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141.
Nitrogenous excretion in two snails, Littorina saxatilis (high intertidal) and L. obtusata (low intertidal) was studied in relation to temperature acclimation (at 4° and 21°C), including total N excretion rates,
the fraction of urea in N excretion, corresponding O:N ratios and the partitioning of deaminated protein between catabolic
and anabolic processes at 4°, 11° and 21°C. Aggregate N excretion rates in both species showed no significant compensatory
adjustments following acclimation. Total weight specific N excretion rates at 21°C were higher in standard 3 mg L. saxatilis (739 ng N mg−1 h−1) than standard 5 mg L. obtusata (257 ng N mg−1 h−1) for snails acclimated to 21°C. Comparisons of Q10 values of total weight specific N excretion to Q10 values for weight specific oxygen consumption ({xxV}O2) between 4° to 11 °C and 11° to 21°C indicated that, while total rates of catabolic metabolism ({xxV}O2) and protein deamination in L. obtusata were essentially parallel, the relationship between N excretion and {xxV}O2 in L. saxatilis revealed the partitioning of a larger share of deaminated protein carbon into anabolism at 4° and 21°C than at 11°C. Urea
N accounted for a larger share of aggregate N excreted in L. saxatilis than in L. obtusata, but in both species urea N is a greater proportion of total N excreted when acclimated at 4°C (urea N: ammonia N ratio range:
1 to 2.15) than in snails acclimated to 21°C (urea N: ammonia N ratio range: 0.46 to 1.39). Molar O:N ratios indicate that
the proportion of metabolism supported by protein catabolism is greater in L. saxatilis (O:N range: 2.5–8.4) than in L. obtusata (O:N range: 7.3–13.0). In both species, regardless of acclimation temperature, the O:N ratios are generally lowest (high
protein catabolism) at 4°C and highest at 21°C. 相似文献
142.
Christelle David Laurent Bischoff Hervé Meudal Catherine Llorens-Cortes Bernard Pierre Roques Marie-Claude Fournié-Zaluski 《Letters in Peptide Science》1997,4(4-6):411-414
In order to study the physiological role of aminopeptidase A (APA),several -mercapto--amino acyl dipeptides were synthesized toobtain compounds having a high affinity for APA and a high selectivityversus aminopeptidase N (APN). Sulfonamide and carboxylate moieties whichhave been shown to be recognized by the S1 subsite of theenzyme were introduced on the side chain of the -mercapto--aminoacyl sub-unit, the latter being coupled to dipeptides optimized to interactwith the S1 andS2 subsites by means of combinatorialchemistry. Good affinities (16 nM) were obtained, the selectivity factorsbeing up to 160-fold versus APN. 相似文献
143.
在体外系统中,发现超氧化物歧化酶(SOD)具有切割超螺旋DNA的活性. 猪血和牛血Cu/Zn-SOD以及烟草Mn-SOD都能将超螺旋DNA转变为非超螺旋结构的缺刻环状DNA,进一步产生线状DNA. 它们只作用于超螺旋DNA而不作用于线状DNA. 这个事实排除了SOD样品中污染核酸酶的可能性. 用H2O2、胍基抑制或蛋白酶降解的实验结果表明,这两种酶的活性中心处于酶蛋白的不同部位. 相似文献
144.
