Experimental investigations of multiple steady states in aerobic continuous cultivations of Saccharomyces cerevisiae

The steady-state behavior of a glucose-limited, aerobic, continuous cultivation of Saccharomyces cerevisiae CEN.PK113-7D was investigated around the critical dilution rate. Oxido-reductive steady states were obtained at dilution rates up to 0.09 h(-1) lower than the critical dilution rate by operating the bioreactor as a productostat, where the dilution rate was controlled on the basis of an ethanol measurement. Thus, the experimental investigations revealed that multiple steady states exist in a region of dilution rates below the critical dilution rate. The existence of multiple steady states was attributed to two distinct physiological effects occurring when growth changed from oxidative to oxido-reductive: (i) a decrease in the efficiency of ATP production and utilization (at ethanol concentrations below 3 g/L) and (ii) repression of the oxidative metabolism (at higher ethanol concentrations). The first effect was best observed at low ethanol concentrations, where multiple steady states were observed even when no repression of the oxidative metabolism was evident, i.e., the oxidative capacity was constant. However, at higher ethanol concentrations repression of the oxidative metabolism was observed (the oxidative capacity decreased), and this resulted in a broader range of dilution rates where multiple steady states could be found.     

Adenovirus-mediated expression of pig α(1,3) galactosyltransferase reconstructs Gal α(1,3) Gal epitope on the surface of human tumor cells

INTRODUCTIONGal a(1, 3) Gal (gal epitope) is a carbohydrate epitope, which is produced in large amounton the cells of pigs, mice and New World monkey(monkey of South America) by the glycosylationenzyme G alal 1 ) 4G IcNAc3- a- D- galactosyltransferase[or(1, 3)GT; EC2.4.1.511111. This enzyme is active in the Golgi appaxatus of cells and transfers galactose from the sugandonor uridine diphoSphate galactose (UDP-galactose) to the acceptor Nacetyllactosamine residue (Galaal-4GlcNAc-R…     

杉木与伴生植物凋落物混合分解的相互作用研究

通过对杉木与9种伴生植物凋落物混合分解特征比较研究表明,8种植物对杉木凋落物的分解均有不同程度的促进作用,其中观音座莲对杉木凋落物分解的促进最大,而木荷对杉木凋落物分解的影响则表现出先有一定程度的促进而后又有微弱的抑制作用,促进大小表现出观音座莲＞杜茎山＞三龙爪＞狗脊＞苎麻＞丝栗栲＞闽粤栲＞芒萁。杉木 落物反过来对木荷和闽粤栲凋落物有一些抑制作用,而对丝栗栲则有一些促进作用,但这种相互作用未达到显著差异水平。说明杉木与某些伴生植物种类的凋落物在混合分解过程中存在着相互作用的现象,因此,合理保护和恢复林下植物对加快杉木人工林生态系统的养分循环和地力维护具有重要的意义。     

Reduced endothelial nitric oxide synthase in lungs of chronically ventilated preterm lambs

Nitric oxide (NO), produced in lung vascular endothelium and airway epithelium, has an important role in regulating smooth muscle cell growth and tone. Chronic lung disease, a frequent complication of premature birth, is characterized by excess abundance, tone, and reactivity of smooth muscle in the pulmonary circulation and conducting airways, leading to increased lung vascular and airway resistance. Whether these structural and functional changes are associated with diminished pulmonary expression of endothelial nitric oxide synthase (eNOS) protein is unknown. Both quantitative immunoblot analysis and semiquantitative immunohistochemistry showed that there was less eNOS protein in the endothelium of small intrapulmonary arteries and epithelium of small airways of preterm lambs that were mechanically ventilated for 3 wk compared with control lambs born at term. No significant differences were detected for other proteins (inducible NOS, alpha-smooth muscle actin, and pancytokeratin). Lung vascular and respiratory tract resistances were greater in the chronically ventilated preterm lambs compared with control term lambs. These results support the notion that decreased eNOS in the pulmonary circulation and respiratory tract of preterm lambs may contribute to the pathophysiology of chronic lung disease.     

Lipopolysaccharide and interferon-gamma-induced nitric oxide production and protein oxidation in mouse peritoneal macrophages are affected by glutathione peroxidase-1 gene knockout

