Changes in fatty acid distribution and thermotropic properties of phospholipids following phosphatidylcholine depletion in a choline-requiring mutant of Neurospora crassa

Growth of a choline requiring auxotroph of Neurospora crassa on medium lacking exogenous choline produces large changes in the levels of phosphatidylethanolamine and phosphatidylcholine. Whole cell fatty acid distributions were found to vary widely between different phospholipid species of normally growing, choline-supplemented cultures with phosphatidylcholine showing the highest levels of unsaturation and anionic phospholipids and cardiolipin having the lowest. In these lipids, choline deprivation produced little change in fatty acid profiles of phosphatidylethanolamine, whereas changes in fatty acids of phosphatidylcholine and acidic phospholipids resulted in increased levels of unsaturation at both growth temperatures. Microsomal phospholipids also showed fatty acid variability with sharp decreases in phosphatidylcholine unsaturates and increases in acidic phospholipid unsaturated fatty acids at low growth temperatures. Fluorescence polarization of 1,6-diphenylhexatriene in vesicles formed from total cellular and microsomal lipids showed that choline deprivation produces changes in thermotropic properties in the lipids in deprived cultures at either growth temperature. The effective differences in fluorescence polarization between choline-deprived and supplemented cultures grown at a given temperature were found to be comparable to those produced by temperature acclimation in normally growing cultures over a temperature range of 22 K.     

The fate of nitrogen (15N) released from different plant materials during decomposition under field conditions

Release of N, retention in soil, availability to a subsequent crop and total recovery of N derived from different¹⁵N-labelled plant materials decomposing in soil was investigated in two field experiments. In the first experiment five different plant species (white clover, red clover, subterranean clover, field bean and timothy) and in the second subterranean clover of different maturity (2,3 and 4 months old) were buried in mesh bags in the soil and allowed to decompose for 10 and 4 months, respectively. Most of the N released from the decaying plant materials was retained in the soil (27–46% of input). The subsequent crop (barley) took up 6–25% of input. The uptake correlated with the amount of N released from the decomposing material (r=0.936^*, I experiment). Similar amounts of subterranean clover N were taken up by barley regardless to whether the material was buried in soil in the previous autumn or just before sowing of the crop. At the end of the experiments, the total recovery of the introduced plant-derived N varied between 89 and 102%. The results present evidence that the ability of the soil to retain plant-derived N is strong in comparison with the ability of the subsequent crop and different loss mechanisms to remove it.     

The effect of sodium chlorate and nitrapyrin on the nitrification mediated nitrosation process in soils

Summary The influence of total nitrification to nitrate or partial nitrification to nitrite on the soil organic nitrogen status was examined. NH ₄ ⁺ –¹⁵N was added to the soil in the absence and the presence of NaClO₃, respectively nitrapyrin. The first chemical inhibits only nitrate formation, the second inhibits total nitrification. The accumulation of nitrite nitrogen in the soil at levels up to 5 mg kg^–1 increased the loss of nitrogen. Yet, it did not increase the binding of mineral nitrogen into soil organic matter, relative to the control soil. The data suggest that the biochemistry of the nitrite formation process, rather than the levels of nitrite ions formed, are of primary importance in the role of nitrification mediated nitrosation of soil organic matter.     

Subcellular localization of enterokinase (Enteropeptidase EC 3.4.21.9) in rat small intestine

The subcellular localization of enterokinase is controversial. In this study, enterokinase was extracted from a soluble fraction and a brush border fraction of rat small intestine by differential centrifugation. The soluble fraction contained 41% of the initial enterokinase activity while the brush border fraction contained only 4.6% of the initial activity. In contrast, alkaline phosphatase monitored as a brush border marker, yielded 26.3 in the brush border fraction and only 6% in the soluble fraction. Further separation of the soluble fraction on a Sepharose 4B column revealed three peaks of enterokinase activity. One small peak (3%) of a bound enzyme (M_r, 2·10^?6) and two larger peaks of free enzyme (M_r, 3·10⁵ and 9·10⁵). In contrast, alkaline phosphatase major fraction was in a high molecular weight peak of bound enzyme. When the brush border fraction was chromatographed only a single peak of bound enterokinase and alkaline phosphatase were found. In the lower part of the small intestine, no brush border-bound enterokinase was found, while the peak of alkaline phosphatase was the same as in the upper intestine. These data suggest that enterokinase activity in the rat intestine is mainly in a free form localized in the mucin and soluble fraction and to a negligible extent in the brush border.     

