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Biomedical subjects

Y Tu

Publications and source records attributed to Y Tu.

162 records · Page 9Linked to original sources
PubMed1984

Preliminary crystallographic studies on bacterioferritin from Azotobacter vinelandii.

Bacterioferritin-cytochrome from Azotobacter vinelandii is an unusual protein containing haem groups as well as iron core like other ferritin. This paper reports the purification of bacterioferritin by affinity chromatography and the formation of brick-red crystals from a solution containing MgCl2. The crystals are optical isotropic with maximum dimensions of 0.4 X 0.4 X 0.1 mm3. The preliminary X-ray crystallographic studies have been performed. 1.5 degrees unscreened precession photographs show that the crystals of bacterioferritin belong to the cubic system, space group I432, with cell dimension 230 A. There are probably 8 molecules in one cubic unit cell and the molecule might have 32 symmetry. A molecular diameter of 115 A is derived from the packing of the molecules and a molecular weight of 826,000 is estimated for bacterioferritin.

Azotobacter↗
PubMed1980

Presence of a cytochrome b-containing ferritin in Azotobacter vinelandii.

It has been demonstrated that a cytochrome b-containing ferritin is present in Azotobacter vinelandii. After DEAE cellulose chromatography and purification fractional precipitation by 50% of the saturated ammonium sulfate of the extract prepared from A. vinelandii cells, a hexagonal crystalline preparation is obtained. The protein contains 4--6% of nonheme iron. The protein molecule is made up of an electron dense iron core with a diameter of 70A and a protein shell with a diameter of 120A. The Fe core can be removed from the shell by the treatment with chelating and reducing agents. Electron micrographs and absorption spectra reveal that the protein shells are very similar before and after the removal of the core. The electrophoretic mobility and immunological properties of the Fe-free protein against the antibody of ferritin are very similar to those of the protein before the removal of the iron. From the above characteristics, it can be inferred that the protein belongs to ferritin. The protein part contains protoheme as prosthetic group and so it belongs to cytochrome b. Hence, the protein prepared from A. vinelandii is a kind of cytochrome b-containing ferritins. The possible role of the ferritin in biological nitrogen fixation is discussed in this paper.

Apoferritins↗
PubMed1976

Effect of nitrofurazone on bacterial RNA and ribosome synthesis and on the function of ribosomes.

Exposure of E. coli B/r to nitrofurazone strongly inhibits the synthesis of all classes of RNA and both ribosomal sub-units. Polysome formation is likewise inhibited. However, in E. coli nfr-207 a mutant of B/r which lacks nitrofurazone-reductase I, the synthesis of RNA, ribosomal sub-units and formation of polysomes are not significantly affected. This result implies that a reduced metabolite of the drug rather than the drug itself is the active agent. The ability of ribosomes isolated from nitrofurazone-treated E. coli B/r to carry out poly-U directed polyphenylalanine synthesis was lower than that of ribosomes from untreated cells. 14C from labelled nitrofurazone was found to bind to ribosomal sub-units.

DNA-Directed RNA Polymerases↗
PubMed1975

Effect of activated nitrofurans on DNA.

Enzymically activated nitrofurazone reacts with co-valently closed circular DNA (derived from Escherichia coli minicells carrying lambdadv) to give at least two kinds of damage: breaks which are detected on neutral sucrose gradients and alkali-labile lesions in DNA which are converted to breaks when the DNA is subsequently Treated with alkali. DNA, isolated from nimicells exposed to the drug, also contains lesions which are converted to breaks upon treatment with endonuclease preparations obtained from Micrococcus luteus. Minicells repaired both breaks and nuclease-susceptible lesions within 2 h but did not repair alkali labile lesions within that time. Experiments with three other nitrofurans show that there are considerable differences in the degree to which DNA is damaged by activated metabolites of various derivatives and that the potency of the compounds as mutagens and carcinogens is correlated with the amount of damage caused to minicell DNA.

Binding Sites↗
PubMed1975

Nitrofurazone-reducing enzymes in E. coli and their role in drug activation in vivo.

Earlier work showed that Escherichia coli contains at least two enzymes which reduce nitrofurazone and other nitrofuran derivatives. One of these enzymes is lacking in some nitrofurazone-resistant mutant strains. We now report that there are three separable nitrofuran reductases in this organism: reductase I (mol. wt. approximately 50 000, insensitive to O2), reductase IIa (mol. wt. approximately 120 000, inhibited by oxygen), reductase IIb (mol. wt. approximately 700 000, inhibited by O2). Unstable metabolites formed during the reduction of nitrofurazone by preparations containing reductases IIa and IIb produce breaks in DNA in vitro. In vivo experiments with nitrofurazone-resistant strains, which lack reductase II but contain reductases IIa and IIb, demonstrated that lethality, mutation, and DNA breakage are all greatly increased when cultures are incubated under anaerobic conditions, i.e., conditions such that reductase II is active. These results provide further evidence for the importance of reductive activation of nitrofurazone.

Aerobiosis↗
PubMedDate not supplied

Modulation of cytokine responses of murine CD8+ alphabeta intestinal intraepithelial lymphocytes by IL-4 and IL-12.

