Variation in the C:P ratio of suspended and settling seston and its significance for P uptake calculations

SUMMARY. 1. In 1981–84 limnocorral (LC) experiments were performed in Lake Lucerne. Switzerland, to manipulate the planktonic community by varying P fertilization and by removing large zooplankton (with a 95 μm screen).
2. The C:P ratios in both suspended and entrapped seston exceeded the 'ideal' C:P ratio of 106 proposed by Redfield, Ketchum & Richards (1963) when P was limiting algal growth.
3. P fertilization could decrease the sestonic C:P ratio to 106 only when P did not limit algal growth; P additions far exceeding the P loading of eutrophic lakes were necessary to obtain this situation.
4. Changes in epilimnetic C:P ratios were usually related to short- term changes in primary production, caused by variable in situ light conditions and turbulence, and subsequent variation in POC concentrations.
5. Entrapped seston in the 95 μm-filtered LCs showed C:P ratios slightly higher than those of suspended seston, indicating fast P release and slower C mineralization in the epilimnetic nutrient cycle.
6. Removing large crustacean zooplankton enhanced epilimnetic P mineralization, and C:P ratios of entrapped seston in the 95 μm-filtered LCs were increased.
7 Detritus formed a relatively high proportion of the seston and amounted to more than two-thirds of the measured POC concentration.
8. Calculations of algal P uptake using information on sestonic C:P ratios and ¹⁴C uptake rates are questionable, as long as detritus cannot be separated from algae and net carbon uptake cannot be accurately measured.     

Human lymphoblastoid cell lines secreting antibodies with restricted HLA specificity

Peripheral B lymphocytes obtained from three healthy individuals who had been immunized against peripheral blood lymphocytes from appropriate HLA-incompatible donors were transformed by the use of Epstein-Barr virus. The transformed blastoid B cells were repeatedly subcultured by means of cluster picking, and the HLA antibody-producing cultures were identified by testing the culture supernatants by means of the cytotoxicity assay, using the corresponding donor cells. Thus far, four cell lines that secrete cytotoxic HLA antibodies (MP1, 3, 4, and 5) have been established. Specific immunoabsorption experiments revealed that the antibody activity is carried by lambda-type IgM for MP1, by kappa-type IgM for MP3 and MP5, and by both for MP4. Specificity analysis of a panel of HLA-pretyped cells indicated that MP1 detects DQw2, whereas MP5 recognizes B7. The specificity of MP3 was similar to a DQ specificity termed DC5 (probably equivalent to TA10) but not the same. In the case of MP4, both of the lambda-type and kappa-type antibodies appeared to be directed toward new HLA class 11 determinants.Abbreviations used in this paper HLA human major histocompatibility - EBV Epstein-Barr virus - B-LCL Blymphoblastoid cell line - NA not absorbed - PBS phosphate-buffered saline - SPA Sepharose protein A - NRS normal rabbit serum     

The role of the cytosolic fraction and of initiation factor eIF-2 for changes of the rate of protein synthesis during liver regeneration

The protein synthesis-stimulating activity of the cytosolic fraction from regenerating rat liver was tested in a cell-free system using washed polysomes from normal rat liver. This activity undergoes significant changes during liver regeneration after partial hepatectomy (p.h.). An initial decrease until 16 h after p.h. is followed by a significant increase until 24 h after p.h. Beyond 32 h after p.h. the activity begins to decline again. Evidence is presented that these changes of the cytosolic activity may not be due to alterations in the distribution of protein synthesis-stimulating factors between the microsomal and the cytosolic fraction. The Met-tRNAf-binding activity of the cytosolic fraction changes during liver regeneration analogously to the protein synthesis-stimulating activity measured in the polysomal assay. This indicates that initiation factor eIF-2 is involved in the observed changes of the cytosolic activity. This conclusion could be confirmed by addition of purified eIF-2 to the polysomal assay system. Addition of eIF-2 to cytosolic fractions of low endogenous protein synthesis-stimulating activity (16 h after p.h.) enhances amino-acid incorporation to a significantly higher extent than addition to highly active cytosolic fractions (24 h and 32 h after p.h.). From these results it is concluded that changes in eIF-2 plays an essential role in the described alterations of the cytosolic activities during liver regeneration.     

The infectivity and purification of cultured Plasmodium berghei ookinetes

Plasmodium berghei ookinetes were cultured from hamster blood as described previously (Kurtti and Munderloh, 1986). An average of 7.3 X 10(6) ookinetes was harvested from each ml of blood. Ookinetes were purified by centrifugation on first a 40% and then a 36% Percoll gradient. The final preparation comprised 32.8% of the ookinetes initially obtained, and contained 3.3 other parasite stages or blood cells per ookinete. Unpurified and purified ookinetes were resuspended in hamster blood and fed to Anopheles stephensi. There was a strong linear correlation between the concentration of purified or unpurified ookinetes and the number of oocysts formed. With unpurified ookinetes, a maximum was reached when preparations containing 1 X 10(7) ookinetes/ml were fed, and feeding preparations containing a higher concentration did not produce more oocysts. Sporozoites were found in the salivary glands of mosquitoes fed ookinetes by days 14 (unpurified) or 15 (purified) PI. Approximately 5 times as many purified as unpurified ookinetes were required to produce each oocyst.     