In vitro growth of murine T cells. IV. Use of T-cell growth factor to clone lymphoid cells

Murine bone marrow cells can suppress the in vitro primary antibody response of normal spleen cells without apparent cytotoxicity. The bone marrow cells suppress the response to both T-dependent (SRBC) and T-independent (DNP-Ficoll) antigens. When bone marrow cells are fractionated on a sucrose density gradient, the suppressive activity is found in the residue rather than the lymphocyte fraction. The suppressive activity is either unaffected or enhanced by treatment with anti-T- and anti-B-cell serums. Pretreatment of mice with phenylhydrazine which reduces the number of pre-B cells did not reduce the suppressive activity of their bone marrow cells. Suppressive activity is abolished by irradiation of the marrow cells in vitro with 1000 R prior to assay. The activity is present in the marrow of thymus deficient (nude) mice, infant mice, and mice which have been made polycythemic by transfusion. Furthermore, the suppressor cell can phagocytize iron carbonyl particles, is slightly adherent to plastic and Sephadex G-10, and can bind to EA monolayers. We conclude that the suppressor cell is not a mature lymphocyte or granulocyte nor a member of the erythrocytic series, but is likely to be an immature cell possibly of the myeloid series. We speculate on the physiologic role of this cell.     

DasFestuca vivipara-Problem in den Alpen

The differences betweenFestuca vivipara (tetraploid) andF. ovina subsp.supina (diploid), two often confused taxa, are demonstrated in regard to morphology, leaf anatomy, ecology and distribution. New maps illustrate the distribution ofF. vivipara in the Alps and the Northern Hemisphere. The development of different polyploidy levels withinF. vivipara as a consequence of occasional sexual processes is discussed. (English Summary on p. 39.)

     

Leaching losses of nitrogen from a clay soil under grass and cereal crops in Finland

Summary A 16-plot experimental field was established in 1975 on a clay soil in Jokioinen, Finland. The water discharge through tile drains was measured and its ammonium and nitrate N contents determined for each plot separately. The surface runoff was also measured and analysed. The annual runoff and the N leached from the surface of moderately fertilized (100 kg/ha/y N) cereal plots varied during 1976–1982 from 21 to 301 mm and from 2 to 7 kg/ha, respectively. The discharge of water and leaching of N through subdrains varied from 65 to 225 mm and from 1 to 38 kg/ha, respectively. The highest leaching was probably caused by a previous fallow. The annual N uptake by the crop varied between 41 and 122 kg/ha.Of the fertilizer-N used for cereals, 20% of that applied in the autumn was lost, but only 1 to 4 per cent was lost when applied in the spring. There was much less N leaching from ley than from barley plots, although the former was given twice as much N. The rate of N fertilization had only a very slight effect on N leaching from both ley and barley plots.The results were compared with those obtained in lysimeters filled with clay, silt, sand and peat soils. No definite conclusions can be drawn because the lysimeter experimental data are only for the first year.     

Aza-β-amino acid containing peptidomimetics as cAMP-dependent protein kinase substrates

Peptidomimetic analogs of the peptide RRASVA, known as the “minimal substrate” of the catalytic subunit of the cAMP-dependent protein kinase (PKA), were synthesized by consecutive replacement of natural amino acids by their aza-β³ analogs. The peptidomimetics were tested as PKA substrates and the kinetic parameters of the phosphorylation reaction were determined. It was found that the interaction of these peptidomimetics with the enzyme active center was sensitive to the location of the backbone modification, while the maximal rate of the reaction was practically not affected by the structure of substrates. The pattern of molecular recognition of peptidomimetics was in agreement with the results of structure modeling and also with the results of computational docking study of peptide and peptidomimetic substrates with the active center of PKA. It was concluded that the specificity determining factors which govern substrate recognition by the enzyme should be grouped along the phosphorylatable substrate, and such clustering might open new perspectives for pharmacophore design of peptides and peptide-like ligands.