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71.
Intact sediment cores were obtained from three New York lakes in May, July, and October 1981. Radioactive S (as 35SO
4
2−
) was added to the overlying water and cores were incubated without atmospheric exchange for one week near lake bottom temperatures.
Headspace flux of 02 as an index of sediment respiration rates varied among lakes and seasonally within lakes. Acidic South Lake had the lowest
respiration rate at all seasons and also the smallest net incorporation of the 35SO
4
2−
. Summer net isotope transformation into ester sulfate and non-HI reducible S (pyrite and C-bonded S) constituents was 88.6%,
89.4%, and 59.7% of total sediment isotope for Oneida, Deer, and South, respectively. Seasonal variation of net isotope incorporation
was observed in each lake as were differences in 35SO
4
2−
partitioning into major S pools. Of the S constituents analyzed, HCl digestible S (volatile sulfides) was the smallest pool,
while ester sulfate and non-HI reducible S together accounted for greater than 50% of S isotope transformation in all lakes.
In addition, ester sulfate is the major product of dissolved SO
4
2−
transformation and its formation results in less alkalinity generation than the formation of non-HI reducible S constituents.
Thus ester sulfate transformation processes must be considered in calculating alkalinity generation by lake sediments.
Financial support provided by Office of Water Research Technology (Project No. 13-096-NY).
Financial support provided by Office of Water Research Technology (Project No. 13-096-NY). 相似文献
72.
Phosphatases; origin,characteristics and function in lakes 总被引:14,自引:4,他引:14
Phosphatases catalyze the liberation of orthophosphate from organic phosphorus compounds. The total phosphatase activity in lake water results from a mixture of phosphatases localized on the cell surfaces of algae and bacteria and from dissolved enzymes supplied by autolysis or excretion from algae, bacteria and zooplankton. External lake water phosphatases usually have pH optima in the alkaline region. Acid phosphatases generally seem to be active in the internal cell metabolism. The synthesis of external alkaline phosphatases is often repressed at high phosphate concentrations and derepressed at low phosphate concentrations. Phosphatase activity has therefore been used as a phosphorus deficiency indicator in algae and in natural plankton populations. The possibilities for this interpretation of phosphatase activity in lake water are limited, however, and this is discussed. The in situ hydrolysis capacity, i.e. the rate by which orthophosphate is released from natural substrates, is unknown. However, we advocate that this process is important and that the rate of substrate supply, rather than phosphatase activity, limits the enzymatic phosphate regeneration. 相似文献
73.
Phenyl di-n-pentylphosphinate is a reasonably stable easily synthesized inhibitor of neuropathy target esterase (NTE) with low anticholinesterase activity. Like phenylmethylsulphonyl fluoride it protects hens against neuropathic effects of compounds such as diisopropylphosphorofluoridate. At intervals up to 15 days after dosing hens (10 mg/kg s.c. to inhibit 90% NTE) assays were made of catalytically active and of phosphinylated NTE in autopsy tissue. The sum of these components was always within the range of catalytic activity in undosed controls. However, the half-life of reappearance of active NTE was 2.07 days +/- 0.13 (SD, n = 6) for brain and 3.62 days +/- 0.23 (SD, n = 6) for spinal cord--shorter than after dosing with phenylmethylsulphonyl fluoride. It is proposed that: (1) The physiological turnover mechanism cannot distinguish between catalytically active and di-n-pentylphosphinylated NTE although initiation of organophosphate-induced delayed polyneuropathy might involve recognition of aged di-alkyl-phosphorylated NTE as "foreign". (2) The short half-lives indicate a slow spontaneous dephosphinylation of inhibited NTE occurs in vivo as well as de novo synthesis. The difference in half-lives for brain and spinal cord NTE may be due to different rates of synthesis de novo or (more likely) to different rates of spontaneous reactivation of the inhibited NTE in the two tissues. 相似文献
74.
Sj?gren-Larsson syndrome (SLS) is an inherited neurocutaneous disorder characterized by ichthyosis, mental retardation, spasticity, and deficient activity of fatty aldehyde dehydrogenase (FALDH). FALDH is an enzyme component of fatty alcohol:NAD oxidoreductase (FAO), which is necessary for fatty alcohol metabolism. To better understand the biochemical basis for the cutaneous symptoms in this disease, we investigated lipid metabolism in cultured keratinocytes from SLS patients. Enzyme activities of FALDH and FAO in SLS cells were <10% of normal. SLS keratinocytes accumulated 45-fold more fatty alcohol (hexadecanol, octadecanol, and octadecenol) than normal, whereas wax esters and 1-O-alkyl-2,3-diacylglycerols were increased by 5.6-fold and 7.5-fold, respectively. SLS keratinocytes showed a reduced incorporation of radioactive octadecanol into fatty acid (24% of normal) and triglyceride (13% of normal), but incorporation into wax esters and 1-O-alkyl-2,3-diacylglycerol was increased by 2.5-fold and 2.8-fold, respectively. Our results indicate that FALDH deficiency in SLS keratinocytes causes the accumulation and diversion of fatty alcohol into alternative biosynthetic pathways. The striking lipid abnormalities in cultured SLS keratinocytes are distinct from those seen in fibroblasts and may be related to the stratum corneum dysfunction and ichthyosis in SLS. 相似文献
75.
