Phase transition kinetics of phosphatidic acid bilayers A stopped-flow study of the electrostatically induced transition

The kinetics of the electrostatically induced phase transition of dimyristoyl phosphatidic acid bilayers was followed using the stopped-flow technique. The phase transition was triggered by a fast change in the pH or the magnesium ion concentration and followed by recording the time dependence of the absorbance. When the phase transition was induced by a pH jump the time course of the absorbance could be described by two exponentials, their time constants displaying the for cooperative processes characteristic maximum at the transition midpoint. The time constants are in the 10 and 100 ms range for the H⁺ triggered transition from the fluid to the ordered state. A third slower process shows no appreciable temperature dependence and is probably caused by vesicle aggregation. For the OH^--induced transition fron the ordered to the fluid state the time constants are in the 100 and 1000 ms range. The fluid-ordered transition could also be triggered by addition of magnesium ions. Of the several observed processes only the fastest in the 10–100 ms time range could definitely be assigned to the fluid-ordered transition while the others are due to aggregation phenomena. The experimental data were compared with results obtained from pressure jump experiments and could be interpreted on the basis of theories for non-equilibrium relaxation.     

Nitrogen and phosphorus content of flow from drains fertilized with cow manure slurry

Summary The rate of flow and nitrate and phosphorus content of the water from four drained sandy and clayey plots of size 12×60 m cropped to continuous corn were determined following two annual applications of different rates (0, 260, 390 and 520 kg N/ha) of cow manure slurry. The drain flow was directly related to the rainfall and was greatly influenced by soil texture. The N losses were greater in 1972 (7.8 to 19.1 kg N/ha) than in 1971 (0.4 to 7.8 kg N/ha) because of more summer rainfall. Nitrogen and phosphorus losses were larger from the sandy plots than from the clayey plots. The manure application rates had no apparent effect on nitrogen losses in the drain water.     

Iron and Porphyrin Trafficking in Heme Biogenesis

Iron is an essential element for diverse biological functions. In mammals, the majority of iron is enclosed within a single prosthetic group: heme. In metazoans, heme is synthesized via a highly conserved and coordinated pathway within the mitochondria. However, iron is acquired from the environment and subsequently assimilated into various cellular pathways, including heme synthesis. Both iron and heme are toxic but essential cofactors. How is iron transported from the extracellular milieu to the mitochondria? How are heme and heme intermediates coordinated with iron transport? Although recent studies have answered some questions, several pieces of this intriguing puzzle remain unsolved.     

Risk assessment of heavy metal and metalloid toxicity through a contaminated vegetable (Cucurbita maxima) from wastewater irrigated area: A case study for a site-specific risk assessment in Jhang,Pakistan

The present research was conducted in district Jhang, Pakistan, to evaluate the concentration of metals/metalloids in soil and pumpkin (Cucurbita maxima) irrigated with domestic wastewater. Data revealed that the levels of metals and metalloids in soil samples from two different sites were below the safe limits except Cd, whereas, in the vegetable, the concentrations of As, Se, Ni, Mo, Pb, Mn, and Cu were above the safe limits. The levels of 12 metals and metalloids in the soil were ranged between 0.14 to 22.76 mg/kg at site-I and 0.16 to 22.13 mg/kg at site-II. The levels of these metals in the vegetable were found 0.35 to 61.13 mg/kg at site-I and 0.31 to 53.63 mg/kg at site-II. The transfer factor at both sites was highest for As and Co. The pollution load index recorded for Se, Cu, Cd, Mo, Pb, and Co was greater than 1. The daily intake of As, Mn, and Mo was above the oral reference dose, which reflects that the intake of pumpkin is not safe for the inhabitants of the selected sites. The control measures should be taken to phytoextract heavy metals and metalloids from polluted sites so as to reduce the health risks.     

A simple enzyme-linked immunosorbent assay for sex hormone-binding globulin

A simple enzyme-linked immunosorbent assay (ELISA) for sex hormone-binding globulin (SHBG) has been developed. Polyclonal antibody raised to SHBG purified to homogeneity was employed. The ELISA, which may be performed in under 4 h, shows no cross-reactivity with other serum proteins, has a sensitivity of less than 1.2 fmol per sample, demonstrates excellent correlation with ligand-binding techniques (r = 0.996; p less than 0.0001), and has intra- and inter-assay coefficients of variation of between 5-9% and 7-11% respectively.     

Enhancement of shoot regeneration potential by liquid medium culture from mature cotyledons of sunflower (Helianthus annuus L.)

