Biotransformation of diphenyl ether by the yeastTrichosporon beigelii SBUG 752

Trichosporon beigelii SBUG 752 was able to transform diphenyl ether. By TLC, HPLC, GC, GC-MS, NMR- and UV-spectroscopy, several oxidation products were identified. The primary attack was initiated by a monooxygenation step, resulting in the formation of 4-hydroxydiphenyl ether, 2-hydroxydiphenyl ether and 3-hydroxydiphenyl ether (48:47:5). Further oxidation led to 3,4-dihydroxydiphenyl ether. As a characteristic product resulting from the cleavage of an aromatic ring, the lactone of 2-hydroxy-4-phenoxymuconic acid was identified. The possible mechanism of ring cleavage to yield this metabolite is discussed.     

Kinetic studies of phenol degradation by Rhodococcus sp. P1 II. Continuous cultivation

The degradation of phenol by Rhodococcus sp. P1 was studied in continuous culture systems. The organism could be adapted by slowly increasing concentration, step by step, up to 30.0 g · 1^-1 phenol in the influent. The degradation rate reached values of about 0.3 g · g dry mass^-1 ·h^-1. Large step increases in phenol concentration and addition of further substrates (e.g., catechol) were tolerated up to a certain concentration. With increasing dilution rate and increasing inlet phenol concentration the stability of the system decreased.     

Enumeration of anaerobic oxalate-degrading bacteria in the ruminal contents of sheep

Abstract Concentrations of oxalate-degrading anaerobes in ruminal contents of sheep were determined from counts of colonies producing clear zones on a calcium oxalate medium (D agar with 7 mM CaCl₂). Viable counts of oxalate degraders from a 55-kg sheep fed a diet containing 32% halogeton (4.6% oxalate) averaged 2.6 × 10⁶/ g (dry weight). When the halogeton concentration in the diet was reduced to 16%, counts of oxalate degraders decreased nearly 300-fold. Oxalate-degrading isolates from this sheep were similar to OxB, the type strain of Oxalobacter formigenes . When a 45-kg sheep was fed diets containing 2.2, 1.5, and 0.8% oxalate, viable counts of oxalate degraders (enumerated on D agar with 14 mM CaCl₂ and 20% filter-sterilized ruminal fluid) represented 0.85, 0.52, and 0.06% of the total viable population, respectively; total viable counts were essentially unchanges by these concentrations of dietary oxalate. Similar percentages of oxalate degraders were also observed when a 23-kg sheep was fed diets containing 1.5 or 0.8% oxalate. This report presents the first direct measurements of the concentrations of oxalate-degrading bacteria in the rumen and supports the concept that the availability of oxalate in the diet influences the proportion of oxalate-degrading bacteria in the rumen     

Protein Bodies in the Pine Megagametophyte in vitro Culture: Ultrastructural, Histochemical and Electrophoretic Observations

The megagametophytes of the European black pine (Pinus nigra Arn.) were cultured on modified MS medium. After 10 d, protein bodies showed well-marked degradation on freeze-etched replicas and in preparations observed by scanning electron microscopy. After 20 d of cultivation, the megagametophyte cells were completely empty. Proteins secreted into the agar medium were determined by electrophoresis and 15 different proteins, in the range of 6.5 to 71 kDa, were identified.     

Turnover of D1 Protein Encoded by psbA Gene in Higher Plants and Cyanobacteria Sustains Photosynthetic Efficiency to Maintain Plant Productivity Under Photoinhibitory Irradiance

The photosynthesis and related plant productivity aspects of plants and cyanobacteria depend upon the functioning of photosystem 2 (PS2), associated with D1 and D2 heterodimer reaction centre core proteins. The D1 protein is encoded by psbA gene, genetically localized on the plastid genome (cpDNA), contains functional cofactors of PS2 in association with D2 protein, and also functions for radiant energy transformation through oxidation of water and reduction of plastoquinone. Surprisingly, D1 protein accounts for even less than 1% of the total thylakoid membrane protein content. In spite of that, its rate of turnover is very much comparable to ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) large subunit, most abundantly present in green tissue. The normal functioning of PS2 possesses damage-repair cycles of D1 protein. Generally, rate of photodamage does not exceed the rate of repair under optimal growth conditions, therefore, no adverse effect on photosynthetic efficiency is manifest. However, under strong irradiance coupled with elevated temperature, level of photodamage exceeds the rate of repair, resulting in photoinhibition, photodegradation of D1 protein, and lowering photosynthetic efficiency linked with plant productivity eventually. The features of D1 turnover process are reviewed, particularly with respect to molecular mechanisms.     

