Influence of temperature and nitrogen concentration on photosynthesis ofDunaliella viridis Teodoresco

The photosynthetic behaviour ofDunaliella viridis has been studied under a combination of three variables: irradiance (0–900 mol m^–2 s^–1), temperature (15, 23, 31, 38, 42 °C) and nitrogen concentration (0.05, 0.5, 1.5, 5, 10 mM NO ₃ ^- ) at a salinity of 2 M NaCl.The highest rates of photosynthesis have been found at 31 °C and a nitrate concentration of 10 mM. There exists a synergistic effect between temperature and nitrogen availability on the photosynthesis ofD. viridis; under nitrogen deficiency oxygen evolution is low, even null at high temperature. The interaction between these two variables of control occurs in a multiplicative way. There is also a general increase in photosynthetic pigments following the increase in nitrogen concentration in the culture medium. The normalization of net photosynthesis data in relation to chlorophylla shows that nitrogen concentration makes an indirect control of the photosynthetic rate ofD. viridis through the variation of pigment concentration.     

Pericentric inversion of chromosome 19 in three families

Summary Pericentric inversion of chromosome 19 has been found in several members of three unrelated families from a restricted geographical region. In one of the families, an additional pericentric inversion of chromosome 9 was observed. Reproductive problems, multiple abortions in two families and a neonatal death in the third, were present. A review of previously described cases is included, and the genetic risk connected with this type of rearrangement is also discussed.     

Mitogenic,immunoadjuvancy, and genetic studies on fatty acyl maltose

Summary Three synthetic glycolipids, maltose tetrapalmitate (MTP), maltose hexastearate (MHS), and maltose hexalinoleate (MHL) prepared as nontoxic lipid A analogs, and Escherichia coli lipopolysaccharide (LPS) were assayed for their mitogenic activity using spleen lymphocytes in nine inbred mouse strains and three F1 hybrids. The MTP and LPS were also assayed for their ability to enhance plaque-forming cell (PFC) responses using sheep red blood cells as the antigen in th same inbred mouse strains and F1 hybrids, The mitogenic activity of synthetic glycolipids was several fold lower than that of LPS and MHL was inferior to MTP and MHS. DBA/2J was the most responsive strain for MTP and DBA/1J and C3H/HeJ the least. The mitogenic activity of MTP was generally in agreement with the PFC response stimulation by it. Lowdose cyclophosphamide treatment of mice synergized MTP for PFC response augmentation. Genetic studies on MTP mitogenicity revealed that 90% of responder DBA/2J X nonresponder C3H/HeJ F1 hybrids had intermediate mitogenic activity. Among F2, 73% had intermediate-high activity and 27% were nonmitogenic. Among F1 X C3H/HeJ backcrosses 11% had high, 56% intermediate, and 33% had no mitogenic activity, whereas, for the F1 X DBA/2J backcross, 14% had high, 36% intermediate, and 50% low or negligible activity. The data favored a single gene for MTP activation of immune cells.This work was supported, in part, by a grant from the National Cancer Institute of Canada, and by grant from the Cancer Research Society Inc.     

The heat shock response in meso- and thermoacidophilic chemolithotrophic bacteria

Abstract The heat shock response was studied in a chemolithotrophic thermoacidophilic archaebacterium Sulfolobus acidocaldarius (shifted from 70° to 85°C) and a mesoacidop0ilic microorganism Thiobacillus ferrooxidans (from 30° to 41°C). When transferred from their normal growth temperature to the stress temperature, cells showed a decrease in the incorporation of Na₂¹⁴CO₃ into proteins, and at the same time, the synthesis of a specific subset of heat shock proteins was observed. Ethanol (4%) at 30°C, also caused a response similar to the heat shock upon T. ferrooxidans cells, whereas Sulfolobus cells at 70°C did not incorporate radioactive CO₂ in the presence of ethanol, apparently being damaged by the organic solvent.     