Omeje Edwin Ogechukwu Osadebe Patience Ogoamaka Nworu Chukwuemeka Sylvester Amal Hassan Abdessamad Debbab Esimone Charles Okechukwu Akira Kawamura Proksch Peter 《Phytochemistry letters》2011,4(3):357-362
In search of immunomodulatory constituents from the Eastern Nigeria mistletoe, Loranthus micranthus Linn, two new stigmastane steroids: stigmast-7,20 (21)-diene-3β-hydroxy-6-one (1) and 3β-hydroxy-stigmast-23-ene (2); three (two new and one known) lupeol-based triterpenoid esters: 7β,15α-dihydroxyl-lup-20(29)-ene-3β-palmitate (3), 7β,15α-dihydroxyl-lup-20(29)-ene-3β-stearate (4) and 7β,15α-dihydroxyl-lup-20(29)-ene-3β-eicosanoate (5) were isolated and characterized following bioactivity-guided fractionation. The new compounds, 1, 2, 4 and 5 at concentrations of 10, 25 and 100 μg/ml were subjected to cell proliferation and early activation marker (CD69) expression studies in C57Bl/6 mice splenocytes using flow cytometry techniques against Lipopolysaccharide (LPS; 10 μg/ml) and Concanavalin A (ConA; 2 μg/ml) standards. The stigmastane steroids (1 and 2) at the highest concentration of 100 μg/ml showed statistically significantly (p < 0.05) stimulatory activity on the C57B1/6 splenocytes compared to the controls with values of 46 ± 0.76% and 43 ± 0.46% compared to 7.69 ± 0.41% recorded for the negative control. The novel lupeol esters, 4 and 5 at same concentration of 100 μg/ml exhibited lower stimulations of 30 ± 0.41% and 29 ± 0.17% respectively compared to the controls above. The CD69 expression assay at the above doses showed that all the compounds have minimal stimulation. The present study supports the observed immunomodulatory property of the Eastern Nigeria mistletoe and thus confirms the efficacy of this plant in mitigating against wide array of disease conditions orchestrated by immunodeficiency. 相似文献
76.
以羰基二咪唑为催化剂,生物素与6-氨基己酸甲酯反应生成生物素-6-氨基己酸甲酯,该化合物通过酸碱萃取与原料分离,皂化后生成生物素氨基己酸.生物素氨基己酸在吡啶存在下与三氟乙酸对硝基苯酯进行转酯反应即得生物素对硝基苯酯.最后经光谱、色谱及核酸杂交证实了长臂生物素对硝基苯酯的化学结构和生物学活性. 相似文献
77.
蛋白激酶C在血小板聚集中的作用 总被引:4,自引:0,他引:4
利用 ̄(32)P-NaH2PO4标记猪血小板,以蛋白激酶C的40kD底物为蛋白激活的标志.用血小板激动剂在聚集浓度范围内处理血小板,结果表明,除了不能使猪血小板聚集的肾上腺素外,凝血酶等激动剂都使血小板40kD底物蛋白磷酸化明显增加,同时38kD,26kD蛋白质磷酸化也明显增加,且40kD底物磷酸化与血小板聚集有平行增加关系.蛋白激酶C在血小板聚集中可能起着重要的调节作用。 相似文献
78.
Toshifumi Miyazawa Makoto Hiramatsu Takashi Murashima Takashi Yamada 《Biotechnology letters》2002,24(23):1945-1949
The coupling between the carbamoylmethyl ester of an N-protected amino acid or dipeptide (at 25 mM) and an amino acid amide (at 100 mM) was achieved using Aspergillus melleus protease in 1,1,1,3,3,3-hexafluoro-2-propanol/N,N-dimethylformamide (1:1, v/v); the coupling efficiencies were dependent largely on the combination of amino acid residues: e.g. the dipeptide yields after 48 h were for l-Ala + Gly, 100% and for l-Leu + l-Leu, 16%. 相似文献
79.
Manh Huynh Vu Tetsu Ando Shigeo Yoshida Nobutaka Takahashi Sadahiro Tatsuki Kazumasa Katagiri 《Bioscience, biotechnology, and biochemistry》2013,77(7):1615-1617
Ferredoxin-nitrite reductase (EC 1.7.7.1), an enzyme which catalyzes the 6-electron reduction of nitrite to ammonia, has been isolated from Spinacia oleracea. The isolated enzyme was homogeneous by disc electrophoresis with polyacrylamide gel. The molecular weight of the enzyme was estimated to be 86,000 by Ultrogel AcA 34 gel filtration. In the oxidized form, the enzyme had absorption maxima at 278, 388 (Soret band), 573 (α band) and 690 nm, indicating that siroheme is directly involved in the catalysis of nitrite reduction. This absorption spectrum was modified by sulfite, hydroxylamine and cyanide. The enzyme exhibited electron paramagnetic resonance signals with g values of 6.9 and 5.2, which are characteristic of a high spin Fe3+ -siroheme in the molecule. These signals disappeared upon the addition of dithionite or nitrite. This isolated enzyme also contained four moles of labile sulfide and 7 g-atoms of iron per 86,000 g of protein. 相似文献
80.
Air-dried cells of Hansenula nonfermentans AKU 4332 catalyzed the production of (S)-3-pentyn-2-ol from (RS)-3- pentyn-2-ol acetate ester at 10% (v/v). The product was formed at 96.6% e.e. with a molar yield of 45% in 24 h. © Rapid Science Ltd. 1998 相似文献