A novel alkaline α-galactosidase gene is involved in rice leaf senescence

We previously isolated and identified numerous senescence-associated genes (SAGs) in rice leaves. Here we characterized the structure and function of an SAG-Osh69 encoding alkaline α-galactosidase that belongs to a novel family of glycosyl hydrolases. Osh69 is a single-copy gene composed of 13 exons located on rice chromosome 8. The expression level of Osh69 is not only up-regulated during natural leaf senescence but also induced rapidly by darkness, hormones (methyl jasmonic acid, salicylic acid), and stresses (H₂O₂ and wounding). The recombinant Osh69 protein over-expressed in Escherichia coli has displayed optimal α-galactosidase activity at pH 8.0. The enzyme showed good hydrolytic activities towards α-1,6-galactosyl oligosaccharides and galactolipid digalactosyl diacylglycerol. Immunoelectron microscopic analysis demonstrates that Osh69 is specifically localized in the chloroplasts of senescing leaves. These findings strongly suggest an important role for Osh69 in the degradation of chloroplast galactolipids during leaf senescence. The nucleotide sequence data reported will appear in the GenBank Nucleotide Sequence Database under the accession number AF251068.     

Dis3‐like 1: a novel exoribonuclease associated with the human exosome

The exosome is an exoribonuclease complex involved in the degradation and maturation of a wide variety of RNAs. The nine‐subunit core of the eukaryotic exosome is catalytically inactive and may have an architectural function and mediate substrate binding. In Saccharomyces cerevisiae, the associated Dis3 and Rrp6 provide the exoribonucleolytic activity. The human exosome‐associated Rrp6 counterpart contributes to its activity, whereas the human Dis3 protein is not detectably associated with the exosome. Here, a proteomic analysis of immunoaffinity‐purified human exosome complexes identified a novel exosome‐associated exoribonuclease, human Dis3‐like exonuclease 1 (hDis3L1), which was confirmed to associate with the exosome core by co‐immunoprecipitation. In contrast to the nuclear localization of Dis3, hDis3L1 exclusively localized to the cytoplasm. The hDis3L1 isolated from transfected cells degraded RNA in an exoribonucleolytic manner, and its RNB domain seemed to mediate this activity. The siRNA‐mediated knockdown of hDis3L1 in HeLa cells resulted in elevated levels of poly(A)‐tailed 28S rRNA degradation intermediates, indicating the involvement of hDis3L1 in cytoplasmic RNA decay. Taken together, these data indicate that hDis3L1 is a novel exosome‐associated exoribonuclease in the cytoplasm of human cells.     

Mechanisms and pathogenesis of thyroid cancer in animals and man

The transformation of the normal fully differentiated thyroid follicular cell to the rapidly growing undifferentiated anaplastic thyroid carcinoma cell involves a number of stages which have been defined morphologically and are now being related to various growth pathways and to molecular biological defects. The two main factors involved in this transformation are growth stimulation and mutagenesis. Growth stimulation alone, through elevated TSH, can lead to the development of thyroid tumours, usually benign, and retaining TSH dependency in some cases. Mutagens alone, if growth is suppressed, do not produce tumours, the combination of mutagens and increased growth is a potent carcinogenic regime. Non-genotoxic carcinogenesis in the thyroid involves growth, without mutagenesis the agent often causes this through affecting one component of thyroid hormone synthesis or metabolism, leading to a fall in thyroid hormone levels and a rise in TSH. Growth stimulation increases the rate of cell division, and therefore increases the chance of a mutation. Continued growth increases the change of subsequent events, in particular loss of heterozygosity in a tumour suppressor gene. The main oncogenes involved in human thyroid carcinogens are ras in the follicular tumour pathway, and ret in the papillary carcinoma pathway. p53 is involved in the progression of either papillary or follicular adenoma to an undifferentiated carcinoma. In experimental thyroid carcinogenesis, ras is again involved, with a link between the mutagenic agent used and the type of ras gene showing mutation. Analysis of the involvement of different growth factors and oncogenes in thyroid carcinogenesis suggests that genes related to the two receptors concerned with normal TSH stimulated growth, TSH receptor and the IGF1 recpptor may be involved in the progression of thyroid tumours of follicular pathology. Several tyrosine kinase receptors with unknown ligands or of uncertain physiological function are linked to papillary carcinoma. The recent large increase in papillary carcinoma of the thyroid in children exposed to fallout from the Chernobyl nuclear accident underlines the importance of understanding the pathobiology of thyroid neoplasia.