Acetylene inhibition technique underestimates in situ denitrification rates in intact cores of freshwater sediment

Abstract Denitrification in intact sediment cores was measured by the acetylene inhibition technique and compared with the nitrate flux between water and sediment. Less than half of the nitrate-N consumed by the sediment could be recovered as nitrous oxide-N. The low recovery rate of nitrous oxide from intact sediment cores indicated losses of nitrous oxide by diffusion down to nitrate-free sediment layers, where reduction of nitrous oxide may take place. In sediment slurries 100% of nitrate-N could be recovered as nitrous oxide-N as long as the nitrate concentration in the liquid phase was above 10 μM. Nitrous oxide added to nitrate-free sediment slurries was reduced regardless of whether acetylene was present or not. Therefore denitrification may be significantly underestimated by this method.     

Zur Ätiologie der Anreicherung von Aminosäuren und Amiden im Wurzelraum vonHelianthus Annuus L

Ohne ZusammenfassungMit 5 Textabbildungen     

EVOLUTIONARY RELATIONSHIPS BETWEEN FOUR SPECIES OF CLADOPHORA (CLADOPHORALES,CHLOROPHYTA) BASED ON DNA–DNA HYBRIDIZATION1

Analysis of the reassociation kinetics of the DNA from Cladophora pellucida (Huds.) Kütz. indicates that the genome of this benthic alga is comprised of approximately 75% repetitive sequences. Single-copy sequences reassociated with a rate constant of 1.8 × 10^?3 M^?1· s^?1, which corresponds to a haploid genome size of 4.7 × 10⁸ bp. Genotypic relationships between members of the form section Longiarticulatae were determined by the method of DNA–DNA hybridization. No significant divergence was observed between the single-copy sequences of C. pellucida isolates from the East Atlantic coast and Mediterranean Sea. Cladophora feredayi Harv. and C. att. ad pellucida from Australia and C. pellucidoidea van den Hoek from the West Atlantic coast were highly and about equally divergent from C. pellucida. The data support the hypothesis that the West Atlantic–West Pacific divergence reflects the middle Miocene closure of the Mediterranean–Indo-Pacific seaways, and the hypothesis that the Northwest Atlantic–Northeast Atlantic divergence reflects the middle Miocene thermal separation of these coasts.     

Phytohormones in needles of healthy and declining silver fir (Abies alba Mill.): I. Indole-3-acetic acid

 Levels of indole-3-acetic acid (IAA) were determined in needles from silver fir (Abies alba Mill.) trees in the northern Black Forest. IAA was quantified by gas chromatography (GC) as 1-heptafluorobutyryl-IAA-methylester (HFB-IAA-ME) using electron capture detection. Prior to GC analysis, extensive purification of needle extracts was performed employing two HPLC steps. Peak identity of HFB-IAA-ME was confirmed by combined gas chromatography-mass spectrometry in selected samples. Levels of IAA in needles belonging to different needle age-classes exhibited a cyclic seasonal pattern with highest concentrations in winter and lowest levels in spring when bud-break occurred. Such a cyclic seasonal pattern of IAA levels was also observed in needles from declining fir trees or fir trees suffering from a strong sulfur impact (S-impact) in the field due to a local SO₂ source. Levels of IAA increased with increasing needle age. This age dependency of IAA concentrations was most pronounced in late autumn when IAA levels were high and nearly disappeared in spring when IAA levels reached their minimum. In needles from declining fir trees or fir trees suffering from a strong S-impact in the field, IAA levels hardly increased with increasing needle age. It is suggested that in healthy trees high levels of IAA protect older needles from abscission and that the considerable losses of older needles of declining fir trees or of fir trees under S-impact are a consequence of the low levels of IAA found in older needles of such trees. Received: 4 May 1995 / Accepted: 29 August 1995     

Klinefelter's syndrome and incontinentia pigmenti Bloch-Sulzberger

Summary We report a newborn with incontinentia pigmenti Bloch-Sulzberger and male phenotype. Chromosome analysis revealed a Klinefelter's syndrome 47,XXY. These findings are compatible with the hypothesis of dominant sexlinked genes carried on the X-chromosome in this disease.

