Lipoxygenase from cucumber fruit: Localization and properties

The subcellular localization of lipoxygenase (LOX) from cucumber fruit has been studied. Two methods have been employed to obtain organelles; (1) maceration of the tissue, followed by separation on a linear sucrose gradient and (2) release from protoplasts by osmotic shock, followed by a discontinuous Ficoll gradient. It was possible to obtain high LOX activity in the intact protoplasts from both peel and flesh tissue. However, fewer intact vacuoles were obtained following osmotic rupture than from macerated tissue. Both methods produced more particulate LOX activity from the peel than from flesh tissue, and both showed that this activity was associated with the vacuoles. The cucumber LOX enzyme was similar to the potato and tomato enzymes, both in pH characteristics and substrate specificity.     

The antimutagenic effect of selenium on 7,12-dimethylbenz(a)anthracene and metabolites in the amesSalmonella/microsome system

The antimutagenic effect of selenium as sodium selenite, sodium selenate, selenium dioxide, and seleno-methionine was studied in the AmesSalmonella/microsome mutagenicity test using 7,12-dimethylbenz(a)anthracene (DMBA) and some of its metabolites. Selenium (20 ppm) as sodium selenite reduced the number of histidine revertants on plates containing up to 100 μg DMBA/plate. Increasing concentrations of selenium as sodium selenite, sodium selenate, and selenium dioxide up to 40 ppm Se progressively decreased the number of revertants caused by 50 μg DMBA. DMBA and its metabolites 7-hydroxymethyl-12-methylbenz(a)anthracene, 12-hydroxymethyl-7-methylbenz(a)anthracene, and 3-hydroxy-7,12-dimethylbenz(a)anthracene were mutagenic forSalmonella typhimurium TA100 in the presence of an S-9 mixture. Selenium supplementation as Na₂SeO₃ reduced the number of revertants induced by these metabolites to background levels. The antimutagenic effect of inorganic selenium compounds cannot be explained by toxicity of selenium as determined by viability tests withSalmonella typhimurium TA100. Selenium supplementation in all forms examined, except sodium selenate, decreased the rate of spontaneous reversion. Selenium as sodium selenate was slightly mutagenic at concentrations of 4 ppm or less. Higher concentration of Na₂SeO₄ inhibited the mutagenicity of DMBA. The present studies support the anticarcinogenic potential of selenium and indicate that form and concentration are important factors in this trace element's efficacy.     

Cell patterning in branched and unbranched fruiting bodies of the cellular slime mold Polysphondylium pallidum

Cell patterning, the percentage of spores and stalk cells, was measured in branched and unbranched asexual fruiting bodies of Polysphondylium pallidum. Unlike D. discoideum, where small and large fruiting bodies are more stalky than average-sized fruiting bodies, the overall cell patterning was the same in branched and unbranched fruiting bodies of all sizes in P. pallidum. Light greatly increased the numbers of fruiting bodies in P. pallidum per unit area (or decreased aggregation territory size) so that most fruiting bodies formed in the light were small and unbranched. By contrast, light had little effect on the cell patterning of P. pallidum, although there was a slight increase in the percentage of stalk cells in the light compared to the dark. This indicates that the mechanisms governing light sensitivity of aggregation territory size and cell patterning have different components in P. pallidum. The accuracy of cell patterning of individual branches of branched fruiting bodies was so imprecise as to leave doubt that patterning is occurring at the branch level. Individual whorls of branched fruiting bodies had a greater percentage spores (90%) than whole fruiting bodies (78%) and the cell patterning was relatively imprecise. Only in whole fruiting bodies was the spore:stalk ratio highly correlated. These findings are consistent with cell pattern determination operating at the whole aggregate level, rather than at the individual whorl or branch level in P. pallidum.     

Kinetics of ionic transport across frog skin: Two concentration-dependent processes

Summary Sodium and chloride influxes across the nonshort-circuited isolated skin ofRana esculenta were measured at widely varying external ionic concentrations.The curve describing sodium transport has two Michaelis-Menten components linked at an inflection point occurring at an external sodium concentration of about 7 meq. Chloride transport can also be represented by two saturating components. A possible explanation of these kinetics is discussed.At sodium concentrations lower than 4 meq it is possible to define a component of the sodium transport mechanism as having a high affinity for sodium and which is independent of the nature of the external anion. A high affinity for chloride of the chloride transport system functioning at low external concentrations is also found but is significantly different from that of sodium. These systems show the physiological characteristics of the countertransports (Na _ext ⁺ /H _int ⁺ ; Cl _ext ^– /HCO _3int ^– ) functioning at low external concentrations.At external concentrations higher than 4 meq a low affinity transporting system in which chloride and sodium are linked superimpose on the high affinity components.The physiological significance of these results is discussed.     

Ca2+ regulated modulator protein interacting agents: inhibition of Ca2+-Mg2+-ATPase of human erythrocyte ghost.

