An SS1-SS2 {beta}-barrel structure for the voltage-activated potassium channel

To examine the feasibility of a ß structure for thepore-lining region of the voltage-gated potassium channel, wehave characterized a family of 12 antiparallel ß-barrels.Each is comprised of four identical pairs of ß-strandsorganized with approximate 4-fold symmetry about a channel axis.The Cand N-termini of the ß-strand pairs are assumedto be at the extracellular end of the channel, and each pairis connected by a hairpin turn at the intracellular end of thechannel. The models differ in the residues located in the hairpinturn and in the orientation of the two strands of each pairin the barrel, i.e. whether the C-terminus of a pair is clockwise(CW) or counterclockwise (CCW) from the N-terminus when thechannel is viewed from outside the cell. Following known structureprecedents and potential energy predictions, the barrel is assumedto be right-twisting in all cases. All models have crowded layersof inward-projecting aromatic sidechains near the center ofthe channel which could regulate channel selectivity. The modelswith an odd number of amino acids in the hairpin turn have theadvantage of predicting that F433 points into the barrel, butthe disadvantage that V438 does not. Of these models, two ofthe models are most consistent with the external tetraethylanunonhim(TEA) block data, and of those, one (T439 CCW 3:5) is most consistentwith the internal TEA block data.     

Calcium Ions Regulate K+ Uptake into Brain Mitochondria: The Evidence for a Novel Potassium Channel

The mitochondrial response to changes of cytosolic calcium concentration has a strong impact on neuronal cell metabolism and viability. We observed that Ca²⁺ additions to isolated rat brain mitochondria induced in potassium ion containing media a mitochondrial membrane potential depolarization and an accompanying increase of mitochondrial respiration. These Ca²⁺ effects can be blocked by iberiotoxin and charybdotoxin, well known inhibitors of large conductance potassium channel (BK_Ca channel). Furthermore, NS1619 – a BK_Ca channel opener – induced potassium ion–specific effects on brain mitochondria similar to those induced by Ca²⁺. These findings suggest the presence of a calcium-activated, large conductance potassium channel (sensitive to charybdotoxin and NS1619), which was confirmed by reconstitution of the mitochondrial inner membrane into planar lipid bilayers. The conductance of the reconstituted channel was 265 pS under gradient (50/450 mM KCl) conditions. Its reversal potential was equal to 50 mV, which proved that the examined channel was cation-selective. We also observed immunoreactivity of anti-β₄ subunit (of the BK_Ca channel) antibodies with ~26 kDa proteins of rat brain mitochondria. Immunohistochemical analysis confirmed the predominant occurrence of β₄ subunit in neuronal mitochondria. We hypothesize that the mitochondrial BK_Ca channel represents a calcium sensor, which can contribute to neuronal signal transduction and survival.     

Glucose oxidase: A potential option to decrease the oxidative stress in stirred probiotic yogurt

The effect of the addition of glucose oxidase as a technological option todecrease the oxidative stress in a stirred yogurt during 15 days of refrigerated storage was investigated. A significant increase in the viable population of Bifidobacteria longum (6.9–8.7 log CFU g^?1) was observed in all yogurts added with glucose oxidase and glucose. Additionally, the yogurts containing glucose oxidase and glucose presented and caused higher pH, proteolysis rate, and contents of organic acids and aroma compounds, and this effect was comparable to the control sample (without glucose oxidase and glucose). Overall, the combined effect of the glucose oxidase system was important to reduce the oxygen content during storage of the probiotic yogurt. These findings suggest that glucose oxidase is a potential option to decrease the oxidative stress in probiotic yogurts.     

Hairy root nodulation of Casuarina glauca: a system for the study of symbiotic gene expression in an actinorhizal tree

The purpose of this study was to establish a fast system for producing transgenic actinorhizal root nodules of Casuarina glauca. Agrobacterium rhizogenes strain A4RS carrying the p35S-gusA-int gene construct was used to induce hairy roots on hypocotyls of 3-week-old C. glauca seedlings. Three weeks after wounding, the original root system was excised, and composite plants consisting of transgenic roots on untransformed shoots were transferred to test tubes to be inoculated with Frankia. The actinorhizal nodules formed on transformed roots had the nitrogenase activity and morphology of untransformed nodules. beta-Glucuronidase (GUS) activity was examined in transgenic roots and nodules by fluorometric and histochemical assays. The results indicate that transgenic nodules generated with this root transformation system could facilitate the molecular study of symbiotic nitrogen fixation in actinorhizal trees.     

Calciumβ″-alumina and Nasicon electrolytes in galvanic cells with solid reference electrodes for detection of sulphur oxides in gases

Calcium-β″-alumina and Nasicon were applied as solid electrolytes for SO _x (x=2 or 3) gas detection. The following two galvanic cells with solid reference electrodes were assembled $$\begin{gathered} Pt|O_2 ,CaO||Ca - \beta '' - Al_2 O_3 ||CaSO_4 |SO_3 ,SO_2 ,O_2 |Pt \hfill \\ Pt|O_2 ,Na_2 O||Nasicon||Na_2 SO_4 |SO_3 ,SO_2 ,O_2 |Pt \hfill \\ \end{gathered} $$ Calcium and sodium sulphates were used as auxiliary electrolytes to provide protection of β″-Al₂O₃ or Nasicon electrolytes from chemical reaction with SO₂. The e.m.f. was measured in the temperature range 850–1070 K for five various test gases. The measured e.m.f.s had values a little lower than the calculated ones. The results show clearly that both the cells can act as SO _x electrochemical sensors for temperatures not exceeding 1070 K.     

Estimation of children exposure to organochlorine compounds through milk in Rio Grande do Sul,Brazil

The presence of organochlorine pesticides (α-HCH, lindane, aldrin, HCB, pp′-DDE, op′-DDD, pp′-DDD, and op′–DDT) and PCBs (congeners 10, 28, 52, 138, and 180) were investigated in raw, pasteurized, and UHT milk from Rio Grande do Sul State (Brazil). Considering the toxicity of these compounds and the importance of milk and dairy products for child nutrition, the estimated daily intake (EDI) of these compounds, through milk, by elementary school children of Santa Maria (Rio Grande do Sul, Brazil) was also determined. HCB and pp′-DDE were found in all samples analyzed. pp′-DDE (11.9 ng/g), op′-DDD (7.38 ng/g), lindane (6.09 ng/g), and PCB 180 (5.31 ng/g) were the compounds found at the highest average concentrations. The EDIs for organochlorine pesticides were below the acceptable daily intakes established by FAO/WHO. Furthermore, few samples exceeded the maximum residue limits for the compounds evaluated.