Diferric transferrin reductase in the plasma membrane is inhibited by adriamycin

Diferric transferrin which is often necessary for growth of cells is reduced by the transplasma membrane electron transport system of HeLa cells with release of ferrous iron outside the cell. Reduction of external diferric transferrin is reflected in oxidation of internal NADH. Adriamycin, an antitumor drug, inhibits diferric transferrin reduction by the HeLa cells and inhibits concomittant oxidation of cytosolic NADH at concentrations, 10(-8)-10(-6)M, which inhibit cell growth. Isolated liver plasma membranes have an NADH diferric transferrin reductase activity which is inhibited by similar adriamycin concentrations. We propose that inhibition of cell growth by adriamycin can be based on inhibition of transplasmalemma diferric transferrin reductase.     

Extracellular ascorbate stabilization: Enzymatic or chemical process?

Ascorbate is stabilized in the presence of HL-60 cells. This stabilization has been questioned as a simple chemical effect. Further properties and controls about the enzymatic nature of this stabilization are described and discussed. Our results showed that cAMP derivatives and cAMP-increasing agents stimulated the ability of HL-60 cells to stabilize ascorbate. On the other hand, tunicamycin, a glycosylation-interfering agent, inhibited this ability. These data, together with hormonal regulation, support the hypothesis of an enzymatic redox system located at the plasma membrane as being responsible for the extracellular ascorbate stabilization by HL-60 cells.     

Calaminthadiol,a new 3,4-secotriterpenoid from Satureia calamintha and Satureia graeca

A new triterpenoid, calaminthadiol, 3,4-seco-4(23),12-ursadien-3,28-diol, was isolated from the leaves of Satureia calamintha and Satureia graeca. Its structure was elucidated by spectroscopic methods and partial synthesis. The natural occurrence of this compound can be conclusive for the chemotaxonomic characterization of the genus because of the rarity of the 3,4-fission in the α- and β-amyrin skeletons. A biogenetic mechanism for its formation is proposed. Sitosterol, stigmasterol and campesterol were also isolated.     

Polarization of plasma membrane glycoconjugates in amphibian epidermis during metamorphosis

Wheat germ agglutinin (WGA) binding sites have been examined in tadpole epidermal cells at the level of both light and electron microscopy using the WGA-ovomucoid-gold technique. In premetamorphic tadpoles the reaction was observed on the plasma membranes of epithelial cells showing a gradient from inner to outer membranes. These glycoconjugates were polarized during development, and at the end of metamorphic climax they were only located in plasma membranes of stratum corneum. The existence of an apical cell surface coat is needed to facilitate the absorption of water through the adult epidermis. The possible implications of this polarization process are discussed.     

Ecological constraints on the evolutionary association between field and preferred temperatures in Tropidurinae lizards

Ectothermic body temperatures affect organismal performances and presumably fitness, and are strongly influenced by the thermal environment. Therefore, the processes of colonization of novel thermal habitats by lizards might involve changes in thermal preferences, performance curves (reaction norms) and field activity temperatures. According to theory based on optimality analysis, diverse aspects of the thermal biology of vertebrate ectotherms should co-evolve as to maximize performance at the temperature range more often experienced by animals in the field. One corollary of this premise is that derived lizard clades that experienced a significant shift in thermal ecology, in comparison with the ancestral condition, should prefer and select temperatures in a thermal gradient similar to those experienced in nature. Here we report an analysis of the premise stated before. Specifically, we verify whether or not Tropidurinae species from three major Brazilian habitats (the Rainforests, the semi-arid Caatingas and the Cerrados, a Savannah-like biome) differ in thermal ecology and thermoregulatory behavior. The Caatinga is believed to be the ancestral habitat of this sub-family, and differences are expected because species from semi-arid habitats usually exhibit high body temperatures for lizards, whereas forest specialists might be thermoconformers and active at low temperatures. We also compared selected temperatures in the laboratory by species from the two open habitats (Caatingas and Cerrados). Data were analyzed using both conventional and phylogenetic analysis tools. Although species from Caatingas exhibited higher activity temperatures in nature than those from Cerrados, mean selected temperatures were similar between ecological groups. Phylogenetic analyses confirmed these findings and evidenced large␣evolutionary divergence in field activity temperatures between sister species from different␣open habitats without coupled divergence in selected temperatures. Therefore, thermoregulatory behavior and ecological parameters did not evolve similarly during the colonization of contrasting open habitats by Tropidurinae.