Gross Nitrogen Turnover of Natural and Managed Tropical Ecosystems at Mt. Kilimanjaro,Tanzania

In our study at Mt. Kilimanjaro, East Africa, we quantified gross rates of ammonification, nitrification, nitrogen immobilization, and dissimilatory nitrate reduction to ammonium in soils across different land uses, climate zones (savanna, montane forest ecosystems, extensive agroforest homegarden, and intensively managed coffee plantation), and seasons (dry, wet, and transition from dry to wet season) to identify if and to what extent conversion of natural ecosystems to cultivated land has affected key soil microbial nitrogen turnover processes. Overall variation of gross soil nitrogen turnover rates across different ecosystems was more pronounced than seasonal variations, with the highest turnover rates occurring at the transition between dry and wet seasons. Nitrogen production and immobilization rates positively correlated with soil organic carbon and total nitrogen concentrations as well as substrate availability of dissolved organic carbon and nitrogen r > 0.67, P < 0.05), but did not correlate with soil ammonium and nitrate concentrations. Soil nitrogen turnover rates were highest in the montane Ocotea forest (ammonification 29.84, nitrification 12.67, NH₄ ⁺ immobilization 38.92, NO₃ ^? immobilization 10.74, and DNRA 1.54 µg N g^?1 SDW d^?1) and progressively decreased with decreasing annual rainfall and increasing land-use intensity. Using indicators of N retention and characteristics of soil nutrient status, we observed a grouping of faster, but tighter N cycling in the (semi-) natural savanna and Ocotea forest. This contrasted with a more open N cycle in managed systems (the homegarden and coffee plantation) where N was more prone to leaching or gaseous losses due to high nitrate production rates. The partly disturbed (selected logging) lower montane forest ranged between these two groups.     

Increased cytotoxicity and decreased in vivo toxicity of FdUMP[10] relative to 5-FU.

The efficacy of treatment with 5-Fluorouracil (5-FU) is limited, in part, by its inefficient conversion to 5-Fluoro-2'-deoxyuridine-5'-O-monophosphate (FdUMP). We present data indicating that FdUMP[10], designed as a pro-drug for intracellular release of FdUMP, is cytotoxic as a consequence of uptake of the multimeric form. FdUMP[10] is stable in cell culture medium, with more than one-half of the material persisting as multimers of at least six nucleotides after a 48 h incubation at 37 degrees C. FdUMP[10] is more than 400 times more cytotoxic than 5-FU towards human colorectal tumor cells (H630). FdUMP[10] also has decreased toxicity in vivo, with doses as high as 200 mg/kg/day (qdx3) administered to Balb/c mice without morbidity, compared to a maximum tolerated dose of 45 mg/kg/day for 5-FU using the same protocol. FdUMP[10] shows reduced sensitivity to OPRTase- and TK-mediated drug resistance, relative to 5-FU and FdU, respectively, and is much more cytotoxic than 5-FU towards cells that overexpress thymidylate synthase. Thus, FdUMP[10] is less susceptible to resistance mechanisms that limit the clinical utility of 5-FU. The increased cytotoxicity, decreased toxicity in vivo, and reduced sensitivity to drug resistance of FdUMP[10], relative to 5-FU, indicates multimeric FdUMP is potentially valuable as an anti-neoplastic agent, either as a single agent, or in combination with 5-FU.     

Evaluation of genetic risks of alkylating agents. II. Haemoglobin as a dose monitor.

The degree of alkylation of haemoglobin was determined at different times after treatment of mice with one directly active alkylating agent, ethylene oxide, and one agent that requires metabolic activation, dimethylnitrosamine. Because of the random alkylation of red blood cells of various ages and the stability of alkylated haemoglobin, the amount of alkylated amino acids in haemoglobin decreases linearly with time, reaching the value zero after about 40 days, the life-span of erythrocytes in the mouse. This provides a basis for the use of haemoglobin as a monitor for integral doses of genotoxic environmental chemicals.     

Isolation,purification, and some of the properties of hemi-cellulase from fusarium sp.

