloheximide, an inhibitor of protein synthesis, suppressed sexual receptivity in the steroid-primed ovariectomized rat when it was injected into the preoptic area. Cyclohexamide was without effect when injected into the cortical and medial nuclei of the amygdala, lateral septum or caudate nucleus.     

Suppressive effects of soluble histocompatibility antigens on the in vitro generation of cytotoxic T cells to D-end alloantigens

Murine histocompatibility antigens were solubilized from the spleens and lungs of C57BL/6 (H-2b) animals with hypertonic salt (3 M KC1). Aggregate-free soluble antigens were incubated with nonadherent lymph node cells from BALB/c (H-2d) mice for 18 hr prior to their use as responder cells in the mixed-lymphocyte reaction (MLR). It was found that the generation of cytotoxic cells was suppressed while the proliferative response was not affected. The observed suppression was not due to a shift in the kinetics of the generation of cytotoxicity as determined throughout a 10-day culture period. The suppression was specific in that the response in MLR to unrelated H-2f stimulator cells and the subsequent generation of cytotoxic cells were unchanged. Using various H-2 recombinant strains as target cells in the assay of cell-mediated lympholysis, suppression of cytotoxicity was observed when the D end, but not the K end, was shared with the C57BL/6 strain from which the antigens were derived.     

Inhibitory effect of cortisone acetate on the stimulation of rat liver cytosol l-serine Pyruvate aminotransferase by dibutyryl adenosine 3′,5′-monophosphate

An injection of cortisone acetate at a dose of 5 mg/100 g body weight concomitant with dibutryl cyclic AMP prevents the increase in the activity of rat liver cytosol serine aminotransferase (L-serine: pyruvate aminotransferase, EC 2.6.1.51) elicited by the nucleotide with a lag of about 2 h. If the glucocorticoid is given 2 h prior to the nucleotide inducer, the lag disappears. The inhibitory effect of cortisone acetate gradually decays and is no longer detectable 12 h following its administration. Theophylline, insulin and glucose at doses which affect significantly the level of tyrosine aminotransferase, have no effect on the level of serine aminotransferase and on the cortisone inhibition. The inhibitory effect of the glucocorticoid on the dibutyryl cyclic AMP-mediated increase in serine aminotransferase diminishes with the age of animals. Increase in the enzyme activity by a single dose of glucagon can also be inhibited by cortisone acetate and actinomycin D as in the case with dibutyrl cyclic AMP as an inducer. The possibility of the existence of a specific inhibitory factor which is formed in response to cortisone acetate is discussed.     

Ecology and biogeography of plant communities associated with the post Plio-Pleistocene relict Rhododendron ponticum subsp. baeticum in southern Spain

Aims Rhododendron ponticum L. is reputed to be a post Plio‐Pleistocene relict plant species with a disjunct distribution that comprises the Iberian Peninsula to the west and the Euxinian region plus some restricted Mediterranean areas to the east. We analysed the ecological range (of subsp. baeticum) in the western area (Aljibe Mountains, north of the Strait of Gibraltar) to understand the factors determining the present area limitation. Location Sierra del Aljibe, north of the Strait of Gibraltar (Iberian Peninsula). Methods We selected 20 riparian sites where R. ponticum is common, and compiled data on the ecological diversity of associated woody species and ferns. We established a 500‐m main transect in each site, along the stream or river course, in which we placed five 20‐m‐long plots at regular intervals. We recorded physiographic habitat features, woody plants and fern abundance, and the number of R. ponticum individuals. Results Rhododendron ponticum in southern Spain is restricted to riparian forests in acidic soils (pH 4.0–6.4), and is mainly found on the banks of inclined and enclosed streams. In our inventory we recorded 59 woody taxa and 12 ferns, with R. ponticum being the dominant species of the understorey (mean abundance 78.6%). The communities are characterized by a high incidence of the humid warm temperate element, both in number of species (18.8 ± 3.7 per site) and abundance; meanwhile, the presence of the modern Mediterranean element (mean number of species 3.4 ± 3.8 per site) appears to be favoured by disturbance. These ecological–historical groups of taxa also show distinct patterns of typological habit, frequency of endemism, infrageneric diversity and geographical range. Populations of R. ponticum are characterized by a very variable density of seedlings in many sites, and the virtual lack of juveniles. Main conclusions Riparian forests of the Aljibe Mountains constitute a refuge for R. ponticum where the species persists, but populations appear to be in decline. The narrow ecological range of R. ponticum in the area strongly contrasts with its wide amplitude in the eastern natural area, mainly the Euxinian region, where R. ponticum probably finds better conditions due to the environmental heterogeneity of the region, and the lack of a hot dry season.     