The effect of repeated administration of insulin on pain threshold and gamma-aminobutyric acid level in mouse brain

In experiments on male Albino-Swiss mice weighing 18-22 g insulin given in doses of 2 i.u./kg caused no change in the time of reaction to pain, while the same dose administered daily for 7 days potentiated the analgesic action of morphine (3 mg/kg s.c.). Glucose caused no change in this effect of insulin. After 14 days of insulin treatment the time of reaction to pain in the animals subjected to the action of morphine returned to its initial value. Twenty-four hours after the last administration of morphine the level of gamma-aminobutyric acid (GABA) was found to be decreased in the animals receiving insulin with glucose. These results suggest that the central action of insulin is dependent not only on hypoglycaemia produced by it, but may be due also to its direct action on the central structures and an indirect action mediated by its effect on other neurotransmitter systems.     

Subcellular location of enzymes involved in the N-glycosylation and processing of asparagine-linked oligosaccharides in Saccharomyces cerevisiae

A particulate translation system isolated from the yeast Saccharomyces cerevisiae was shown to translate faithfully in-vitro-transcribed mRNA coding for a mating hormone precursor (prepro-alpha-factor mRNA) and to N-glycosylate the primary translation product after its translocation into the lumen of the microsomal vesicles. Glycosylation of its three potential sugar attachment sites was found to be competitively inhibited by acceptor peptides containing the consensus sequence Asn-Xaa-Thr, supporting the view that the glycan chains are N-glycosidically attached to the prepro-alpha-factor polypeptide. The accumulation in the presence of acceptor peptides of a membrane-specific, unglycosylated translation product (pp-alpha-F0) differing in molecular mass from a cytosolically located, protease-K-sensitive alpha-factor polypeptide (pp-alpha-Fcyt) by about 1.3 kDa, suggests that, in contrast to previous reports, a signal sequence is cleaved from the mating hormone precursor on/after translocation. This conclusion is supported by the observation that the multiply glycosylated alpha-factor precursor is cleaved by endoglucosaminidase H to a product with a molecular mass smaller than the primary translation product pp-alpha-Fcyt but larger than the membrane-specific pp-alpha-F0. Translation and glycosylation experiments carried out in the presence of various glycosidase inhibitors (e.g. 1-deoxynojirimycin, N-methyl-1-deoxynojirimyin and 1-deoxymannojirimycin) indicate that the N-linked oligosaccharide chains of the glycosylated prepro-alpha-factor species are extensively processed under the in vitro conditions of translation. From the specificity of the glycosidase inhibitors applied and the differences in the molecular mass of the glycosylated translation products generated in their presence, we conclude that the glycosylation-competent microsomes contain trimming enzymes, most likely glucosidase I, glucosidase II and a trimming mannosidase, which process the prepro-alpha-factor glycans down to the (Man)8(GlcNAc)2 stage. Furthermore, several arguments strongly suggest that these three enzymes, which apparently represent the full array of trimming activities in yeast, are exclusively located in the lumen of microsomal vesicles derived from endoplasmic reticulum membranes.     

Macromolecules in the receptor lymph of campaniform sensilla

Summary The receptor lymph of campaniform sensilla on the halteres of the blowfly, Calliphora vicina, was analyzed histochemically. Acid mucopolysaccharides were demonstrated by a test for iron-binding capacity (Hale-reaction). Further characterization by enzyme treatment showed that the receptor lymph contains hyaluronic acid and/or chondroitin sulfate. Ultrahistochemical studies gave evidence for glycoproteins in the inner and outer receptor lymph space. The significance of acid mucopolysaccharides for arthropod sensilla is discussed.     

Activity of long chain acyl-CoA synthetase in isolated alveolar type II cells

Fatty-acyl-CoA synthetase activity was determined in rat alveolar type II cells. Compared to whole-lung homogenate, the enzyme specific activity with palmitic acid was 3.6-fold higher in isolated type II alveolar cells. The enzyme in rat alveolar type II cells did not discriminate among various fatty acids, suggesting that supply of fatty acids rather than specificity might be an important factor for their activation in these cells.     

Glutamic acid-dihydrogen phosphate hydrogen-bonded networks: their proton polarizability as a function of cations present. Infrared investigations.

Glutamic acid [(L-glu)n] + dihydrogen phosphate systems are studied by infrared (IR) spectroscopy dried and hydrated at 75% relative humidity, as a function of both the phosphate-glutamic acid residue (Pi/glu) ratio and the type of cations present. It is shown that the glutamic acid groups form hydrogen-bonded chains with the phosphates. In these chains the positive charge fluctuates, and they show very large proton polarizability which increases in the series Li+,Na+,K+ systems. These chains are cross-linked via phosphate-phosphate hydrogen bonds, in which the proton is almost localized at one Pi. The comparison of the (L-glu)n + dihydrogen phosphate systems with the results obtained earlier in the case of (L-glu)n + hydrogen phosphate systems shows that the behavior of (L-glu)n + Pi systems strongly depends on the pH. Only with decreasing pH the conducting chains are formed. Finally, a hypothesis is discussed with regard to the charge conduction in the F0 subunit of the H+-ATPase in mitochondria.