This study investigated the role of glutathione peroxidase-1 (GPX1) in protein oxidation in peritoneal macrophages. Macrophages isolated from both wild-type (WT) and GPX1 knockout (KO) mice were activated by lipopolysaccharide (LPS, 1 microg/ml) and interferon-gamma (IFN, 10 U/ml for 24 or 48 h in the presence or absence of 1 microM diquat (DQ), 250 microM aminoguanidine (AG, an inhibitor of inducible nitric oxide synthase), and (or) 100 microM diethyldithiocarbamate (DETC, an inhibitor of Cu,Zn-SOD). In the KO macrophages, there was no protein band detected by Western blot with anti-GPX1 antibody and 98% reduction in total GPX activity compared with WT cells. Nitric oxide (NO) synthesis was greatly enhanced after 24 h by GPX1 knockout and DQ, but inhibited by AG or DETC. Protein carbonyl formation in total cell extract was clearly associated with NO synthesis as higher levels of protein carbonyl were detected in activated KO than WT macrophages, and DQ enhanced slightly while AG or DETC virtually blocked its formation. A similarly marginal effect of GPX1 KO was observed on protein nitration. The LPS/IFN/DQ-induced DNA fragmentation was blocked by AG, but not by DETC. Cell viability at 48 h was decreased by the LPS/IFN activation and further reduced by the addition of DQ, but restored by AG. In conclusion, GPX1 affects the NO production in activated peritoneal macrophages and protects these cells against NO-associated protein oxidation.     

Evidence that NOS2 acts as a trigger and mediator of late preconditioning induced by acute systemic hypoxia

Chronic systemic hypoxia (SH) enhances myocardial ischemic tolerance in mammals. We studied the delayed cardioprotection caused by acute SH and associated signaling mechanism. Conscious adult male mice were exposed to one or two cycles of hypoxia (H; 10% O(2)) or normoxia (21% O(2)) for various durations (30 min, 2 h, 4 h) followed by 24 h of reoxygenation. Hearts were isolated 24 h later and subjected to ischemia-reperfusion in a Langendorff model. Infarct size was reduced in mice pretreated with one (H4h) or two cycles (H4hx2) of 4 h SH compared with normoxia mice (P < 0.05), which was abolished by an inducible nitric oxide synthase (NOS2) inhibitor (S-methylisothiourea, 3 mg/kg) given before SH or ischemia. H4hx2 also failed to reduce infarct size in NOS2 knockout mice. Cyclooxygenase-2 (COX-2) inhibitor (NS-398, 10 mg/kg) did not block the protection given either before H4hx2 or ischemia. A two- to three fold increase in myocardial NOS2 expression was observed in H4h, H2hx2, and H4hx2 (P < 0.05), whereas endothelial NOS (NOS3) or COX-2 remained unchanged. We conclude that acute SH induces delayed cardioprotection, which is triggered and mediated by NOS2, but not by NOS3 or COX-2.     

Cooperative binding of single-stranded telomeric DNA by the Pot1 protein of Schizosaccharomyces pombe

The fission yeast Pot1 (protection of telomeres) protein is a single-stranded telomeric DNA-binding protein and is required to protect the ends of chromosomes. Its N-terminal DNA-binding domain, Pot1pN, shows sequence similarity to the first OB fold of the telomere-binding protein alpha subunit of Oxytricha nova. The minimal-length telomeric ssDNA required to bind Pot1pN was determined to consist of six nucleotides, GGTTAC, by gel filtration chromatography and filter-binding assay (K(D) = 83 nM). Pot1pN is a monomer, and each monomer binds one hexanucleotide. Experiments with nucleotide substitutions demonstrated that the central four nucleotides are crucial for binding. The dependence of Pot1pN-ssDNA binding on salt concentration was consistent with a single ionic contact between the protein and the ssDNA phosphate backbone, such that at physiological salt condition 83% of the free energy of binding is nonelectrostatic. Subsequent binding experiments with longer ssDNAs indicated that Pot1pN binds to telomeric ssDNA with 3' end preference and in a highly cooperative manner that mainly results from DNA-induced protein-protein interactions. Together, the binding properties of Pot1pN suggest that the protein anchors itself at the very 3' end of a chromosome and then fills in very efficiently, coating the entire single-stranded overhang of the telomere.     

Semiochemicals from ovaries of gravid females attract ovipositing female houseflies,Musca domestica

Chemical signals originating from the ovaries of gravid females of Musca domestica (Diptera: Cyclorrhapha: Muscidae) attract ovipositing females to common egg-laying sites. Behavioral experiments indicated that females preferred to oviposit in fermented wheat bran containing ovaries from reproductively mature houseflies. Females preferred to oviposit in fermented wheat bran than wet wheat bran. This effect was additive with the attraction to housefly ovaries. Solvent extracts from housefly ovaries were attractive to gravid females. Extracts obtained with hexane were most attractive to gravid females for egg laying, and extracts obtained with ethyl acetate attracted more egg laying than extracts obtained by dichloromethane. Gas chromatography (GC) and gas chromatography coupled with mass spectrometry (GC-MS) analysis showed that tricosane and (Z)-9-tricosene were the main components of the hexane extracts. Both tricosane and (Z)-9-tricosene were shown to elicit dose-dependent aggregation of gravid females in oviposition bioassays, but high doses of either chemical were not attractive.