Molecular basis for the special properties of proteins and enzymes from Halobacterium marismortui

Abstract Three proteins from Halobacterium marismortui , malate dehydrogenase (hMDH), glutamate dehydrogenase (hGDH) and ferredoxin (hFD) were purified and characterized with respect to their molecular masses, amino acid composition and, for hFD only, primary structure. Striking features of halophilic proteins are: the high excess of acidic over basic residues; acidic clusters in the sequence. Low-salt concentration causes inactivation and changes in structural parameters of hMDH and hGDH. Reactivation of hMDH involves long-lived stable intermediates. The salt concentration optimum of enzymic activity is independent of salt nature. The high capacity of halophilic proteins to retain water and salt is due to unique molecular properties, studied by physico-chemical techniques.     

Kinetics of 5-enolpyruvylshikimate-3-phosphate synthase inhibition by glyphosate

The herbicide glyphosate (N-phosphonomethyl glycine) is a potent reversible inhibitor of the 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase activity of the purified arom multienzyme complex from Neurospora crassa. Inhibition of the EPSP synthase reaction by glyphosate is competitive with respect to phosphoenolpyruvate, with K(i) 1.1 microM, and uncompetitive with respect to shikimate-3-phosphate. The kinetic patterns are consistent with a compulsory order sequential mechanism in which either PEP or glyphosate can bind to an enzyme: shikimate-3-phosphate complex.     

Bacterioplankton in the acidified Lake Gårdsjön

Total bacterial numbers in different strata of lake water and in inlet and outlet streams have been recorded during a yearly cycle. A calculated mean cell volume of 0.342 µm² has then been used to estimate bacterial biomass in the lake. Change of biomass during the year was substantial and the range was from about 0.1 g · m^–3 to about 1.0–1.2 g · m^–3. The seasonal development included a spring-early summer increase followed by a decrease to the minimum in July–August. Correlation between epi- and hypolimnion was high and in both strata two dominant autumn peaks in biomass appeared. With the exception of the last autumn peak the development of bacterial biomass was closely related to development of phytoplankton biomass and production.     

Water deficit enhancement of proline and α-amino nitrogen accumulation in potato plants and its association with susceptibility to drought

Potato plants ( Solanum tuberosum L. cvs 'Up-to-Date', 'Desiree', 'Alpha', 'Spunta', 'Elvira' and 'Troubadour') were exposed to cycles of water stress and relief during growth. Severe water deficit induced increased proline content 6- to 7-fold in nonturgid leaves which just started to wilt, and 8- to 27-fold in fully wilted leaves of potatoes. However, proline content was not affected during the early stages of stress development over a range of osmotic potentials in the leaves. The rising proline content was related to turgor loss of leaves independent of changes in the osmotic potentials, which indicates that proline involvement in osmoregulation of potato leaves is unlikely.
Repeated cycles of water stress and relief resulted in increased proline and α-amino nitrogen content in the tuber tissue of some of the cultivars. The smallest increase in proline content was obtained in 'Alpha' tubers and the content of α-amino nitrogen remained unaffected by the water stress. Concomitantly, 'Alpha' was the most drought-tolerant cultivar, as determined by its capacity to accumulate dry matter in tubers under stress conditions. On the other hand, in tubers of cultivars which were more susceptible to drought, a marked increase in proline and α-amino nitrogen was observed in response to water stress. The possible association of these findings with tolerance of potatoes to repeated short periods of drought is discussed.     

Nutrition of winter wheat during the life cycle. I. Yield and accumulation of dry matter and minerals

Mineral uptake by winter wheat (Trilicum aestivum L. cv. Martonvasari 8) was studied throughout the life cycle. Accumulation of macronutrients (i.e. total nitrogen, phosphorus, potassium, sodium, magnesium and calcium) and the water content of roots and shoots of plants grown in complete nutrient solution were higher than those of plants grown in two types of soils. The supply of macronutrients was in some cases limiting for soil-grown plants as revealed by a comparison of available and accumulated amounts of these nutrients. Their supply was abundant, however, for solution-grown plants. This led to a doubling of grain yield for the latter plants with a three fold increase in accumulation of dry matter and a five-fold increase in fresh weight. The efficiency ratios of solution-grown plants to soil-grown plants were approximately 1 for N and Na, 0.5 for Mg and Ca, and 0.3 for P and K.     

The effect of soil water status on critical phosphorus concentrations inStylosanthes hamata cv. Verano

Summary The effect of soil water status on the critical phosphorus concentration (CPC) determined in apices and whole tops ofStylosanthes hamata cv. Verano was investigated in a glasshouse trial. The species was grown with six rates of P and three ranges of soil water potential and was harvested at 10 and 14 weeks after germination. The CPC of both whole tops and apices decliced between the two harvests. At the first harvest the CPC of both whole tops and apices increased as the soil water potential decreased but at the second harvest there was no effect of soil water potential on CPC. It is suggested that at the earlier harvest water stress was delaying physiological development, resulting in a CPC characteristic of chronologically younger tissue, but that by the second harvest the decline in CPC with age had ceased for all water treatments.     

