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71.
The ability of particular cell surface glycoproteins to recycle and become
exposed to individual Golgi enzymes has been demonstrated. This study was
designed to determine whether endocytic trafficking includes significant
reentry into the overall oligosaccharide processing pathway. The Lec1
mutant of Chinese hamster ovary (CHO) cells lack N -
acetylglucosaminyltransferase I (GlcNAc-TI) activity resulting in surface
expression of incompletely processed Man5GlcNAc2 N -linked
oligosaccharides. An oligosaccharide tracer was created by exoglycosylation
of cell surface glycoproteins with purified porcine GlcNAc-TI and
UDP-[3H]GlcNAc. Upon reculturing, all cell surface glycoproteins that
acquired [3H]GlcNAc were acted upon by intracellular mannosidase II, the
next enzyme in the Golgi processing pathway of complex N -linked
oligosaccharides (t1/2= 3-4 h). That all radiolabeled cell surface
glycoproteins were included in this endocytic pathway indicates a common
intracellular compartment into which endocytosed cell surface glycoproteins
return. Significantly, no evidence was found for continued oligosaccharide
processing consistent with transit through the latter cisternae of the
Golgi apparatus. These data indicate that, although recycling plasma
membrane glycoproteins can be reexposed to individual Golgi-derived
enzymes, significant reentry into the overall contiguous processing pathway
is not evident.
相似文献
72.
Corn samples were collected in 1999 from three departments of Entre Réos province, Argentina, and were surveyed for mould
contamination and natural occurrence ofFusarium mycotoxins, ochratoxin A and aflatoxins.Fusarium verticillioides was the most prevalent fungal species recorded at all departments. Zearalenone, deoxynivalenol and ochratoxin A were not
found in any samples. Only one of the 52 corn samples analysed was contaminated with aflatoxin B1 (17 μg/kg). Fumonisin B1 was found in 58 % of samples (range of positive samples: 47– 3,347 μg/kg), fumonisin B2 in 33.0 % (range of positive samples: 23–537 μg/kg) and fumonisin B3 in 25.0 % (range of positive samples: 24–287 μg/kg) of them. This is the first report on the natural occurrence of mycotoxins
in corn from Entre Ríos province, Argentina. Levels of fumonisins were lower than detected in other Argentinian provinces. 相似文献
73.
74.
Despite the recent introduction of biological response modifiers and potent new small-molecule antirheumatic drugs, the efficacy of methotrexate is nearly unsurpassed in the treatment of inflammatory arthritis. Although methotrexate was first introduced as an antiproliferative agent that inhibits the synthesis of purines and pyrimidines for the therapy of malignancies, it is now clear that many of the anti-inflammatory effects of methotrexate are mediated by adenosine. This nucleoside, acting at one or more of its receptors, is a potent endogenous anti-inflammatory mediator. In confirmation of this mechanism of action, recent studies in both animals and patients suggest that adenosine-receptor antagonists, among which is caffeine, reverse or prevent the anti-inflammatory effects of methotrexate. 相似文献
75.
Hsiao-Fen Li Chia-Hsuan Huang Li-Shuang Ai Chin-Kai Chuang Steve SL Chen 《Journal of biomedical science》2009,16(1):89-18
Background
Envelope (E) glycoprotein E2 of the hepatitis C virus (HCV) mediates binding of the virus to target cell receptors. Nevertheless, the precise role of E1 in viral entry remains elusive. 相似文献76.
Twenty-three V. parahaemolyticus strains, including 12 pandemic O3:K6 strains, were examined for their growth and production of thermostable direct hemolysin
(TDH) under an anaerobic culture condition with or without presence of a bile acid, taurocholic acid (TCA). Both bacterial
growth and TDH production were markedly enhanced by TCA for a majority of the strains, but the scale of the TDH production
was disproportionately greater than that of the corresponding growth for 14 strains. Such enhancement was, however, not specific
to the pandemic strains.
Received: 27 August 2001 / Accepted: 15 October 2001 相似文献
77.
