Plankton development in a rapidly flushed lake in the River Spree system (Neuendorfer See, Northeast Germany)

The Neuendorfer See is a shallow lake through which the RiverSpree flows. In the lake, abundances of zooplankton (mainlyrotifers) and phytoplankton increased exponentially over theflowing stretch between the inflow and the outflow of the river.Increase in space is enhanced by increased residence time inthe lake. Sensitivity of plankton development on residence timesof >8 days weakened at longer residence times. This patternholds for all zooplankton species. Rates of change in chlorophylland rotifers (after correction for temperature) are first enhanced,then are decreased at longer residence times. Concentrationsof dissolved inorganic nutrients [Si, soluble reactive phosphorus(SRP) and NO₃–] and the N/P ratio diminished with increasingresidence time. The plankton dynamics in the lake were dependenton discharge and the lake behaved as a ‘plug flow tubularreactor’ with minor longitudinal mixing. This was notdifferent from the transportation in large rivers.     

Effects of steroid hormones and other substances on alarm substance cells and mucous cells in the epidermis of the European minnow, Phoxinus phoxinus (L.), and other Ostariophysi (Pisces)

The alarm substance cells and mucous cells of various species of Ostariophysi do not react uniformly to treatment with androgen and other steroid hormones. This indicates that the mechanism controlling formation of alarm substance is not uniform in the Ostariophysi and three exist at least two such mechanisms, one of which is operated by androgens and perhaps other steroid hormones of the gonads. Steroid hormones from the adrenal cortex proved ineffective. In the European minnow, anti-androgen (androcur®, cyproteroneacetate) had an efrect opposite to that of androgen, while androgen treatment upon this species led to an increase in the size of mucous cells and a reduction in the alarm substance cells. The epidermis of androgen-treated European minnows contained neither alarm substance cells nor alarm substance, and skin extracts of such fish proved ineffective in behaviour experiments upon fish schools. The effect of further hormone treatments are discussed and the reactions of the European minnow are compared to those of other species.     

HLA-DR is a procoagulant

Numerous incidents of thromboembolic complications have been documented in cancer patients and in recipients of mismatched organ transplants. Tumor procoagulants have also been implicated in the process of metastasis. Two protein bands of 35,000 and 28,000 daltons isolated from human ovarian carcinoma possessed procoagulant activity. The 35,000 dalton protein had an amino terminal sequence identical to that of the major histocompatibility antigen HLA-DR. Further, isolation of the protein using immunoaffinity column chromatography with monoclonal antibody to HLA-DR resulted in the isolation of procoagulant activity. The immunoaffinity purified protein enhanced thrombin generation in recalcified normal plasma approximately 20- fold. HLA-DR procoagulant activity was completely inhibited by Staphylococcal enterotoxin A. We propose that the procoagulant nature of HLA-DR may contribute to thrombotic disorders in several cancers and in association with graft rejection. The ability of enterotoxin A to inhibit this procoagulant may lead to development of future therapeutic strategies.     

Tyrosine phosphorylation of Munc18‐1 inhibits synaptic transmission by preventing SNARE assembly

Tyrosine kinases are important regulators of synaptic strength. Here, we describe a key component of the synaptic vesicle release machinery, Munc18‐1, as a phosphorylation target for neuronal Src family kinases (SFKs). Phosphomimetic Y473D mutation of a SFK phosphorylation site previously identified by brain phospho‐proteomics abolished the stimulatory effect of Munc18‐1 on SNARE complex formation (“SNARE‐templating”) and membrane fusion in vitro. Furthermore, priming but not docking of synaptic vesicles was disrupted in hippocampal munc18‐1‐null neurons expressing Munc18‐1_Y473D. Synaptic transmission was temporarily restored by high‐frequency stimulation, as well as by a Munc18‐1 mutation that results in helix 12 extension, a critical conformational step in vesicle priming. On the other hand, expression of non‐phosphorylatable Munc18‐1 supported normal synaptic transmission. We propose that SFK‐dependent Munc18‐1 phosphorylation may constitute a potent, previously unknown mechanism to shut down synaptic transmission, via direct occlusion of a Synaptobrevin/VAMP2 binding groove and subsequent hindrance of conformational changes in domain 3a responsible for vesicle priming. This would strongly interfere with the essential post‐docking SNARE‐templating role of Munc18‐1, resulting in a largely abolished pool of releasable synaptic vesicles.     

The degree of stacking and the average membrane area of thylakoids in lettuce chloroplasts

The surface density of stacked and total thylakoid membranes in chloroplasts was determined morphometrically using the method of vertical sections. The degree of stacking, defined as the fraction of the total membrane area which is involved in stacking, was calculated from the surface densities and found to be 0.70 for chloroplasts of lettuce grown under field conditions. An average membrane area of 500 microns 2 for the thylakoids in a chloroplast was obtained from the surface density and the average volume of the chloroplasts (11.6 microns 3, estimated by means of equivalent oblate spheroids). The advantage of the morphometric method over alternative techniques and the relevance of the results with respect to the topology of thylakoid membranes are discussed.     

Changes of cell surface configuration and regulation of cell proliferation

The electric surface charge configuration of 3T3 and SV40-3T3 cells was characterized by determining the product of electrophoretic mobility of the cells times the viscosity of suspension medium. This quantity could be shown to change with temperature and/or treatment with calf serum or trypsin in close correlation with the effects of these agents on characteristics of cell proliferation. The present results, taken together with those of earlier studies on cell-electrophoresis and characterization of lipid constituents of the cells, support the hypothesis of a lateral phase separation in the plasmamembrane as triggering process in stimulation of proliferation of resting normal cells.     

The interaction of ribonuclease T 1 with DNA.

The interaction of RNase T1 with calf thymus DNA was studied using uv difference spectroscopy and the effect of the enzyme on DNA melting. There was no indication of RNase T1 binding with native DNA. A prominent difference spectrum for RNase T1 binding with denatured DNA (d-DNA) was observed at pH 5, 25 degrees and low ionic strength (mu = .01 M) which was depressed at higher ionic strength and pH. The normalized difference spectrum at mu = .01 M, pH 5 and 25 degrees can be interpreted as indicating an interaction of an exposed guanine residue directly with the enzyme and a coupling of this process with the "melting" of short folded segments of d-DNA. The apparent association constant calculated per M guanine residues was 2.4 X 10-4 M-1 under these conditions. The results are discussed in reference to comparable studies on the interaction of RNase T1 with RNA and small guanine ligands.     

Isolation and identification of a 23,000-dalton heparin binding fragment from the amino terminus of bovine thrombospondin

Bovine freeze-thaw lysed platelets were fractionated by dextran sulfate affinity chromatography and a purified protein of 23,000 Da was subsequently obtained by G-75 gel filtration of the 0.5 M NaCl fraction. This protein had an amino terminal sequence of Asn-Arg-Ile-Pro-Glu-Ser-Gly-Gly-Asp-Asn-Ser-Val-Phe-Asp-Ile-Phe-Glu-Leu- Thr-Gly-Ala-Ala-Trp-Lys-, a sequence identical to that reported for human thrombospondin. Thrombin-released platelets, fractionated in an identical manner, yielded a protein of 30,000 Da. Immunoblotting of purified bovine platelet thrombospondin and the 150,000- and 30,000-Da plasmin-generated thrombospondin fragments indicated that polyclonal antisera raised against the 23,000-Da protein cross-reacted with intact thrombospondin and the 30,000-Da fragment but not the 150,000-Da fragment. The 23,000-Da protein possessed weak heparin neutralization activity.