Secondary structure features of ribosomal RNA species within intact ribosomal subunits and efficiency of RNA-protein interactions in thermoacidophilic (Caldariella acidophila,Bacillus acidocaldarius) and mesophilic (Escherichia coli) bacteria

Ribosomal subunits of Caldariella acidophila (max.growth temp., 90°C) have been compared to subunits of Bacillus acidocaldarius (max. growth temp., 70°C) and Escherichia coli (max. growth temp., 47°C) with respect to (a) bihelical content of rRNA; (b) G·C content of bihelical domains and (c) tightness of rRNA-protein interactions. The principal results are as follows. 1. Subunits of C. acidophila ribosomes (T_m = 90–93°C) exhibit considerable thermal tolerance over their B. acidocaldarius (T_m = 77°C) and E. coli counterparts (T_m = 72°C). 2. Based on the ‘melting’ hyperchromicities of the intact ribosomal subunits a 51–55% fraction of the nucleotides appears to participate in hydrogen-bonded base pairing regardless of ribosome source, whereas a larger fraction, 67–70%, appears to be involved in hydrogen bonding in the naked rRNA species. 3. The G·C content of bihelical domains of both free and ribosome-bound rRNA increases with increasing thermophily; based on hyperchromicity dispersion spectra of intact subunits and free rRNA, the bihelical parts of C. acidophila rRNA are estimated to contain 63–64% G·C, compared to 58.5% G·C for B. acidocaldarius and 55% G·C for E. coli. 4. The increment in ribosome T_m values with increasing thermophily is greater than the increase in T_m for the free rRNA, indicating that within ribosomes bihelical domains of the thermophile rRNA species are stabilized more efficiently than their mesophile counterparts by proteins or/ and other component(s). 5. The efficiency of the rRNA-protein interactions in the mesophile and thermophile ribosomes has been probed by comparing the releases, with LiCl-urea, of the rRNA species from the corresponding ribosomal subunits stuck to a Celite column through their protein moiety; it has been established that the release of C. acidophila rRNA from the Celite-bound ribosomes occurs at salt-urea concentrations about 4-fold higher than those required to release rRNA from Celite-bound E. coli ribosomes. 6. Compared to E. coli, the C. acidophila 50 and 30 S ribosomal subunits are considerably less susceptible to treatment designed to promote ribosome unfolding through depletion of magnesium ions.     

High-frequency1H NMR studies of the effects of growth factors and phorbol esters on normal syrian hamster diploid fibroblast cells

The nuclear magnetic resonance (NMR) parameters, spin-lattice (T₁), and spin-spin (T₂) relaxation time, are usually longer for neoplastic cells than for normal cells of the same cell type. This has generally been true at low NMR frequencies (≤100 MHz) when comparisons have been made between normal and neoplastic cells that have both spent a short time in culture. We have previously demonstrated that although the T₁ values of paired normal and neoplastic Syrian hamster (SH) fibroblastic cells in culture are not significantly different when measured at 300 MHz, the 300 MHz T₂ values for the neoplastic cells are smaller than those of the normal cells. (Xin et al. (1986),Cell Biophysics 8, 213.) Since treatment of normal diploid cells with polypeptide growth factors or tumor promoters frequently results in reversible expression of neoplasia-associated phenotypes, T₁ and T₂ were obtained at 300 MHz for treated and untreated SH cells to see if these compounds could also produce smaller 300 MHz T₂ values. Secondary culture SH fetal fibroblast cells were treated with epidermal growth factor (EGF), fibroblast growth factor (FGF), phorbol-12,13-didecanoate (PDD) and 4-α-phorbol-12,13-didecanoate (4αPDD). Treatment with either growth factor resulted in smaller T₂ values, but a statistically significant decrease was not observed for PDD or 4αPDD. The observed reductions in T₂ values were correlated with the morphological and growth-stimulatory effects of these compounds on the cells.     

Coccidian Parasites (Apicomplexa: Eimeriidae) of Nerodia spp. (Serpentes: Colubridae), with a Description of a New Species of Eimeria

Eimeria conanli n. sp. (Apicomplexa: Eimeriidae) is described from intestinal contents and feces of Nerodia erythrogaster transversa and N harteri harteri from northcentral Texas. Oocysts of the new species are ellipsoid in shape. 17.9 × 13.0(15–21 × 12–15) μm, with a smooth, thin, single-layered wall; shape index 1.4 (1.2–1.5). One to several (usually 2) polar granule(s) and an oocyst residuum are present, but a micropyie is absent. Sporocysts are elongate, 12.9 × 5.2 (13–15 × 5–6) -m, apparently without a true Stieda body structure. Each sporoeyst contains an ellipsoid residuum, 3.9 × 3.2 (3–6 × 2–4) μm, and elongate sporozoites, 11.4 × 2.5 (10–14 × 2–3) μm in situ, each with a spherical or subspherical anterior refractile body and spherical to ellipsoid posterior refractile body. In addition to the new species, oocysts of 4 previously described eimerians from colubrid snakes were found in these hosts.