The role of site-specific N-glycosylation in secretion of soluble forms of rabies virus glycoprotein 总被引:1,自引:1,他引:0
Wojczyk BS; Stwora-Wojczyk M; Shakin-Eshleman S; Wunner WH; Spitalnik SL 《Glycobiology》1998,8(2):121-130
Rabies virus glycoprotein is important in the biology and pathogenesis of
neurotropic rabies virus infection. This transmembrane glycoprotein is the
only viral protein on the surface of virus particles, is the viral
attachment protein that facilitates virus uptake by the infected cell, and
is the target of the host humoral immune response to infection. The
extracellular domain of this glycoprotein has N- glycosylation sequons at
Asn37, Asn247, and Asn319. Appropriate glycosylation of these sequons is
important in the expression of the glycoprotein. Soluble forms of rabies
virus glycoprotein were constructed by insertion of a stop codon just
external to the transmembrane domain. Using site-directed mutagenesis and
expression in transfected eukaryotic cells, it was possible to compare the
effects of site-specific glycosylation on the cell-surface expression and
secretion of transmembrane and soluble forms, respectively, of the same
glycoprotein. These studies yielded the surprising finding that although
any of the three sequons permitted cell surface expression of full-length
rabies virus glycoprotein, only the N-glycan at Asn319 permitted secretion
of soluble rabies virus glycoprotein. Despite its biological and medical
importance, it has not yet been possible to determine the crystal structure
of the full-length transmembrane form of rabies virus glycoprotein which
contains heterogeneous oligosaccharides. The current studies demonstrate
that a soluble form of rabies virus glycoprotein containing only one sequon
at Asn319 is efficiently secreted in the presence of the N-glycan
processing inhibitor 1-deoxymannojirimycin. Thus, it is possible to purify
a conformationally relevant form of rabies virus glycoprotein that contains
only one N-glycan with a substantial reduction in its microheterogeneity.
This form of the glycoprotein may be particularly useful for future studies
aimed at elucidating the three-dimensional structure of this important
glycoprotein.
相似文献
78.
Occurrence of urease-positive Vibrio parahaemolyticus in Kanagawa, Japan, with specific reference to presence of thermostable direct hemolysin (TDH) and the TDH-related-hemolysin genes. 总被引:5,自引:1,他引:4 下载免费PDF全文
A total of 132 strains of V. parahaemolyticus isolated from patients and from the suspected causal food items of past food poisoning cases occurring in Kanagawa Prefecture, Japan, were examined for the ability to hydrolyze urea, with specific reference to the presence of the thermostable direct hemolysin gene (tdh) and the gene for thermostable direct hemolysin-related hemolysin (trh). Ten strains belonging to five different O-antigen serotypes were positive for urea hydrolysis (UH+), and four of these strains did not carry tdh. A total of 106 strains carried tdh, but less than 6% of them were UH+, whereas all trh-carrying strains were UH+. The evidence suggests that urea hydrolysis is not a reliable marker for identifying tdh-carrying V. parahaemolyticus strains in Japan (the Pacific Northeast) but may be a marker for trh-carrying strains. 相似文献
79.
80.
Yoshihisa Hirota Naoko Tsugawa Kimie Nakagawa Yoshitomo Suhara Kiyoshi Tanaka Yuri Uchino Atsuko Takeuchi Natsumi Sawada Maya Kamao Akimori Wada Takashi Okitsu Toshio Okano 《The Journal of biological chemistry》2013,288(46):33071-33080
Mice have the ability to convert dietary phylloquinone (vitamin K1) into menaquinone-4 (vitamin K2) and store the latter in tissues. A prenyltransferase enzyme, UbiA prenyltransferase domain-containing 1 (UBIAD1), is involved in this conversion. There is evidence that UBIAD1 has a weak side chain cleavage activity for phylloquinone but a strong prenylation activity for menadione (vitamin K3), which has long been postulated as an intermediate in this conversion. Further evidence indicates that when intravenously administered in mice phylloquinone can enter into tissues but is not converted further to menaquinone-4. These findings raise the question whether phylloquinone is absorbed and delivered to tissues in its original form and converted to menaquinone-4 or whether it is converted to menadione in the intestine followed by delivery of menadione to tissues and subsequent conversion to menaquinone-4. To answer this question, we conducted cannulation experiments using stable isotope tracer technology in rats. We confirmed that the second pathway is correct on the basis of structural assignments and measurements of phylloquinone-derived menadione using high resolution MS analysis and a bioassay using recombinant UBIAD1 protein. Furthermore, high resolution MS and 1H NMR analyses of the product generated from the incubation of menadione with recombinant UBIAD1 revealed that the hydroquinone, but not the quinone form of menadione, was an intermediate of the conversion. Taken together, these results provide unequivocal evidence that menadione is a catabolic product of oral phylloquinone and a major source of tissue menaquinone-4. 相似文献