DNA-methyltransferase activities in Streptomyces antibioticus

Abstract To quantitate ammonia production by the intestinal flora, ammonia levels in arterial blood and the venous effluent of the small and large bowel of conventional, selectively decontaminated, germ-free and gnotobiotic rats were measured.
When the anaerobic flora was removed by decontamination a significant decrease in ammonia levels was observed in the effluent of both the small and large intestine. Decontamination of aerobic flora did not result in depression of ammonia production. Gnotobiotic rats colonised with an anaerobic flora or with a mixed aerobic and anaerobic flora, showed a slight increase in ammonia levels. No increase in ammonia production was observed when rats were colonised with aerobic flora. These results indicate that the Enterobacteriaceae were not responsible for ammonia generation.
The increase in ammonia levels after colonisation with anaerobic or mixed anaerobic/aerobic flora did not completely restore ammonia levels, despite reaching bacterial counts which were comparable to those in conventional rats. This may be explained by the limited number of species with which the rats were colonized. The finding that aerobic flora does not significantly contribute to ammonia production suggests that neomycin, known to be exclusively effective against aerobic flora, must have other effects to explain improvement of hepatic encephalopathy.     

Sequence of the human erythrocyte phosphoglycerate mutase by microsequencer and mass spectrometry

We have previously reported the isolation in pure form of the human erythrocyte phosphoglycerate mutase isozyme B. We now report the sequence of the whole protein and the identification of its N-terminal blocking group. The protein tryptic peptides of phosphoglycerate mutase isozyme B were isolated by high performance liquid chromatography and their sequence determined by microsequencing. The sequence and the nature of the blocking group of the N-terminal tryptic peptide was shown to be N-acetyl-Ala-Ala-Tyr-Lys by mass spectrometry. Overlaps of the tryptic peptides were obtained by studying the V8 Staphylococcus aureus protease peptides of the aminoethylated phosphoglycerate mutase isozyme B either by microsequencing or by mass spectrometry. The procedure used allowed us to obtain the sequence on a very small amount of material and in a short period of time. Our data agree well with those derived from the cDNA nucleotide sequence described by Sakoda et al. (Sakoda, S., Shanske, S., DiMauro, S., and Schon, E. A. (1988) J. Biol. Chem. 263, 16899-16905). In addition, our data directly indicate that the initiation codon does not introduce a methionine as N-terminal amino acid and allowed the identification of the acetyl N-terminal group.     

Effects of phosphorylation, MgATP, and ionic strength on the rates of papain degradation of heavy and light chains of smooth muscle heavy meromyosin at the S1-S2 junction

The effects of ionic strength, MgATP, and phosphorylation on the degradation rates of heavy meromyosin (HMM) by papain have been compared to their effects on the sedimentation coefficient (s20,w) to determine the relationship of the degradation rate to the equilibrium between the flexed and the extended forms (Suzuki, H., Stafford, W. F., Slayter, H. S., and Seidel, J. C. (1985) J. Biol. Chem. 260, 14810-14817). At 0.025 M NaCl, where HMM is predominantly in the flexed form, MgATP, Mg-adenylyl imidodiphosphate or MgADP reduce kH by 80-90%. MgATP exerts its optimal effect at this ionic strength, where at least 70% of HMM is flexed in the presence or absence of MgATP, suggesting that nucleotides reduce kH by decreasing the proteolytic susceptibility of the flexed form. At 0.5 M NaCl, where HMM is in the extended form, MgATP has no effect on kH. At low ionic strengths phosphorylation decreases kH but increases it in the presence of MgATP. Plots of kH against s20,w determined at various ionic strengths are linear, the data for phosphorylated and dephosphorylated HMM falling on the same line. Thus, raising the ionic strength or phosphorylating the 20-kDa light chain appears to alter kH by increasing the fraction of HMM in the extended form. The degradation rate of the 20-kDa light chain (kL) of dephosphorylated HMM responds to changes in ionic strength in essentially the same way as does kH, suggesting that the response of kL to changes in ionic strength can also be attributed to conversion of HMM to the extended form. However, kL for phosphorylated HMM measured in the presence of MgATP exhibits very little dependence on ionic strength.     

