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991.
铁氧还原白-NADP^+氧还酶(FNR)是光合电子传递中的关键酶之一。蓝细菌Synechococcus sp.PCC7002中编码FNR的petH基因被克隆到表达载体pET-3d上,在大肠杆菌中得到了高效表达,其表达量占大肠杆菌总蛋白的505%以上。高效表达的产物以可溶性和包含体两种形式存在。可溶性部分具有FNR的酶活性,在经过离子交换和凝胶层析后产生了电泳纯的FNR。包含体形式的部分经6.7mo 相似文献
992.
993.
Inherent or acquired resistance of tumor cells to cytotoxic drugs represents a major limitation to the successful chemotherapeutic
treatment of cancer. During the past three decades dramatic progress has been made in the understanding of the molecular basis
of this phenomenon. Analyses of drug-selected tumor cells which exhibit simultaneous resistance to structurally unrelated
anti-cancer drugs have led to the discovery of the human MDR1 gene product, P-glycoprotein, as one of the mechanisms responsible
for multidrug resistance. Overexpression of this 170 kDa N-glycosylated plasma membrane protein in mammalian cells has been
associated with ATP-dependent reduced drug accumulation, suggesting that P-glycoprotein may act as an energy-dependent drug
efflux pump. P-glycoprotein consists of two highly homologous halves each of which contains a transmembrane domain and an
ATP binding fold. This overall architecture is characteristic for members of the ATP-binding cassette or ABC superfamily of
transporters. Cell biological, molecular genetic and biochemical approaches have been used for structure-function studies
of P-glycoprotein and analysis of its mechanism of action. This review summarizes the current status of knowledge on the domain
organization, topology and higher order structure of P-glycoprotein, the location of drug- and ATP binding sites within P-glycoprotein,
its ATPase and drug transport activities, its possible functions as an ion channel, ATP channel and lipid transporter, its
potential role in cholesterol biosynthesis, and the effects of phosphorylation on P-glycoprotein activity.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
994.
Targeting of chloroplast proteins to the thylakoid membrane is analogous to bacterial secretion, and much of what we know has been learned from secretory mechanisms in Escherichia coli. However, chloroplasts also use a ΔpH-dependent pathway to target thylakoid proteins, at least some of which are folded before transport. Previously, this pathway seemed to have no cognate in bacteria, but recent results have shown that the HCF106 gene in maize encodes a component of this pathway and has bacterial homologues. This ΔpH-dependent pathway might be an ancient conserved mechanism for protein translocation that evolved before the endosymbiotic origin of plastids and mitochondria. 相似文献
995.
Tak Yee Aw 《Free radical research》1998,28(6):637-646
It has long been recognized that hydroperoxides are agents of cytotoxicity. However, in recent years, it is increasingly apparent that lipid hydroperoxide may play an important role in mediating cellular and molecular events in degenerative pathophysiological processes that lead to intestinal disorders, such as cancer. Yet, surprisingly, little is known of the intestinal disposition of peroxidized lipids and of the metabolic factors that determine mucosal peroxide elimination. The present paper summarizes the evidence for the pivotal role of reductant (GSH and NADPH) availability in intestinal peroxide detoxication. This information will provide important insights into the relationship between luminal lipid hydroperoxides and intestinal GSH redox homeostasis, and is pertinent to understanding how dietary oxidants like lipid peroxides, can impact intestinal integrity with implications for genesis of gut pathology. 相似文献
996.
The exact timing ofAnguilla japonica spawning was determined from analyses of daily otolith increments in leptocephali collected near a spawning area west of
the Mariana Islands on July 1–18, 1991. The birth dates of the 54 leptocephali examined (10.2 to 30.5 mm in total length)
ranged from May 22 to June 24, 1991, the individuals clearly comprising two age groups, May-born fish (mode May 28) and June-born
fish (mode June 21). The data showed thatA. japonica spawns intermittently during the spawning season, with fixed synchronized timing. Each group of leptocephali collected along
three different north-south transects (131°, 134° and 137°E between 10° and 22°N) comprised both May-born and June-born fish.