Agents such as N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), and its derivatives, chlorpromazine and amitriptyline that interact with calcium-regulated modulator protein were found to inhibit not only Ca²⁺ dependent cyclic nucleotide phosphodiesterase but also Ca²⁺-Mg²⁺-ATPase of human erythrocyte ghosts. I₅₀ values of modulator interacting agents for testis modulator-activated, brain modulator-activated and erythrocyte modulator-activated-ATPase are indistinguishable. However, I₅₀ of W-7 for troponin C-activated-ATPase is lower than that for modulator-activated ATPase. The specificity of these agents toward modulator-related enzyme reaction is also shown by the negative effect on modulator-unrelated enzyme system such as erythrocyte ghost protein kinase and Mg²⁺-ATPase. These agents provide a useful tool for elucidating the physiological role of modulator.     

Role in hemolysis of the interaction of tellurium compounds with glutathione

We have shown that tellurite and tellurate require the interaction with reduced glutathione (GSH) to hemolyze human erythrocytes. The study of the nature of this interaction is the main object of this paper. The degree of hemolysis was determined by the method of Angelone. The addition of extracellular 1 mM GSH or cysteine increased the rate of hemolysis. Concanavalin A (0.3 mg/mL) and/or 4 mg/mL adenosine did not affect the hemolysis by 0.1 mM tellurite. One tenth to 1 mM 4-acetamido-4′-isothiocyanostilbene-2,2′-disulfonate (SITS) inhibited this hemolysis by 60–100%. Millimolar GSH released this inhibition. Incubation of 0.1 mM tellurite with 1 mM GSH for 90 min at 37°C, produced a hemolytic agent when prepared and tested under nitrogen, but one that was not active when prepared in air. The hemolysis byp-hydroxymercuribenzoate orp-hydroxymercuriphenylsulfonate did not involve GSH. Scanning electron micrographs showed a sphero-echinocyte transformation, in the pre-hemolytic stage, with all the agents tested. The rate of penetration of tellurite plays a role in determining the rate of hemolysis, as shown by the effect of SITS. The release by GSH of the inhibition by SITS poses questions concerning the site of action and cell membrane penetration of the hemolytic agent. Telluride or some intermediate in the interaction of GSH with tellurite is the actual hemolytic agent.     

The genusPicris (Asteraceae,Lactuceae) in Tropical Africa

Three species of the genusPicris L. are native in Tropical Africa:P. abyssinica Sch. Bip. (Ethiopia),P. xylopoda Lack, spec. nova (Nigeria, Ethiopia) andP. humilis DC. (Senegal, Mali). There are indications that the two perennial species,P. abyssinica andP. xylopoda, are related to and have evolved from a primitive Central Asiatic stock in a manner parallel to many African species ofCrepis L.P. humilis, on the other hand, is a small annual plant with a high number of derived characters. The introduced species of European origin growing south of the Sahara are briefly mentioned.     

Synthesis and degradation of proteins during wheat endosperm development

Synthesis of proteins rich in lysine declines progressively with endosperm development and these proteins appear to be degraded preferentially at later stages. The proteolytic enzymes in extracts of endosperms at a late stage of development release considerably more lysine radioactivity from labelled endosperm proteins as compared with the enzymes in endosperms at an early stage.     

The first optic ganglion of the bee

Summary The arrangement of first and second order neurons in an optic cartridge and the topographical relationships of the second order neurons within a cartridge and to groups of surrounding cartridges have been analyzed in the visual system of the bee, Apis mellifera, from light and electron microscope studies on Golgi preparations. At the level of the monopolar cell body layer, the nine retinula cell fibres of each ommatidium, the six short visual fibres arranged in a circle surrounding the three long visual fibres, become cartridges as a consequence of the appearance of the second order neurons (L-fibres) which join the R-fibre bundles. Two of the four different L-fibre types, L-1 and L-2, remain together in the centre of the cartridge throughout the lamina. The axons of the L-3 and L-4 fibres, however, have their position integrated into the circle formed by the endings of the short visual fibres. On the basis of further examination of light and especially electron microscopical Golgi material, the different L-fibres can be classified into four types which appear in each cartridge. The clear stratification in the first synaptic region (A, B and C) seems to be the best criterion for a morphological classification since such a classification necessarily also includes a functional basis. According to a naming system based on the position of the lateral processes, L-fibres with side branches in strata A, B and C are called L-1 fibres. Fibres with lateral processes in strata A and B are L-2 fibres; monopolar cell fibres with branches only in the second stratum B are L-fibres of type 3; and all monopolar cells with branches only in stratum C are called L-4 fibres. In addition to the branching pattern covering only the parent cartridge, two of the four fibre types (L-2 and L-4) have long collaterals reaching neighbouring cartridges: L-2 in stratum A and L-4 in stratum C. These collaterals presumably form a substrate for lateral interactions.     

The cryopreservation of mouse leukemic cells. I. Effects on drug resistance and the patterns of nucleic acid metabolism.

Cultured L1210 lymphocytic leukemic cells resistant to cytosine arabinoside or Cytoxan were frozen under different conditions for up to 5 months and transplanted into recipient mice. Biochemical determinations including DNA, total RNA and drug resistance suggested that the more rapid, less expensive method of freezing mouse leukemic cells enables good retention of each parameter. Examination of cellular and subcellular RNA fingerprints indicated several alterations in the localizations f certain subspecies of RNA. Nonetheless, all cells retained their overall viability and the capacity to induce leukemia in CDF₁ mice.