Reciprocal changes in fructose-6-phosphate,2-kinase and fructose-2,6-bisphosphatase activity in response to glucagon and epinephrine

The effect of hormones on the enzymes responsible for the synthesis (fructose-6-P,2-kinase) and degradation (fructose-2,6-Pase) of fructose-2,6-P₂ was examined in isolated rat hepatocytes. Glucagon (10^?11 M), epinephrine (10^?5 M), or calcium (2.4 mM) and A23187 (10^?5 M) administration to hepatocytes produced simultaneous activation of fructose-2,6-Pase and inactivation of fructose-6-P,2-kinase within 2 minutes. The effect of epinephrine on these two enzymes was dependent on the presence of Ca⁺⁺. These results suggest that the level of fructose-2,6-P₂ is controlled by recriprocal changes in fructose-2,6-Pase and fructose-6-P,2-kinase activities.     

Two Dictyostelium tyrosine kinase–like kinases function in parallel,stress-induced STAT activation pathways

When Dictyostelium cells are hyperosmotically stressed, STATc is activated by tyrosine phosphorylation. Unusually, activation is regulated by serine phosphorylation and consequent inhibition of a tyrosine phosphatase: PTP3. The identity of the cognate tyrosine kinase is unknown, and we show that two tyrosine kinase–like (TKL) enzymes, Pyk2 and Pyk3, share this function; thus, for stress-induced STATc activation, single null mutants are only marginally impaired, but the double mutant is nonactivatable. When cells are stressed, Pyk2 and Pyk3 undergo increased autocatalytic tyrosine phosphorylation. The site(s) that are generated bind the SH2 domain of STATc, and then STATc becomes the target of further kinase action. The signaling pathways that activate Pyk2 and Pyk3 are only partially overlapping, and there may be a structural basis for this difference because Pyk3 contains both a TKL domain and a pseudokinase domain. The latter functions, like the JH2 domain of metazoan JAKs, as a negative regulator of the kinase domain. The fact that two differently regulated kinases catalyze the same phosphorylation event may facilitate specific targeting because under stress, Pyk3 and Pyk2 accumulate in different parts of the cell; Pyk3 moves from the cytosol to the cortex, whereas Pyk2 accumulates in cytosolic granules that colocalize with PTP3.     

Trypanosoma gambiense: immunosuppression and polyclonal B-cell activation in mice

The relationship between the suppression of antibody response and polyclonal B-cell activation was studied in mice treated with a cell homogenate of Trypanosoma gambiense. The cell homogenate injection in mice caused a progressive increase in splenic background plaque-forming cell response to sheep erythrocyte. In the mice with markedly increased background plaque-forming cell response, the different reactivity in the primary antibody response to sheep erythrocytes was observed between the intraperitoneal and intravenous immunization with sheep erythrocytes. The intraperitoneal immunization of mice with sheep erythrocytes strongly suppressed the antibody response, while the intravenous immunization with sheep erythrocytes led to an enhancement of the antibody response. The intraperitoneal injection of silica particles, a toxic agent to macrophages, 30 min before intraperitoneal immunization with sheep erythrocytes abolished the suppression of the antibody response completely. In addition, restoration of the suppressed antibody response was found in mice immunized intraperitoneally with a high dose of sheep erythrocytes. It appears that the suppression of antibody response is not attributable to polyclonal B-cell activation, and is associated with the elevation of the phagocytic activity of peritoneal macrophages.     

Characterization of a filamentous biofilm community established in a cellulose-fed microbial fuel cell

Background  

Microbial fuel cells (MFCs) are devices that exploit microorganisms to generate electric power from organic matter. Despite the development of efficient MFC reactors, the microbiology of electricity generation remains to be sufficiently understood.     

Morphological behavior of cultured bovine adrenal medulla capillary endothelial cells.

Bovine adrenal medulla capillary endothelial cells were isolated and cloned, and their morphological behaviors in vitro were examined. In the culture of primary or early passage, one type of colony formed intracellular lumina both on the dish and in the three dimensional collagen gel. Another type proliferated well and showed morphology ranging from slender-shape to cobblestone shape, and were easily cloned. Cloned cells which showed slender-shapes formed tubular network on plastic dish after addition of PMA, OAG or vanadate, and these cells also formed multicellular tubules in the three dimensional collagen gel. However, the formation of diaphragmed fenestrae by these slender-shape clones was rare. One clone which showed cobblestone shape formed diaphragmed fenestrae, when cultured on collagen gel for more than one month. Isolated colonies or clones showed heterogeneity of cell shape, angiogenic behaviors and fenestrae formation.     

Partial Characterization of Phytochrome I and II in Etiolated and De-Etiolated Tissues of a Photomorphogenetic Mutant (lh) of Cucumber (Cucumis sativus L.) and Its Isogenic Wild Type

A photomorphogenetic mutant (lh) of cucumber has been suggestedto lack light-stable phytochrome function [Adamse et al. (1987)J. Plant Physiol. 127: 481-491]. The present work reports biochemicaland immunochemical characteristics of phytochrome in this cucumbermutant. Spectrophotometric measurement of phytochrome extractedfrom the etiolated seedlings indicated that the mutant containeda similar amount of phytochrome to that of the wild type. Nosignificant differences in apparent molecular mass and reactivityagainst an anti-pea phytochrome monoclonal antibody were observed.Phytochrome in de-etiolated seedlings was partially purifiedto enable spectrophotometric measurement. The phytochrome contentand difference spectrum for photoconversion was very similarin extracts of the mutant and the wild type. Furthermore, thephytochrome extracted from de-etiolated tissues of the mutantand the wild type appear to contain similar amounts of phytochromeI and II, since in both about one quarter of the phytochromein the fraction could be immunoprecipitated by an antibody whichrecognizes phytochrome I. Two possibilities to explain the Ilphenotype are: (i), the mutation changes the function of phytochromeI and/or II without changing its stability and spectrophotometricalcharacteristics; (ii), the mutation results in modificationof transduction chains between the photo-receptor and physiologicalresponses. (Received February 1, 1989; Accepted April 14, 1989)