An extracellular hemicellulase from a soil fungus (Fusarium sp.) grown on a medium containing groundnut hemicellulose B was purified 76-fold by ammonium sulphate fractionation, chromatography on DEAE-cellulose, and gel filtration on Sephadex G-100. It was found to be homogeneous by disc-gel electrophoresis at pH 8. It showed optimal activity at pH 5.6 and 37°. It was observed that groundnut and sesame hemicellulose B were degraded considerably (~80 and 58%, respectively) by the purified hemicellulase, whereas glucomannan and xylan from groundnut were comparatively poorly hydrolysed (~30–40%).     

Genetic potential,diversity and activity of an atrazine-degrading community enriched from a herbicide factory effluent

Aims: To characterize an atrazine-degrading bacterial community enriched from the wastewater of a herbicide factory. Methods and Results: The community mineralized 81·4 ± 1·9% of [¹⁴C-ring]atrazine and 31·0 ± 1·8% of [¹⁴C-ethyl]atrazine within 6 days of batch cultivation in mineral salts medium containing atrazine as the sole nitrogen source. Degradation activity of the community towards different chloro- and methylthio-substituted s-triazine compounds was also demonstrated. Restriction analysis of amplified 16S rDNA revealed high diversity of bacterial populations forming the community, with Pseudomonas species dominating in the clone library. Atrazine-degrading genetic potential of the community determined by PCR revealed the presence of trzN, atzB, atzC and trzD genes. The trzN, atzB and atzC genes were shown to be located on a plasmid of 322 kb. Quantitative PCR showed that relative abundances of atzB, atzC and trzD genes were approx. 100-fold lower than 16S rDNA. Conclusions: The enriched community represents a complex bacterial association expressing substantial atrazine-mineralizing activity and a broad specificity towards a range of s-triazine compounds. Significance and Impact of the Study: Our study is beginning to yield insights into the richness, genetic potential and density of functional atrazine-mineralizing community that could be a potential bioaugmentation agent for improving biotransformation processes in wastewaters bearing different s-triazine compounds.     

Dehydro-enkephalins. VIII. Attempted synthesis of dehydrotyrosine-enkephalins

Two kinds of dehydropeptide analogs of enkephalin containing a delta Tyr unit at the N-terminus have been synthesized by coupling Boc-delta Tyr-(Cl2 Bzl)-OH with amino acid amides and tetrapeptide esters using the water soluble carbodiimide-HOBt method. Pentapeptides consisting of delta Tyr1, and delta Phe4 or delta Leu5 were also prepared. Ultraviolet difference spectroscopy was important in the characterization of the dehydro moieties, delta Tyr, delta Phe and delta Leu. Attempts to liberate delta Tyr1-enkephalins have been unsuccessful because of the instability of an N-terminal delta Tyr residue having p-phenolic group in the side chain.     

Baboon cytochrome P450 17alpha-hydroxylase/17,20-lyase (CYP17).

Human cytochrome P450 17alpha-hydroxylase (CYP17) catalyses not only the 17alpha-hydroxlation of pregnenolone and progesterone and the C17,20-side chain cleavage (lyase) of 17alpha-hydroxypregnenolone, necessary for the biosynthesis of C21-glucocorticoids and C19-androgens, but also catalyses the 16alpha-hydroxylation of progesterone. In efforts to understand the complex enzymology of CYP17, structure/function relationships have been reported previously after expressing recombinant DNAs, encoding CYP17 from various species, in nonsteroidogenic mammalian or yeast cells. A major difference between species resides in the lyase activity towards the hydroxylated intermediates and in the fact that the secretion of C19-steroids take place, in some species, principally in the gonads. Because human and higher primate adrenals secrete steroids, CYP17 has been characterized in the Cape baboon, a species more closely related to humans, in an effort to gain a further understanding of the reactions catalysed by CYP17. Baboon and human CYP17 cDNA share 96% homology. Baboon CYP17 has apparent Km and V values for pregnenolone and progesterone of 0.9 micro m and 0.4 nmol.h-1.mg protein-1 and 6.5 micro m and 3.9 nmol.h-1.mg protein-1, respectively. Baboon CYP17 had a significantly higher activity for progesterone hydroxylation relative to pregnenolone. No 16alpha-hydroxylase and no lyase activity for 17alpha-hydroxyprogesterone. Sequence analyses showed that there are 28 different amino acid residues between human and baboon CYP17, primarily in helices F and G and the F-G loop.