The immune responses of the intestine mucosa feature the noninflammatory type, such as IgA production and oral tolerance. Th2 type cytokines have been implicated in the induction of these noninflammatory responses. In the present study, cytokine responses of CD8+ and CD4+ TCRalphabeta+ intestinal intraepithelial lymphocyte (alphabeta iIEL) subsets to TCR stimulation under the influence of IL-12, IL-4, or CD28 costimulation were examined. IL-12 enhanced production of IL-10 and IFN-gamma by the CD8alphabeta+ alphabeta iIEL significantly but only marginally affected the CD8alphaalpha+ subset, whereas IL-4 induced IL-4, IL-5, and IL-10 production and augmented TGF-beta production by both subsets. CD28 costimulation induced production of Th2 cytokines by CD4+ iIEL in the absence of exogenous IL-4. Unlike lymph node CD4+ cells, the CD28 costimulation-induced Th2 differentiation of CD4+ iIEL was not inhibited by IFN-gamma. These results demonstrate active cytokine production by CD4+, CD8alphabeta+, as well as CD8alphaalpha+ alphabeta iIEL. The Th2- skewed cytokine profile of CD8alphaalpha+ alphabeta iIEL and the IFN-gamma-resistance of Th2 differentiation of the CD4+ alphabeta iIEL suggest that both iIEL subsets contribute to the induction of noninflammatory mucosal immune responses.

Animals↗
PubMedDate not supplied

MRCP of congenital pancreaticobiliary malformation.

BACKGROUND: Congenital pancreaticobiliary malformations are sometimes associated with acute or chronic pancreatitis and biliary carcinoma. Currently, magnetic resonance cholangiopancreatography (MRCP) is one of the first choices for investigating and diagnosing pancreaticobiliary diseases noninvasively. We compared the accuracy of conventional MRCP and endoscopic retrograde cholangiopancreatography (ERCP) in making the diagnosis of congenital pancreaticobiliary malformations. METHODS: In patients with pancreas divisum (n = 17), pancreaticobiliary maljunction (n = 12), choledochocele (n = 2), and annular pancreas (n = 1) who underwent ERCP and MRCP, the diagnostic accuracy and findings on MRCP were compared with those on ERCP. RESULTS: Of the 32 patients with congenital pancreaticobiliary malformations diagnosed on ERCP, 23 (72%) presented the same diagnosis on MRCP. Complete pancreas divisum was diagnosed in 73% on MRCP based on the finding of a dominant dorsal pancreatic duct crossing the lower bile duct and emptying into the duodenum without communicating with the ventral pancreatic duct. Pancreaticobiliary maljunction was diagnosed in 75% on MRCP based on the finding of an anomalous union between the common bile duct and the pancreatic duct and the existence of a long common channel. CONCLUSIONS: Conventional MRCP is a useful, noninvasive tool for diagnosing congenital pancreaticobiliary malformations; and the diagnostic accuracy can be increased with three-dimensional MRCP or dynamic MRCP with secretin stimulation.

Bile Ducts↗
PubMedDate not supplied

Structure of human calcitonin gene-related peptide (hCGRP) and of its antagonist hCGRP 8-37 as determined by NMR and molecular modeling.

The solution structures of human calcitonin gene-related peptide (hCGRP, 37 residues) and of its antagonistic fragment hCGRP 8-37 have been determined by two-dimensional 1H nuclear magnetic resonance (NMR) spectroscopy and molecular modeling. Analysis of the double quantum filtered correlation spectroscopy, total correlation spectroscopy and nuclear Overhauser enhancement spectroscopy spectra led to a complete assignment and to the identification of more than 350 intra- and interresidue connectivities for each peptide. Molecular models were calculated by molecular dynamics and energy minimization using distance constraints. The structure of hCGRP is characterized by a rigid N-terminal disulfide-bonded loop followed by helix segments (Val8-Leu16), a gamma-turn (Ser19-Gly21) and several local hydrogen-bonded patterns. The structure of hCGRP 8-37 is less defined than the structure of hCGRP and no helix structure is present. Molecular models of both peptides are consistent with the NH temperature coefficients and secondary chemical shifts of the alpha-protons. Hydrogen bonding with the disulfide-bonded ring appears to be critical for helix formation, both structural elements being essential for agonistic activity.

Amino Acid Sequence↗
PubMedDate not supplied

The role of juxtapapillary duodenal diverticulum in the formation of gallbladder stones.

BACKGROUND/AIMS: Juxtapapillary diverticula (JPD) are considered to be associated with choledocholithiasis but not with cholecystolithiasis. However, there have been few comparative studies on the relationship between JPD and cholecystolithiasis under strict matching for sex and age. METHODOLOGY: Among 4542 consecutive ERCPs at Tokyo Metropolitan Komagome Hospital, 549 patients who were 63 years of age or older were enrolled in this study and were matched for sex and age. They were divided into two groups: with and without JPD. Firstly, the frequency of cholecystolithiasis was compared between the two groups. Next, we recruited 83 patients whose JPD size could be measured by the ERCP films and investigated the relationship between JPD size and gallstones. RESULTS: We found no correlation between JPD and the overall frequency of cholecystolithiasis. However, an analysis of 83 patients with measurable JPD revealed that the size of JPD was closely linked to the occurrence of cholecystolithiasis. The JPD size was statistically larger in patients with cholecystolithiasis than those without. Moreover, when the mean diameter of JPD was 20 mm or more, the incidence of cholecystolithiasis rose up to 73.3%, which was significantly greater compared to the incidence in patients without JPD (p< 0.05). CONCLUSION: A larger JPD may play a role in the formation of gallbladder stones.

Aged↗