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41.
42.
Under very mild oxidizing conditions the delta subunit of the F1-ATPase of Escherichia coli can be crosslinked by a disulfide linkage to one of the alpha subunits of the enzyme. The cross-linked ATPase resembles the native enzyme in the following properties: specific activity; activation by lauryldimethylamine N-oxide (LDAO); binding of aurovertin D and ADP; cross-linking products with 3,3'-dithiobis(succinimidyl propionate); binding to ATPase-stripped everted membrane vesicles and the N,N'-dicyclohexylcarbodiimide sensitivity of the rebound enzyme. However, the rebound crosslinked ATPase differed from the native enzyme in lacking the ability to restore NADH oxidation - and ATP hydrolysis-dependent quenching of the fluorescence of quinacrine to ATPase-stripped membrane vesicles. It is proposed that the delta subunit is involved in the proton pathway of the ATPase, and that this pathway is affected in the alpha delta-cross-linked enzyme. The mechanism for activation of the ATPase by LDAO was examined. Evidence against the proposal of L?tscher, H.-R., De Jong, C. and Capaldi, R.A. (Biochemistry (1984) 23, 4140-4143) that activation involves displacement of the epsilon subunit from an active site on a beta subunit was obtained. 相似文献
43.
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45.
The effects of positively charged nylon and depth (cellulose-diatomaceous earth) filters on endotoxin removal from various solutions were evaluated. The charged filter media removed significant amounts of Escherichia coli and natural endotoxin from tap water, distilled water, sugars, and NaCl solutions; no significant removal of endotoxin was observed with negatively charged filter media. The extent of removal was influenced by pH, the presence of salts, and organic matter. Such media may be useful for the control of endotoxins in raw-product water or solutions used to prepare parenteral drug products or in other fluids where endotoxin control is desired. 相似文献
46.
S W Melanson C H Yun M L Pezzementi L Pezzementi 《Comp. Biochem. Physiol. C, Comp. Pharmacol. Toxicol.》1985,81(1):87-96
The acetylcholinesterase activity of the fruit fly, Drosophila melanogaster, was characterized biochemically. The activity is associated with a glycoprotein which is divided between a detergent-extractable membrane-bound fraction and a soluble fraction. The acetylcholinesterase activity is concentrated in the head of the insect. Through pharmacological methods, greater than 95% of the cholinesterase is judged to be true acetylcholinesterase, and not pseudocholinesterase. As expected for an acetylcholinesterase, the enzyme has a high affinity for acetylthiocholine and is inhibited by excess concentrations of acetylthiocholine. The soluble enzyme is found predominantly as a 7.8 S form; a smaller amount of an approximately 6 S form is also present, and a greater than or equal to 14 S form may exist. The detergent-solubilized acetylcholinesterase has a sedimentation coefficient of 7.5 S in the presence of detergent. The thermal inactivation rates for the soluble and the membrane bound enzymes are markedly different. 相似文献
47.
银杏科研的主要成就和展望 总被引:4,自引:0,他引:4
前言银杏又名白果,是现存种子植物中最古老的孑遗植物,也是源于我国的特有珍贵树种。学者们一向把它视为植物界的奇珍,在植物分类学、树木学、果树栽培学和古植物学上占有特殊的位置,至今国内外植物学家、地质学家,以及果树栽培学家们,仍对它进行着深入细致的研究。银杏的科学奥秘将逐步被揭开。 相似文献
48.
Immature rats (aged 28 days) were injected with 4, 20, or 40 IU pregnant mare serum gonadotropin (PMSG) and sacrificed every 6 or 12 hr. Control rats (4 IU) ovulated between 60 and 72 hr, whereas rats given superovulatory doses of PMSG (20 and 40 IU) ovulated between 24 and 72 hr. The oocyte count from the superovulated rats increased slightly between 24 and 36 hr and markedly between 48 and 72 hr. Degenerated oocytes were recovered 48 and 36 hr after administration of 20 and 40 IU PMSG, respectively. Thereafter, the proportion of degenerated oocytes was dose dependent and reached a maximum at 72 (30.9%, 20 IU) and 60 hr (61.0%, 40 IU). 17β-estradiol content of the superovulated ovaries increased significantly (P < 0.01) from 36 hr and was maximal at 60 (20 IU) or 54 hr (40 IU), when compared to the control regimen. Administration of 40 IU PMSG resulted in a biphasic increase of progesterone content with the peaks at 36 and 60 hr. Androgen content of the superovulated ovaries was lower than control levels during the first 36 hr but was significantly (P < 0.01) higher thereafter. The results suggest that these alterations in the steroid response (particularly androgens) from 36 hr onward following superovulation may be responsible for the coincidental occurrence of abnormal oocytes, possibly by disturbing the specific intrafollicular steroid environment essential for complete maturation. In addition, oocyte aging that is due to earlier activation by the exogenous luteinizing hormone activity may be a contributing factor. 相似文献
49.