Electrogenic behavior of the human red cell Ca2+ pump revealed by disulfonic stilbenes

Summary A systematic study was made of the action of 4-acetamido-4-isothiocyanostilbene-2,2-disulfonic acid (SITS) and 4,4-diisothiocyanostilbene-2,2-disulfonic acid (DIDS) on active Ca²⁺ transport of human erythrocytes. Pumping activity was estimated in inside-out vesicles (IOV's) by means of Ca²⁺-selective electrodes or use of tracer⁴⁵Ca²⁺. The stilbenes exhibited an approximately equal inhibitory potency and their action could be overcome by carbonyl cyanidep-trifluoromethoxyphenylhydrazone (FCCP) at low but not at high stilbene concentrations. In the absence of DIDS. Ca²⁺ transport was not affected upon addition of valinomycin, but it was appreciably reduced when vesicles were preincubated with low DIDS concentrations. Such an effect was strictly dependent on the external K⁺ concentration and it was abolished when valinomycin was added together with FCCP. Similar results were obtained using IOV's prepared from intact cells which had been previously exposed to the stilbene. The findings clearly demonstrate the presence in human red cells of a partially electrogenic Ca²⁺ pump, exchanging one Ca²⁺ ion for one proton.     

Phosphate sequestration by glycerol and its effects on photosynthetic carbon assimilation by leaves

Glycerol induced a limitation on photosynthetic carbon assimilation by phosphate when supplied to leaves of barley (Hordeum vulgare L.) and spinach (Spinacia oleracea L.). This limitation by phosphate was evidenced by (i) reversibility of the inhibition of photosynthesis by glycerol by feeding orthophosphate (ii) a decrease in light-saturated rates of photosynthesis and saturation at a lower irradiance, (iii) the promotion of oscillations in photosynthetic CO₂ assimilation and in chlorophyll fluorescence, (iv) decreases in the pools of hexose monophosphates and triose phosphates and increases in the ratio of glycerate-3-phosphate to triose phosphate, (v) decreased photochemical quenching of chlorophyll fluorescence, and increased non-photochemical quenching, specifically of the component which relaxed rapidly, indicating that thylakoid energisation had increased. In barley there was a massive accumulation of glycerol-3-phosphate and an increase in the period of the oscillations, but in spinach the accumulation of glycerol-3-phosphate was comparatively slight. The mechanism(s) by which glycerol feeding affects photosynthetic carbon assimilation are discussed in the light of these results.Abbreviations Chl chlorophyll - C _i intercellular concentration of CO₂ - P phosphate - PGA glycerate-3-phosphate - Pi orthophosphate - triose-P sum of glyceraldehyde-3-phosphate and dihydroxyacetone phosphate     

Limitation of photosynthesis by changes in temperature

The aim of this work was to examine the effect of abrupt changes in temperature in the range 5 to 30°C upon the rate of photosynthetic carbon assimilation in leaves of barley (Hordeum vulgare L.). Measurement of the CO₂-assimilation rate in relation to the intercellular partial pressure of CO₂ at different temperatures and O₂ concentrations and at saturating irradiance showed that as the temperature was decreased photosynthesis was saturated at progressively lower CO₂ partial pressures and that the transition between the CO₂-limited and ribulose-1,5-bisphosphate-regeneration-limited rate became more abrupt. Feeding of orthophosphate to leaves resulted in an increased rate of CO₂ assimilation at lower temperatures at around ambient or higher CO₂ partial pressures both in 20% O₂ and in 2% O₂ and it removed the abruptness in the transition between the CO₂-limited and ribulose-1,5-bisphosphate-regeneration-limited rates. Phosphate feeding tended to inhibit carbon assimilation at higher temperatures. The response of carbon assimilation to temperature was altered by feeding orthophosphate, by changing the concentrations of CO₂ or of O₂ or by leaving plants in the dark at 4°C for several hours. Similarly, the response of carbon assimilation to phosphate feeding or to changes in 2% O₂ was altered by leaving the plants in the dark at 4°C. The mechanism of limitation of photosynthesis by an abrupt lowering of temperature is discussed in the light of the results.Abbreviations A rate of CO₂ assimilation - P _i intercellular partial pressure of CO₂ - RuBP ribulose-1,5-bisphosphate