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171.
A new compound, withangulatin A, promotes type II DNA topoisomerase-mediated DNA damage 总被引:1,自引:0,他引:1
J K Juang H W Huang C M Chen H J Liu 《Biochemical and biophysical research communications》1989,159(3):1128-1134
Withangulatin A, a new compound with a known chemical structure and from the antitumor Chinese herb Physalis angulata L, was found to act on topoisomerase II to induce topoisomerase II-mediated DNA damage in vitro. It has two effective dosage ranges of approximate 0.5 and 20 microM, with about one-third the activity of 20 microM VM-26. 相似文献
172.
Liver mitochondrial respiratory functions decline with age 总被引:14,自引:0,他引:14
T C Yen Y S Chen K L King S H Yeh Y H Wei 《Biochemical and biophysical research communications》1989,165(3):944-1003
Human liver mitochondrial respiration rates in Chinese populations of various ages were assayed with an oxygraph. In this study, State 3 and State 4 respiration rates, respiratory control ratio (RCR), and ADP/O ratio were measured for 35 Chinese subjects of 31 to 76 years old. We found a significant negative correlation between age and respiratory control and ADP/O ratios tested. Moreover, the respiratory control and ADP/O ratios decreased with the increase of age. These findings suggest that a substantial fall in mitochondrial oxidative capacity in ageing liver may be an important contributor to the ageing process. 相似文献
173.
D I Crane N H Chen C J Masters 《Biochemical and biophysical research communications》1989,160(2):503-508
Peroxisomal enoyl-CoA hydratase was purified from livers of mice treated with di-(2-ethylhexyl)phthalate and its properties compared with those of the 70 kDa protein present in the membranes prepared by carbonate extraction of peroxisomes. The two proteins had identical subunit molecular masses, of about 70,000 daltons. Limited proteolysis of these proteins using the V8 proteinase of S. aureus yielded identical peptide maps, with these peptides crossreacting with antiserum raised against the 70 kDa membrane protein. These data are consistent with the proposal that the peroxisomal 70 kDa membrane protein and the peroxisomal enoyl-CoA hydratase are the same protein. 相似文献
174.
We have examined the kinetics and mechanism by which iron can displace copper at the specific metal-binding sites of ovotransferrin. Fe2+ was added to Cu2+-ovotransferrin-CO3(2-) in the presence of NaHCO3 and ambient O2. The reaction has been followed by standard and stopped-flow spectrophotometry, EPR spectroscopy and analysis of chromogen-reactive Fe2+. The reaction is best described as triphasic. An initial jump in absorbance takes place in the first 2 s. In the next minute there is a further increase in absorbance and shift in the spectral maximum from 440 to 446 nm. The third phase is complex. The bulk of the spectrophotometric change, a decrease in absorbance with a shift to a maximum of 453 nm, lasts approx. 3 min. Minor spectral and EPR changes, however, take place over the next several hours. Chromogenic analysis of Fe2+ indicates that approx. 1 min is required to oxidize the Fe2+. EPR spectra reveal the formation of an Fe3+-ovotransferrin complex within the first 20 s; however, this lacks the characteristic doublet of specific Fe3+-ovotransferrin-CO3(2-). The simultaneous presence of specific Cu2+-ovotransferrin-CO3(2-) and Fe3+-ovotransferrin-CO3(2-) signals suggests a period in which the protein specifically binds both metal ions perhaps resulting from a differential reactivity of the two metal-binding sites. The addition of Cu(NO3)2 to Fe3+-ovotransferrin-CO3(2-) resulted in a complex with specific Fe3+ and non-specific Cu2+. The EPR spectrum of this complex and the final product of our displacement reaction were virtually identical. Distinct parallels in reaction of Cu2+-ovotransferrin-CO3(2-) with Fe(NH4)2(SO4)2, Fe(NO3)3 and Fe3+-nitrilotriacetic acid were observed. A reaction sequence involving the binding and oxidation of non-specific Fe2+ followed by Cu2+ displacement by Fe3+ at the specific sites and binding of non-specific Cu2+ is suggested. 相似文献
175.