Jan Kopecký Josef Houštěk Eva Szarska Zdeněk Drahota 《Journal of bioenergetics and biomembranes》1986,18(6):507-519
The proteolipid subunit of H+-ATPase was labeled by [14C]N,N-dicyclohexylcarbodiimide in bovine heart mitochondria. The radioactive labeling was followed using various systems of sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE). When using discontinuous SDS-PAGE (Laemmli, U.K., 1970,Nature (London)227, 680–685) a monomeric (Mr 7600±1500) and a dimeric form (Mr 17,800±1200) of the proteolipid were detected, while only the monomeric form was found on urea (8 M) containing gels (SDS-PAGE according to Laemmli; or Swank, R. T., and Munkers, K. D., 1971,Anal. Biochem.
39, 462–477). When using SDS-PAGE with Na-Pi buffer (Weber, K., and Osborn, M., 1969,J. Biol. Chem.
244, 4406–4442), only a dimeric form of the proteolipid (Mr 15,000±1000) was detected. Experimental data indicate that the different patterns of proteolipid separation are related to the presence of the two distinct proteolipid conformations in the SDS solution. 相似文献
50.
Ramesh N. Patel Ching T. Hou P. Derelanko 《Archives of biochemistry and biophysics》1983,221(1):135-142
An NAD+-linked, reduced glutathione-dependent formaldehyde dehydrogenase was purified to homogeneity from soluble extracts of methanol-grown yeast, Pichia sp. Formaldehyde and methylglyoxal are oxidized in the presence of NAD+ as an electron acceptor. NADP+ could not replace NAD+. Other straight chain aldehydes (C2–C6 tested), branched-chain aldehydes (e.g., isobutyaldehyde), aromatic aldehydes (e.g., salicylal-dehyde, benzaldehyde), glutyraldehyde, glyceraldehyde, glycoaldehyde, and glyoxal-dehyde tested were not oxidized by the purified formaldehyde dehydrogenase. The product of formaldehyde oxidation by purified enzyme was demonstrated to be S-for-mylglutathione by measuring the absorption at 240 nm due to the formation of thioester of formaldehyde and reduced glutathione. The Km values for NAD+, formaldehyde, and reduced glutathione were 0.12, 0.31, and 0.16 mm, respectively, for the forward reaction at pH 8.0. The purified formaldehyde dehydrogenase also catalyzed the reduction of S-formylglutathione in the presence of NADH. Formate was not reduced by the purified enzyme. The Km values for S-formylglutathione and NADH were 0.60 and 0.25 mm, respectively, for the reverse reaction at pH 6.0. Formaldehyde dehydrogenase has a molecular weight of 84,000 as determined by gel filtration and subunit molecular weight of 41,000 as determined by sodium dodecyl sulfate-gel electrophoresis. S-Formylglutathione, a product of formaldehyde oxidation, was oxidized by the partially purified formate dehydrogenase from Pichia sp. Formate dehydrogenase has a higher affinity toward S-formylglutathione (Km value 1.8 mm) than toward formate (Km value 25 mm). Antiserum prepared against the purified formaldehyde dehydrogenase from Pichia sp. NRRL-Y-11328 forms strong precipitin bands with isofunctional enzymes from methanol-grown Pichia pastoris NRRL-Y-7556 and Torulopsis candida Y-11419 and weak precipitin bands with Hansenula polymorpha NRRL-Y-2214. No cross-reaction was observed with isofunctional enzyme derived from methanol-grown Kloeckera sp. 相似文献