Long-term vegetation change in the Juncus squarrosus grassland at Moor House,northern England

Data from the long-term experiment on sheep grazing versus zero sheep grazing (i.e. in an enclosure) on the composition of the Juncus squarrosus grassland at the Moor House NNR are presented. The data have been analysed to assess change in (1) the abundance of individual species, (2) higher plant and bryophyte communities, and (3) vegetation structure. The higher plant data suggested that both the enclosed-and grazed plots were changing in the same direction, but the enclosed plot was moving much faster. The general tendency was towards a blanket bog vegetation dominated by Eriophorum vaginatum and Calluna vulgaris. Juncus squarrosus has declined very quickly in the enclosed plot, but there has also been a slower decline in the grazed one. A significant increase in Calluna vulgaris has occurred only in the enclosed plot. In contrast, the bryophyte data showed completely different successional trajectories in the two treatment plots.The vegetation structure changed markedly after release from grazing, with a decrease in phytomass, but increase in necromass in the lowest height strata. There was no noticeable change in structure over the 18 year period in the grazed plot.Particular problems found in this study were that some species either fluctuated widely in response, or changed in a curvilinear manner.     

Intra- and interspecific variation in body size ofProtohermes (Megaloptera: Corydalidae)

The life history of three populations ofProtohermes grandis and two populations ofProtohermes immaculatus (Megaloptera: Corydalidae) was compared. In general, the larvae lived in stream riffles for 2 years and the adults appeared in summer. Adult body size differed between these closely related species and also between the populations ofP. grandis. Dwarfism occurred inP. immaculatus, a species that is endemic to the small, isolated island, Amami Island. The population ofP. grandis on Yaku Island, located between Amami Island and the mainland Kyushu, had an intermediate body size between that ofP. immaculatus and the mainland population ofP. grandis. Despite being an insular population,P. grandis on Tsushima Island had a similar body size to mainlandP. grandis. In these populations with large adults, some larvae lived in the streams for 3 years. The size distribution of benthic animals, which are the prey available toProtohermes larvae, differed between the streams studied. The density of large prey was lowest on Amami Island, intermediate on Yaku Island, and highest on the mainland and Tsushima Island. Different size distributions of available prey may be caused by the differences of benthic fauna; most of Ecdyonuridae and Ephemerellidae (large mayflies) and Perlidae (large stoneflies) were not found on Amami and Yaku Islands. Thus, there is a tendency to dwarfism in the populations ofProtobermes inhabiting streams where the density of large prey is low.     

Plant community structure in relation to grazing and environmental changes along a north-south transect in the western Kalahari

Sixteen vegetation types were described from a north-south transect in the western Kalahari. Pronounced differences were found between communities on the nutrient poor red Kalahari sand, covering most of the area and those on fine soils and white calcareous sand. Syntaxa resulting from severe overgrazing by livestock were in most cases clearly distinguished from the less disturbed vegetation. The communities on red sand consisted mainly of shrub savanna dominated by perennial tufted grasses, whereas in the vegetation on calcareous material and on overgrazed land, forbs, dwarf shrubs and shrubs played a more important role. The major communities on red sand showed a clear geographical zonation roughly corresponding to the gradient in mean annual rainfall and its interannual variation. In the northern and central Kalahari these syntaxa were dominated by species of Sudano-Zambezian origin and in the southern Kalahari by species showing Karoo-Namib affinities.     

Temperature dependence of the rate constants of the Escherichia coli RNA polymerase-lambda PR promoter interaction. Assignment of the kinetic steps corresponding to protein conformational change and DNA opening

The kinetics of formation and of dissociation of open complexes (RPo) between Escherichia coli RNA polymerase (R) and the lambda PR promoter (P) have been studied as a function of temperature in the physiological range using the nitrocellulose filter binding assay. The kinetic data provide further evidence for the mechanism R + P in equilibrium I1 in equilibrium I2 in equilibrium RPo, where I1 and I2 are kinetically distinguishable intermediate complexes at this promoter which do not accumulate under the reaction conditions investigated. The overall second-order association rate constant (ka) increases dramatically with increasing temperature, yielding a temperature-dependent activation energy in the range 20 kcal (near 37 degrees C) to 40 kcal (near 13 degrees C) (1 kcal = 4.184 kJ). Both isomerization steps (I1----I2 and I2----RPo) appear to be highly temperature dependent. Except at low temperatures (less than 13 degrees C) the step I1----I2, which we attribute to a conformational change in the polymerase with a large negative delta Cp degrees value, is rate-limiting at the reactant concentrations investigated and hence makes the dominant contribution to the apparent activation energy of the pseudo first-order association reaction. The subsequent step I2----RPo, which we attribute to DNA melting, has a higher activation energy (in excess of 100 kcal) but only becomes rate-limiting at low temperature (less than 13 degrees C). The initial binding step R + P in equilibrium I1 appears to be in equilibrium on the time-scale of the isomerization reactions under all conditions investigated; the equilibrium constant for this step is not a strong function of temperature and is approximately 10(7) M-1 under the standard ionic conditions of the assay (40 mM-Tris . HCl (pH 8.0), 10 mM-MgCl2, 0.12 M-KC1). The activation energy of the dissociation reaction becomes increasingly negative at low temperatures, ranging from approximately -9 kcal near 37 degrees C to -30 kcal near 13 degrees C. Thermodynamic (van't Hoff) enthalpies delta H degrees of open complex formation consequently are large and temperature-dependent, increasing from approximately 29 to 70 kcal as the temperature is reduced from 37 to 13 degrees C. The corresponding delta Cp degrees value is approximately -2.4 kcal/deg. We propose that this large negative delta Cp degrees value arises primarily from the burial of hydrophobic surface in the conformational change (I1 in equilibrium I2) in RNA polymerase in the key second step of the mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)