The nitrogen budget in the rotifer Brachionus rotundiformis wasmeasured by the stable-isotope technique. The budget was estimatedusing the difference in the turnover time between egestion andexcretion. The rotifer was fed on the algae Nannochloropsiswhich was labeled with 15N as a tracer. The turnover time ofegestion and excretion were 20 min and 2.5 hours, respectively. Where77% of the ingested nitrogen was egested, and of the assimilated23%, 18% were devoted to growth and 5% to excretion.As for the unassimilated nitrogen egested as faeces, it recycled tothe rotifer through bacteriovory. When the algae provided as foodwere almost fully consumed, bacteriovory became dominant. Thethreshold occurred when the concentration of algae in the culture wasbetween 1.5 and 0.5 million cells of Nannochloropsis per ml. Ina chemostat operated with un-limited food condition, bacterialnitrogen corresponding to 20% of algal feeding, was consumed by therotifer.In a semi-continuous mass culture where food condition was limited,bacteriovory was more effective in supporting the rotiferreproduction. It contributed to the extremely high nitrogen recoveryfrom the provided foods (algae and oil-yeast) to the harvestedrotifers. The rapid and large nitrogen outflow from rotifersaccelerated the propagation of edible bacteria and can explain thestrange paradox observed in the culture; daily supply of foods didnot cover the sum of growth and excretion.It is not too exaggerated to state that the rotifer mass culture issupported by bacteria. The future strategy for maintenance of masscultures should consider this aspect. 相似文献
145.
Selective Changes in Cell Bodies and Growth Cones of Nerve Growth Factor-Differentiated PC12 Cells Induced by Chemical Hypoxia 总被引:2,自引:1,他引:1
Abstract: Cytosolic free Ca2+ concentration ([Ca2+]i) was measured in differentiated PC12 cells to test whether chemical hypoxia selectively alters intracellular Ca2+ in growth cones and cell bodies. Hypoxia increased [Ca2+]i and exaggerated its response to K+ depolarization in both parts of the cells. [Ca2+]i in the cell bodies was greater than that in the growth cones under resting conditions and in response to K+ or hypoxia. Ca2+-channel blockers selectively altered these responses. The L-channel blocker nifedipine reduced [Ca2+]i following K+ depolarization by 67% in the cell bodies but only 25% in the growth cones. In contrast, the N-channel blocker ω-conotoxin GVIA (ω-CgTX) diminished K+-induced changes in [Ca2+]i only in the growth cones. During hypoxia, nifedipine was more effective in the cell bodies than in the growth cones. During hypoxia, ω-CgTX diminished K+-induced changes by 50–75% in both parts of the cell, but only immediately after depolarization. The combination of nifedipine and ω-CgTX diminished the [Ca2+]i response to K+ with or without hypoxia by >90% in the cell body and 70% in the growth cones. Thus, the increased Ca2+ entry with K+ during hypoxia is primarily through L channels in the cell bodies, whereas in growth cones influx through L and N channels is about equal. The results show that chemical hypoxia selectively alters Ca2+ regulation in the growth cone and cell body of the same cell. 相似文献
146.
灌木状竹,有时附生于树干基部。地下茎短颈粗型。秆单丛;节问圆筒形;每节分枝单一,与主秆近等粗。秆释宿存性,革质;滓耳大,镰刀状;滓舌较低;算片外展。叶耳镰刀状; 相似文献
147.
Addi R. Fadel Dan Q. Jin Gaetano T. Montelione Ronald M. Levy 《Journal of biomolecular NMR》1995,6(2):221-226
Summary Order parameters for the backbone N–H and C–H bond vectors have been calculated from a 150 ps molecular dynamics (MD) simulation of human type- transforming growth factor in H2O solvent. Two kinds of crankshaft motions of the polypeptide backbone are observed in this MD trajectory. The first involves small-amplitude rocking of the rigid peptide bond due to correlated changes in the backbone dihedral angles i–1 and i. These high-frequency librational crankshaft motions are correlated with systematically smaller values of motional order parameters for backbone N–H bond vectors compared to C–H bond vectors. In addition, infrequent crankshaft flips of the peptide bond from one local minimum to another are observed for several amino acid residues. These MD simulations demonstrate that comparisons of N–H and C–H order parameters provide a useful approach for identifying crank-shaft librational motions in proteins. 相似文献
148.
