Kinetics of leaf nitrite reductase with Methyl Viologen and ferredoxin under controlled redox conditions.

The dexamethasone binding capacity of embryonal carcinoma cells and their differentiated derivatives was investigated. Manipulation of the embryonal carcinoma cell-culture conditions resulted in an unstable reversible expression of the glucocorticoid receptors. Stable expression of the receptors is observed when these cells are induced to differentiate. Cells grown under identical conditions were assayed for their ability to bind epidermal growth factor.     

Isodityrosine, a new cross-linking amino acid from plant cell-wall glycoprotein.

1. Cell-wall hydrolysates from calli of all higher plants tested contained a new phenolic amino acid for which the trivial name isodityrosine is proposed. Isodityrosine was shown to be an oxidatively coupled dimer of tyrosine with the two tyrosine units linked by a diphenyl ether bridge. 2. The amount of isodityrosine in sodium dodecyl sulphate-insoluble cell-wall preparations was proportional to the amount of hydroxyproline. 3. Acidified chlorite split the diphenyl ether bridge of isodityrosine, and concomitantly solubilized the cell-wall glycoprotein. 4. Dithiothreitol inhibited isodityrosine synthesis in vivo, and suppressed in parallel the covalent binding of newly synthesized protein in the cell wall. 5. It is suggested that isodityrosine is an inter-polypeptide cross-link responsible for the insolubility of plant cell-wall glycoprotein.     

EPR spectra of photosystem I and other iron protein components in intact cells of cyanobacteria.

Electron paramagnetic resonance (EPR) spectra were recorded of whole filaments of the cyanobacteria Nostoc muscorum and Anabaena cylindrica. Signals due to manganese were removed by freezing and thawing the cells in EDTA. EPR spectra were assigned on the basis of their g values, linewidths, temperature dependence and response to dithionite and light treatments. The principal components identified were: (i) rhombic Fe3+ (signal at g = 4.3), probably a soluble storage form of iron; (ii) iron-sulfur centers A and B of Photosystem I; (iii) the photochemical electron acceptor 'X' of Photosystem I; this component was also observed for the first time in isolated heterocysts; (iv) soluble ferredoxin which was present at a concentration of 1 molecule per 140 +/- 20 chlorophyll molecules; (v) a membrane-bound iron-sulfur protein (g = 1.92). A signal g = 6 in the oxidized state was probably due to an unidentified heme compound. During deprivation of iron the rhombic Fe3+, centers A, B and X of Photosystem I, and soluble ferredoxin were all observed to decrease.     

Cell adhesion and acquisition of detergent resistance by the cytoskeleton of cultured chick fibroblasts

About 30% of the proteins of adherent cultured chick embryo fibroblasts are not solubilized by the non-ionic detergent Triton X-100 and remain firmly attached to the substratum. The insoluble residue contains a considerable part of the cell's cytoskeleton and its major constituents are large external transformation-sensitive (LETS) protein, the heavy chain of myosin, a 52,000 molecular weight protein and actin. Kinetic studies reveal that cytoskeleton insolubility in Triton is acquired either concurrently with cell adhesion or very closely with it. Neither cell adhesion nor binding of the Triton cytoskeleton to the substratum require de novo synthesis of protein. In the attempt to assess the role of LETS protein in cytoskeleton attachment, we find that trypsin-detached cells rapidly acquire Triton-insoluble cytoskeleton although their LETS protein content is about 15--20% of its level in long-term cultures. Removal of the great majority of LETS molecules of adherent cultures by either urea or trypsin treatment does not affect the relative amount or composition of the anchored cytoskeletal proteins. Also, LETS protein of cultures exposed to cycloheximide for extended periods of time, is reduced to 10% of its maximum amount without much affecting the attachment and composition of the cytoskeleton. It is deduced that the great majority of LETS protein is not required for the attachment of the Triton cytoskeleton to the substratum.     

Rapid separation of low molecular weight solutes from liposomes without dilution

Liposomes can be separated from low molecular weight solutes on minicolumns of Sephadex G-50 made from the barrels of 1- or 5-ml plastic syringes. Excess fluid is first removed from the Sephadex beads by centrifugation and a mixture of liposomal entrapped and free solute is applied to the column bed. The centrifugation is repeated forcing the liposomal material through the column into a test tube while the free solute is quantitatively retained in the Sephadex. The procedure is applicable to a variety of solutes and 92 to 100% recovery is achieved for both charged and neutral liposomes. This technique has advantages over other methods for separating extraliposomal solutes from liposomes. Numerous samples can be processed simultaneously within minutes with no dilution of the liposomal preparation. Nonentrapped solute within the Sephadex can be easily recovered in a small volume of water or buffer.     

Distribution of Bdellovibrio bacteriovorus in sewage works, river water, and sediments.

Bdellovibrio was found in all liquid phases of the sewage works examined. The predator was also found in all the river sediments and sewage-polluted river waters examined but could not be found in some unpolluted river waters. Bdellovibrio was able to multiply on the high numbers of bacteria present in the aerobic percolating filter film but could not survive in anaerobic sludge. Similarly, the predator was present in the aerobic surface layers of river sediments but not in the anaerobic bottom layers. The major source of Bdellovibrio in the polluted rivers examined were sewage works effluents, and numbers in both river water and sediment were correlated with river water quality. It was unlikely that Bdellovibrio was important in reducing numbers of other bacteria in either sewage or river sediment.     

Flow cytometry of the differentiation of Physarum polycephalum myxamoebae to cysts

Myxamoebae of Physarum polycephalum, strain Cld, were grown on agar lawns on live bacteria. Myxamoebae were harvested, fixed and stained with propidium iodide. Flow cytometry showed that, as in the case of Physarum plasmodia, there is no G1 phase during rapid exponential growth. However, an apparent G1 phase was observed at the end of exponential growth when the culture arrested with the G1 DNA content for about a day between growth and differentiation. Most myxamoebae differentiated into cysts, but some formed microplasmodia and others appeared to lose DNA. The cysts possessed the G2 phase DNA content and there was an S phase connecting the G1-arrested state with the encysted state. Encystment was blocked by hydroxyurea (HU) suggesting that DNA synthesis is essential for encystment. The natural temporary synchronization in G1 phase may provide the basis of a method for selecting mutants with a conditional block in G2 or M phases.