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Zusammenfassung Wir berichten über ein neugeborenes Kind mit männlichem Phänotyp bei Incontinentia pigmenti Bloch-Sulzberger. Bei der klinischen Abklärung fand sich die Gonosomenaberration eines Klinefelter-Syndroms 47,XXY. Dieser Befund geht konform mit der Vermutung eines dominant X-gekoppelten Erbganges dieser seltenen Hauterkrankung.

     

Formation of 2-methyltryptophan in the biosynthesis of thiostrepton: isolation of S-adenosylmethionine:tryptophan 2-methyltransferase

L-2-Methyltryptophan was found to be an intermediate in the biosynthesis of the antibiotic thiostrepton. It was isolated from growing cultures and resting cells of Streptomyces laurentii in trapping experiments after the application of labeled L-methionine or L-tryptophan. Its formation from L-tryptophan and S-adenosylmethionine was studied in a cell-free extract of S. laurentii. Although several attempts to purify the soluble methyltransferase by standard methods failed, some of its characteristics could be determined in the crude extract. The enzyme has a sharp pH optimum at pH 7.8. The apparent Km value for S-adenosylmethionine is 120 microM and the Ki value for S-adenosylhomocysteine is 480 microM. The enzyme is not stereoselective with respect to D- or L-tryptophan, but the D-isomer is converted at a slower rate than the L-isomer. Indolepyruvic acid is also methylated, while indole is not a substrate. The methyl group is transferred with retention of its configuration, contrary to most other methyltransferase reactions.     

Mechanistic studies on C-19 demethylation in oestrogen biosynthesis

Mechanistic aspects of the biosynthesis of oestrogen have been studied with a microsomal preparation from full-term human placenta. The overall transformation, termed the aromatization process, involves three steps using O₂ and NADPH, in which the C-19 methyl group of an androgen is oxidised to formic acid with concomitant production of the aromatic ring of oestrogen: [Formula: see text] To study the mechanism of this process in terms of the involvement of the oxygen atoms, a number of labelled precursors were synthesized. Notable amongst these were 19-hydroxy-4-androstene-3,17-dione (II) and 19-oxo-4-androstene-3,17-dione (IV) in which the C-19 was labelled with ²H in addition to ¹⁸O. In order to follow the fate of the labelled atoms at C-19 of (II) and (IV) during the aromatization, the formic acid released from C-19 was benzylated and analysed by mass spectrometry. Experimental procedures were devised to minimize the exchange of oxygen atoms in substrates and product with oxygens of the medium. In the conversion of the 19-[¹⁸O] compounds of types (II) and (IV) into 3-hydroxy-1,3,5-(10)-oestratriene-17-one (V, oestrone), it was found that the formic acid from C-19 retained the original substrate oxygen. When the equivalent ¹⁶O substrates were aromatized under ¹⁸O₂, the formic acid from both substrates contained one atom of ¹⁸O. It is argued that in the conversion of the 19-hydroxy compound (II) into the 19-oxo compound (IV), the C-19 oxygen of the former remains intact and that one atom of oxygen from O₂ is incorporated into formic acid during the conversion of the 19-oxo compound (IV) into oestrogen. This conclusion was further substantiated by demonstrating that in the aromatization of 4-androstene-3,17-dione (I), both the oxygen atoms in the formic acid originated from molecular oxygen. 10β-Hydroxy-4-oestrene-3,17-dione formate, a possible intermediate in the aromatization, was synthesized and shown not to be converted into oestrogen. In the light of the cumulative evidence available to date, stereochemical aspects of the conversion of the 19-hydroxy compound (II) into the 19-oxo compound (IV), and mechanistic features of the C-10–C-19 bond cleavage step during the conversion of the 19-oxo compound (IV) into oestrogen are discussed.