Rasmus H. Fogh Dick Schipper Rolf Boelens Robert Kaptein 《Journal of biomolecular NMR》1995,5(3):259-270
Summary The 1H, 13C and 15N NMR resonances of serine protease PB92 have been assigned using 3D tripleresonance NMR techniques. With a molecular weight of 27 kDa (269 residues) this protein is one of the largest monomeric proteins assigned so far. The side-chain assignments were based mainly on 3D H(C)CH and 3D (H)CCH COSY and TOCSY experiments. The set of assignments encompasses all backbone carbonyl and CHn carbons, all amide (NH and NH2) nitrogens and 99.2% of the amide and CHn protons. The secondary structure and general topology appear to be identical to those found in the crystal structure of serine protease PB92 [Van der Laan et al. (1992) Protein Eng., 5, 405–411], as judged by chemical shift deviations from random coil values, NH exchange data and analysis of NOEs between backbone NH groups.Abbreviations 2D/3D/4D
two-/three-/four-dimensional
- HSQC
heteronuclear single-quantum coherence
- HMQC
heteronuclear multiple-quantum coherence
- COSY
correlation spectroscopy
- TOCSY
total correlation spectroscopy
- NOE
nuclear Overhauser enhancement (connectivity)
- NOESY
2D NOE spectroscopy
Experiment nomenclature (H(C)CH, etc.) follows the conventions used elsewhere [e.g. Ikura et al. (1990) Biochemistry, 29, 4659–4667]. 相似文献
149.
R. M. Valerio A. M. Bray N. J. Maeji P. O. Morgan J. W. Perich 《Letters in Peptide Science》1995,2(1):33-40
Summary The synthesis of two model Tyr(P)-containing peptides using Fmoc-Tyr(PO3
tBu2)-OH, Fmoc-Tyr(PO3Bzl2)-OH and Fmoc-Tyr(PO3H2)-OH established that the t-butylphosphate-protected derivative was the preferred derivative for use in Fmoc solid-phase peptide synthesis, since it afforded phosphopeptides in high purity and with the lowest amount of Tyr-peptide contamination. In addition, this study confirmed that commercially available Fmoc-Tyr(PO3H2)-OH is also suitable for use in Fmoc solid-phase synthesis but gives less pure phosphopeptides, along with the generation of 1–4% of the tyrosine-containing peptide for the model sequences studied. In view of the good performance of Fmoc-Tyr(PO3
tBu2)-OH, a large-scale three-step synthetic procedure was developed which involved phenacyl protection of the carboxyl group, phosphite-triester phosphorylation of the tyrosyl hydroxyl using di-t-butyl N,N-diethylphosphoramidite, and final removal of the phenacyl group by zinc reduction in acetic acid.Abbreviations BOP
benzotriazol-1-yl-oxy-tris(dimethylamino)phosphonium hexafluorophosphate
-
tBu
t-butyl
- Bzl
benzyl
- DBU
1,8-diazabicyclo[5,4,0]undec-7-ene
- DMF
N,N-dimethylformamide
- EDT
ethanedithiol
- Fmoc
9-fluorenylmethoxycarbonyl
- HOBt
N-hydroxybenzotriazole
- HPLC
high performance liquid chromatography
- NMM
N-methylmorpholine
- Pac
phenacyl
- TFA
trifluoroacetic acid
- THF
tetrahydrofuran
- Tyr(P)
O-phosphotyrosine 相似文献
150.
Marianne Borloo Koen Augustyns Alexander Belyaev Ingrid de Meester Anne-Marie Lambeir Filip Goossens Willy Bollaert Padinchare Rajan Simon Scharpé Achiel Haemers 《Letters in Peptide Science》1995,2(3-4):198-202
Summary A series of azaproline dipeptides with various N-substituents were synthesized as possible active-site-directed inhibitors of two proline-specific serine proteases, dipeptidyl peptidase IV and prolyl oligopeptidase. Compounds with semicarbazide, carbazate, acylhydrazine and sulphonylhydrazine structures were tested. Some compounds show moderate activity, i.e., in the millimolar range. 相似文献