G C Chen D A Hardman R L Hamilton C M Mendel J W Schilling S Zhu K Lau J S Wong J P Kane 《Biochemistry》1989,28(6):2477-2484
The distribution of lipid-binding regions of human apolipoprotein B-100 has been investigated by recombining proteolytic fragments of B-100 with lipids and characterizing the lipid-bound fragments by peptide mapping, amino acid sequencing, and immunoblotting. Fragments of B-100 were generated by digestion of low-density lipoproteins (LDL) in the presence of sodium decyl sulfate with either Staphylococcus aureus V8 protease, pancreatic elastase, or chymotrypsin. Particles with electron microscopic appearance of native lipoproteins formed spontaneously when detergent was removed by dialysis from enzyme digests containing fragments of B-100 and endogenous lipids, or from incubation mixtures of delipidated B-100 fragments mixed with microemulsions of exogenous lipids (cholesteryl oleate and egg phosphatidylcholine). Fractionation of the recombinant particles by isopycnic or density gradient ultracentrifugation yielded complexes similar to native LDL with respect to shape, diameter, electrophoretic mobility, and surface and core compositions. Circular dichroic spectra of these particles showed helicity similar to LDL but a somewhat decreased content of beta-structure. Most of the fragments of B-100 were capable of binding to lipids; 12 were identified by direct sequence analysis and 14 by reaction with antisera against specific sequences within B-100. Our results indicate that lipid-binding regions of B-100 are widely distributed within the protein molecule and that proteolytic fragments derived from B-100 can reassociate in vitro with lipids to form LDL-like particles. 相似文献
176.
Acquired immunity against Angiostrongylus cantonensis was induced by immunizing rats with somatic antigens from fifth-stage larvae and adult worms and live third-stage larvae. Rats immunized twice had significantly fewer worms than rats immunized three times. Fewer worms were recovered from rats immunized with 200 live third-stage larvae than from any other groups. Rats immunized with somatic antigens had higher enzyme-linked immunosorbent assay (ELISA) antibody levels than rats immunized with live larvae. Rats immunized with live third-stage larvae of Angiostrongylus cantonensis were more strongly protected against challenge infections (62-92%) than rats immunized with antigens extracted from fifth-stage larvae (0-30%) and adult worms (11-24%). 相似文献
177.
James M. Chen Grace Lee Paul W. Brandt-Rauf Randall B. Murphy Shalom Rackovsky Matthew R. Pincus 《Journal of Protein Chemistry》1990,9(5):543-547
The predicted conformation and position of the central transforming region (residues 55–67) of the p21 protein are compared with the conformation and position of this segment in a recently determined X-ray crystal structure of residues 1–166 of this protein in the activated state bound to a nonhydrolyzable GTP derivative. We previously predicted that this segment of the protein would adopt a roughly extended conformation from Ile 55-Thr 58, a reverse turn at Ala 59-Gln 61, followed by an -helix from Glu 62-Met 67. We further predicted that this region of the activated protein occupies a position that is virtually identical to corresponding regions in the homologous purine nucleotide-binding proteins, bacterial elongation factor (EF-tu), and adenylate kinase (ADK). We find that there is a close correspondence between the conformation and position of our predicted structure and those found in the X-ray crystal structure. A mechanism for activation of the protein is proposed and is corroborated by X-ray crystallographic data. 相似文献
178.
179.
180.
A 40 kilodalton rat liver nuclear protein binds specifically to apolipoprotein B mRNA around the RNA editing site. 总被引:8,自引:5,他引:3
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Apolipoprotein (apo) B-48 mRNA is the product of RNA editing which consists of a C----U conversion changing a CAA codon encoding Gln-2153 in apoB-100 mRNA to a UAA stop codon in apoB-48 mRNA. In the adult rat, RNA editing occurs both in the small intestine and the liver. We have studied the ability of rat liver nuclear extracts to bind to synthetic apoB mRNA segments spanning the editing site. Using an RNA gel mobility shift assay, we found the sequence-specific binding of a protein(s) to a 65-nucleotide apoB-100 mRNA. UV crosslinking followed by T1 ribonuclease digestion and SDS-polyacrylamide gel electrophoresis demonstrated the formation of a 40 kDa protein-RNA complex when 32P-labeled apoB-100 mRNA was incubated with a rat liver nuclear extract but not with HeLa nuclear extract. Binding was specific for the sense strand of apoB mRNA, and was not demonstrated with single-stranded apoB DNA, or antisense apoB RNA. The complex also failed to form if SDS was present during the UV light exposure. Binding experiments using synthetic apoB mRNAs indicate that the 40 kDa protein would also bind to apoB-48 mRNA but not apoA-I, apoA-IV, apoC-II or apoE mRNA. Experiments using deletion mutants of apoB-100 mRNA indicate efficient binding of wildtype 65-nucleotide (W65), 40-nucleotide (W40) and 26-nucleotide (W26) apoB-100 mRNA segments, but not 10-nucleotide (or smaller) segments of apoB-100 mRNA to the 40 kDa protein. In contrast, two other regions of apoB-100 mRNA, B-5' (bases 1128-3003) and B-3' (bases 11310-11390), failed to bind to the protein. The 40 kDa sequence-specific binding protein in rat liver nuclear extract may play a role in apoB-100 mRNA editing. 相似文献