The latter were dominant along the easternmost and middle transects, whereas the May-born fish were more abundant along the
westernmost transect. The modal ages of the June-born and May-born fish collected along 137°E on July 1–3 were 13 d and 35
d, respectively, while those of the two age groups collected along 134°E on July 17 and 18 were 28 d and 50 d, respectively.
These data show that the interval between the sampling dates for the two transects (ca. 15 d) corresponded closely to the
differences in modal ages of specimens from the two transects (15 d) for both the May- and June-born fish, and further, that
the difference in modal age between the two age groups (22 d) was the same at both transects. A similar correspondence in
total length was also observed between the two age groups at the above two transects. The findings clearly demonstrated parallel
westward transport by the North Equatorial Current for both the May- and June-born eel leptocephali, which originated from
a spawning area estimated as being between 141° and 143°E. 相似文献
997.
Kruk Jerzy Burda Kveta Schmid Georg H. Radunz Alfons Strzałka Kazimierz 《Photosynthesis research》1998,58(2):203-209
We have found that in petroleum-ether extracted tobacco thylakoids, plastoquinone A (PQ-A) and plastoquinone C (PQ-C) had similar efficiency in restoration of oxygen-evolving activity, while plastoquinone B (PQ-B), which is a fatty acid ester of PQ-C, was about 50% less effective. This indicates that apart from PQ-A, PQ-C and to a smaller extent PQ-B may function as electron acceptors of Photosystem II (PS II). The DCMU inhibition curves for PQ-C and PQ-B were biphasic and an initial slow decline was followed by a sharp decrease in oxygen evolution yield with a 50% inhibition (I50) at 0.25 M DCMU. In the case of PQ-A (I50 = 0.20 M DCMU), the activity decreased gradually without the sharp transition. The corresponding inhibition curve for unextracted thylakoids, where all the native prenylquinones are present, shows an intermediate shape between PQ-A and PQ-C but with a higher I50, equal to 0.32 M, suggesting that the contribution of PQ-C as an electron acceptor of Photosystem II might be significant in thylakoid membranes with natural prenyllipid composition. -Tocopherol quinone showed no activity in the restoration of oxygen evolution in extracted thylakoids, indicating that it cannot accept electrons from PS II. The fatty acid composition of PQ-B isolated from maple leaves showed a high degree of saturated fatty acids like myristic and palmitic acid, and its unique composition indicates that it is a natural component of the thylakoid membrane. 相似文献
998.
John W. Chandler 《BioEssays : news and reviews in molecular, cellular and developmental biology》2009,31(1):60-70
Auxin is a plant growth regulator involved in diverse fundamental developmental responses. Much is now known about auxin transport, via influx and efflux carriers, and about auxin perception and its role in gene regulation. Many developmental processes are dependent on peaks of auxin concentration and, to date, attention has been directed at the role of polar auxin transport in generating and maintaining auxin gradients. However, surprisingly little attention has focussed on the role and significance of auxin biosynthesis, which should be expected to contribute to active auxin pools. Recent reports on the function of the YUCCA flavin monooxygenases and a tryptophan aminotransferase in Arabidopsis have caused us to look again at the importance of local biosynthesis in developmental processes. Many alternative and redundant pathways of auxin synthesis exist in many plants and it is emerging that they may function in response to environmental cues. 相似文献
999.
1000.
Gaspar E. Canepa León A. Bouvier Mariana R. Miranda Antonio D. Uttaro & Claudio A. Pereira 《FEMS microbiology letters》2009,292(1):27-32
l -Cysteine and methionine are unique amino acids that act as sulfur donors in all organisms. In the specific case of Trypanosomatids, l -cysteine is particularly relevant as a substrate in the synthesis of trypanothione. Although it can be synthesized de novo , l -cysteine is actively transported in Trypanosoma cruzi epimastigote cells. l -Cysteine uptake is highly specific; none of the amino acids assayed yield significant differences in terms of transport rates. l -Cysteine is transported by epimastigote cells with a calculated apparent K m of 49.5 μM and a V max of about 13 pmol min−1 per 107 cells. This transport is finely regulated by amino acid starvation, extracellular pH, and between the parasite growth phases. In addition, l -cysteine is incorporated post-translationally into proteins, suggesting its role in iron–sulfur core formation. Finally, the metabolic fates of l -cysteine were predicted in silico . 相似文献