We describe here a liquid culture system for the regeneration of shoots at high frequencies from mature cotyledon tissues of three genotypes of sunflower (Helianthus annuus L.) one of which had previously been found to be recalcitrant to regeneration when cotyledons were cultured on solid medium. Cotyledons were excised from 2-day-old seedlings and incubated in liquid Murashige and Skoog's modified medium supplemented with 5.4 M naphthaleneacetic acid (NAA) and 4.4 M benzylaminopurine (BAP). After two weeks in culture, the whole upper surface of regenerating explants was covered with green shootlets. The percentages of regenerating explants of three genotypes varied between 60 and 70%, and the number of shoots per regenerating explant was highly increased. The shootlets were transferred to solid Murashige and Skoog's medium allowing shoot development, then to rooting medium. Rooted plantlets were successfully acclimatized and gave fertile plants. The role of liquid medium culture in the induction of sunflower regeneration is discussed.Abbreviations BAP 6-benzylaminopurine - NAA 1-naphthaleneacetic acid - IAA indole-3-acetic acid - IBA indole-3-butyric acid     

Spinach-thylakoid phosphorylation: Studies on the kinetics of changes in photosystem antenna size, spill-over and phosphorylation of light-harvesting chlorophyll a/b protein

The kinetics of LHCP phosphorylation and associated changes in photosystem cross-section and energy ‘spill-over’ from PS II to PS I have been examined in isolated spinach chloroplasts. During an initial phosphorylation period of 3–6 min, in the presence of saturating concentrations of Mg²⁺, the increase in PS I and decrease in PS II cross-section are largely completed, as judged by both measurements of the steady-state redox state of Q and fluorescence yield changes. This corresponds to a period of rapid ³²P incorporation into the low-molecular weight LHCP polypeptide. Subsequent to this initial 3–6-min period there is substantial further phosphorylation of both LHCP polypeptides, which is not accompanied by significant changes in photosystem cross-section, even after the chloroplasts had been unstacked with extensive mixing of PS I and PS II by Mg-removal. It is suggested that there exists a specific ‘mobile’ population of LHCP molecules which is rapidly phosphorylated and which may be enriched in the low-molecular-weight polypeptide. In addition, measurements of the kinetics of the ‘spill-over’ changes upon either Mg²⁺ addition or removal indicate that the continued phosphorylation of LHCP is able to increase the ‘spill-over’ process under favourable ionic conditions.     

Microtubule-associated protein tau. A component of Alzheimer paired helical filaments

Microtubule-associated protein tau was purified from bovine brain microtubules by either (1) phosphocellulose chromatography, (2) heat treatment at pH 6.4, (3) heat treatment at pH 2.7, (4) heat treatment at pH 2.7 followed by extraction with perchloric acid and precipitation with glycerol, or (5) by precipitation with ammonium sulfate followed by extraction with perchloric acid. All of these tau preparations reacted specifically with antibodies to Alzheimer paired helical filaments. Affinity purified antibodies to tau labeled both Alzheimer neurofibrillary tangles and plaque neurites but not amyloid in Alzheimer brain tissue sections and labeled paired helical filament polypeptides on Western blots. Human brain tau and paired helical filament polypeptides co-migrated on sodium dodecyl sulfate-polyacrylamide gels. These results suggest that tau is a major component of Alzheimer paired helical filaments.     

Crystal structure of Boc-Ala-Aib-Ala-Aib-Aib-methyl ester,a pentapeptide fragment of the channel-forming ionophore suzukacillin

t-Buthyoxycarbonyl-L -alanyl-α-aminiosobutyryl-L -alanyl-α-aminoisobutyryl-α-aminoisobutyric acid methyl ester (t-Boc-L -Ala-Aib-L -Ala-Aib-Aib-OMe), C₂₄H₄₃N₅O₈, an end-protected pentapeptide with a sequence corresponding to the 6th through the 10th residues in suzukacillin, crystallizes in the orthorhombic space group P2₁2₁2₁ with a = 11.671, b = 14.534, c = 17.906 Å and z = 4. The molecule exists as a right-handed 3₁₀-helix with a pitch of 6.026 Å. The helix is stabilized by three 4 → 1 hydrogen bonds with the NH groups of Ala(3), Aib(4), and Aib(5) hydrogen bonding to the carbonyl oxygens of t-Boc, Ala(1), and Aib(2), respectively. The helical molecules arrange themselves in a head-to-tail fashion along the a direction in such a way that the NH groups of Ala(1) and Aib(2) hydrogen bond to the carbonyl oxygens of Aib(4) and Aib(5), respectively, of a translationally related molecule. The helical columns thus formed close-pack nearly hexagonally to form the crystal.