CU(II)-catalyzed oxidation of Alzheimer's disease beta-amyloid peptide and related sequences: remarkably different selectivities of neurotoxic betaAP1-40 and non-toxic betaAP40-1.

We investigated the CuII-catalyzed oxidation of beta-amyloid peptides betaAP10-20 and betaAP40-1 by tandem mass spectrometry and compared oxidation yields and selectivities to those for betaAP1-16, betaAP1-28 and betaAP1-40, which were obtained earlier (26). While betaAP1-16, betaAP1-28 and betaAP1-40 showed an almost exclusive oxidation of His residues to 2-oxo-histidine, the selectivity pattern is changed for betaAP10-20,which shows oxidation of His but also hydroxylation of Tyr and Phe. In contrast to betaAP1-40, the reverse sequence betaAP40-1 shows a strong selectivity for the hydroxylation of Tyr31 while only negligible His oxidation is observed at early time points. These selectivity patterns show the importance of the geometry of the metal-binding site for peptide/protein oxidation. The significantly different characteristic of betaAP1-40 and betaAP40-1 with regard to metal catalyzed processes may be related to the differences in the neurotoxic properties of these sequences.     

Single-cell investigation by laser scanning confocal microscopy of cytochemical alterations resulting from extracellular oxidant challenge

Confocal laser scanning fluorescence microscopy coupled to image analysis was employed in order to develop and evaluate procedures for the appraisal at the single-cell level of: (1) protein-bound 4-hydroxynonenal, the specific product of membrane peroxidation (by means of immunocytochemistry with biotin-avidin revelation); (2) protein oxidation (by reaction of protein carbonyls with 2,4-dinitrophenyl-hydrazine followed by immunocytochemistry of dinitrophenyl moieties); and (3) cellular protein thiols (by direct alkylation of sulfhydryl groups with thiol-specific fluorescent reagents possessing different cell permeabilities). The procedures proved able to reveal the subcellular distribution of cytochemical parameters useful as indices of oxidative stress conditions, and may allow redox phenotyping of isolated cells, which would provide an efficient tool in selected experimental models.     

The role of active oxygen in iron tolerance of rice (Oryza sauva L.)

Summary Iron tolerance of rice (Oryza sativa L.) was investigated using an oxygen depleted hydroculture system. Treatment with high concentrations of Fe²⁺ induced yellowing and bronzing symptoms as well as iron coatings at the root surface. Root and shoot growth were inhibited by increasing iron concentration in the medium. All symptoms were more pronounced in an iron sensitive cultivar (IR 64) compared to an iron tolerant one (IR 9764-45-2). Superoxide dismutase and peroxidase activity of root extracts of IR 97 were about twice that of IR 64 in untreated control plants. No significant increase of peroxidase activity was detected with increasing iron concentration in the medium. Catalase activity of IR 64 was slightly higher than that of IR 97, independent of iron concentration.Abbreviations SOD Superoxide dismutase (EC 1.15.1.1) - POD peroxidase (EC 1.11.1.7) - EDTA ethylenediamintetraacetic acid - fwt fresh weight - Hepes (N-[2-hydroxyethyl]piperazine-N-[2-ethanesulfonic acid]) - BSA bovine serum albumin - IR 97 IR 9764-45-2 an iron tolerant rice cultivar - IR 64 iron sensitive rice cultivar - PM plasma membrane     

Liming induced stimulation of the amino acid metabolism in mycorrhizal roots of Norway spruce (Picea abies [L.] Karst.)

Localization and activity of three enzymes involved in the amino acid metabolism of ectomycorrhizas were investigated within an interdisciplinary experiment performed in a mature Norway spruce stand in Southern Germany (Höglwald). The enzymes NAD-glutamate dehydrogenase and aspartate aminotransferase were present in root cells, whereas aminopeptidase was found in mycorrhizas of Norway spruce such as Piceirhiza nigra and those with the fungi Cenococcum geophilum, Elaphomyces sp., Russula ochroleuca and Tylospora sp. Mycorrhizas growing in the humus layer contained about double the amount of protein found in those taken from the upper mineral soil (0–5 cm).Acid irrigation of the soil had no effect on the activity of any of the investigated enzymes, soluble protein or total N-contents irrespective of whether roots were taken from the organic layer or from the upper mineral soil. Liming, however, stimulated the activity of the three enzymes in mycorrhizas of the organic layer (O_f+O_h) whereas it had no effect on the activity of the investigated enzymes of mycorrhizas in the upper mineral soil. This effect is attributed to increased contents of soluble organic nitrogen compounds in the soil of the limed plots as compared to the unlimed plots.     

Response of rice varieties to soil salinity and air humidity: A possible involvement of root-borne ABA

In a phytotron experiment four rice varieties (Pokkali, IR 28, IR 50, IR 31785-58-1-2-3-3) grown in individual pots were subjected to low (40/55% day/night) and high (75/90%) air humidity (RH), while soil salinity was gradually increased by injecting 0, 30, 60 or 120 mM NaCl solutions every two days. Bulk root and stem base water potential (SWP), abscisic acid (ABA) content of the xylem sap and stomatal resistance (rs) of the youngest fully expanded leaf were determined two days after each salt application. The SWP decreased and xylem ABA and rs increased throughout the 8 days of treatment. The effects were amplified by low RH. A chain of physiological events was hypothesized in which high soil electric conductivity (EC) reduces SWP, followed by release of root-borne ABA to the xylem and eventually resulting in stomatal closure. To explain varietal differences in stomatal reaction, supposed cause and effect variables were compared by linear regression. This revealed strong differences in physiological reactions to the RH and salt treatments among the test varieties. Under salt stress roots of IR 31785-58-1-2-3-3 produced much ABA under low RH, but no additional effect of low RH on rs could be found. By contrast, Pokkali produced little ABA, but rs was strongly affected by RH. RH did not affect the relationships EC vs. SWP and SWP vs. ABA in Pokkali, IR 28, and IR 50, but the relationship ABA vs. rs was strongly affected by RH. In IR 31785-58-1-2-3-3 RH strongly affected the relationship SWP vs. ABA, but had no effect on ABA vs. rs and EC vs. rs. The results are discussed regarding possible differences in varietal stomatal sensitivity to ABA and their implications for varietal salt tolerance.     

Enzyme activity measurements on isolated organs of Brachionus plicatilis (Rotifera)

A method is described by which the integument of Brachionus plicatilis, together with its intracellular lamina, is quickly dissolved before other parts or tissues of the animal are destroyed. After removing the integument several parts of the body can be separated and fractionated in a more or less intact state by centrifugation in a Percoll gradient. The measurement of enzyme activities has indicated that this procedure might provide a way of localizing enzymes within the rotifer body.     

Synthesis of some racemicγ-fluoro-α-amino acids

Summary Versatile three-step procedures for syntheses of seven racemi-fluoro-a-amino acids are described. Alkylation oftert-butyl N-(diphenylmethylene) glycinate with 1-bromo-2-fluoroalkanes gave N-protected aminoacid esters both in anhydrous medium using lithium-diisopropylamide as base at low temperature or in a two phase system of 50% aqueous sodium hydroxide and methylene chloride with triethylbenzylammonium chloride as the phase transfer catalyst at room temperature. Subsequent two-step deprotection with citric acid and hydrochloric acid gave the title compounds in 13–33% overall yields.Dedicated to Professor Dr.mult., Dr.h.c. Alois Haas on the occasion of his 65th birthday