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Biomedical subjects

D Li

Publications and source records attributed to D Li.

At least 685 records · Page 38Linked to original sources
PubMed1995

Enzyme-enzyme interaction in the chloroplast: glyceraldehyde-3-phosphate dehydrogenase, triose phosphate isomerase and aldolase.

Apparent physical interaction between pea chloroplast (Pisum sativum L.) glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13) and aldolase (EC 4.1.2.13) is seen in phase-partitioning, fluorescent-anisotropy and isoelectric-focusing experiments. Similarly, results obtained in phase-partitioning and isoelectric-focusing experiments indicate physical interaction between aldolase and triose-phosphate isomerase (EC 5.3.1.1). Kinetic experiments suggest that both aldolase-bound glyceraldehyde-3-phosphate can act as substrate for glyceraldehyde-3-phosphate dehydrogenase. These results are consistent with the notion that there is interaction between these three enzymes both during photosynthetic CO2 fixation and during glycolysis in the chloroplast.

Amino Acid Sequence↗
PubMed1995

15N resonance assignments of oxidized and reduced Chromatium vinosum high-potential iron protein.

The 15N resonances in reduced and oxidized Chromatium vinosum high-potential iron protein have been assigned by use of 1H-1H COSY spectra and 1H-15N HMQC. HMQC-COSY, and HMQC-NOESY spectra. Unambiguous assignment of 70 of 85 backbone 15N resonances in the reduced protein and 62 of 85 resonances in the oxidized protein are made, as are 12 of 21 side-chain 15N resonances.

Amino Acid Sequence↗
PubMed1995

Construction of shuttle expression plasmid and stable expression of foreign gene in mycobacteria and E. coli.

By employing the pUC19 as a backbone, the regulatory and signal sequences which encode kanamycin resistance, and mycobacterial plasmid origin of replication (oriM) were cloned into the pUC19. The recombinant E. Coli-mycobacteria shuttle expression plasmid pBCG-8000 was constructed. The pBCG-8000 was able to replicate in both E. Coli and mycobacteria (including BCG) systems, and to confer stable kanamycin resistance upon transformants. The study should facilitate the development of BCG and other mycobacteria into multivalent vaccine vectors.

BCG Vaccine↗
PubMed1995

Microsatellite instability in colorectal cancer: improved assessment using fluorescent polymerase chain reaction.

BACKGROUND & AIMS: Microsatellite instability was first described in hereditary nonpolyposis colorectal cancers and sporadic colorectal cancers, in which it was associated with a good prognosis. The aim of this study was to assess the advantages of a novel fluorescent assay for detecting microsatellite instability. METHODS: Eleven fluorescently tagged microsatellites and an automated DNA sequencer were used to investigate 54 sporadic colorectal adenocarcinomas. RESULTS: This fluorescent assay combined accurate allele sizing with cross-sectional data display and allowed improved assessment of microsatellite instability. Twenty-two percent of cancers (12 of 54) showed microsatellite instability with at least one marker. For tumors showing microsatellite instability, results were obtained for a minimum of eight markers. Six tumors showed microsatellite instability at high frequency (at least 63% of markers affected), and 42% of the patients who had a tumor showing microsatellite instability had a synchronous and/or metachronous colorectal tumor (vs. 7% of patients whose tumor did not show microsatellite instability). Patients with a microsatellite instability-positive tumor had an improved prognosis (P = 0.03). CONCLUSIONS: The use of this fluorescent assay improved the assessment of microsatellite instability with the automated analysis and cross-sectional data display. The assay identified a subgroup of patients who showed microsatellite instability and who also showed clinical features that differed from the microsatellite instability-negative cases.

Adenocarcinoma↗
PubMed1995

Barrett's epithelium with complete stricture of the esophagus: hypothesis of its etiology.

A 4-year-old very debilitated boy, who suffered from recurrent vomiting (regurgitation) since birth, is described. At the age of 18 months, partial obstruction of the esophagus was apparent, and only semisolid food could be swallowed. The signs of obstruction progressed, and the child was admitted urgently, at the age of 4 years, to the authors' department because of severe dehydration. After resuscitation, a barium swallow and esophagoscopy showed a complete obstruction of the esophagus between its middle and lower third. Through a left thoracotomy incision, 4 cm of the diseased esophagus were resected and continually established by end-to-end esophagoesophageal anastomosis. Pathological examination showed complete obstruction of the esophagus with Barrett's epithelium above and below the stricture. Severe periesophagitis was also present because of sealed perforation of the esophagus. One week after the operation the child was on a normal diet. On follow-up, 6 months later, he has no signs of obstruction and is gaining weight. It is postulated that the presence of Barrett's epithelium in the esophagus in congenital, but the complications, such as stricture formation, are usually caused by chronic irritation, such as gastroesophageal reflux. Barrett's epithelium alone infrequently will cause

Barrett Esophagus↗
PubMed1995

DNA adducts induced by lipids and lipid peroxidation products: possible relationships to I-compounds.

A methanol-extractable lipid fraction of oats has been found previously to induce three specific I-compounds (age-dependent covalent DNA modifications) in female rat liver DNA, as detected by the 32P-postlabeling assay. The current report used an in vitro system to explore the possible mechanisms involved in the formation of these DNA derivatives. Ground oats or commercial oatmeal were extracted with methanol, and the extracts were incubated with rat lung DNA in vitro. DNA was recovered and analyzed by the nuclease P1-enhanced version of the 32P-postlabeling assay. A number of adducts were induced by the in vitro reaction but none of them was identical by chromatographic analysis to oats-specific I-compounds detected in vivo. Addition of rat liver microsomes and cofactors (NADPH or cumene hydroperoxide) to the in vitro reaction also failed to induce any of the oats-specific I-compounds. Pretreatment of oat lipids with soybean lipoxidase and oxygen enhanced formation of most adducts formed in vitro in a dose- and time-dependent manner. Several of these adducts were related to peroxide derivatives of linoleic acid. Chromatographic evidence suggests that one of the major adducts is derived from 4-hydroxynonenal, a reactive intermediate lipid peroxidation product. This adduct was detectable in liver and kidney DNA of untreated rats and its level increased with age. These results were in line with previous in vivo results, suggesting that the oats-specific I-compounds are presumably formed via an indirect mechanism rather than by direct binding of oats components to DNA.

Aging↗
PubMed1995

Biostructural chemistry of magnesium. regulation of mithramycin-DNA interactions by Mg2+ coordination.

Divalent magnesium promotes the selective binding of mithramycin to a cognate DNA sequence (5'-XXGCXX-3') by a coupled mechanism requiring local conformational changes in the polynucleotide backbone and a structural rearrangement of the mithramycin dimer. Circular dichroism, 31P-NMR, and analysis of the topological change of supercoiled plasmid DNA by agarose gel electrophoresis support these conclusions and offer insight on the regulatory role of Mg2+. Molecular modeling suggests that sequence selectivity arises from preferential coordination of Mg2+ to d(GpC) domains in the minor groove of Z-type DNA. We suggest a specific structural role for the essential divalent magnesium ion, and propose a revision of the binding mechanism previously devised for the mithramycin/DNA complex. This revised structural model is entirely consistent with NMR results reported for the mithramycin and related chromomycin complexes, but previously interpreted in terms of an A-type configuration.

Cations, Divalent↗
PubMed1995

Hearing loss and cochlear abnormalities in the congenital hypothyroid (hyt/hyt) mouse.

The congenital hypothyroid (hyt/hyt) mouse has been described as having a homozygous recessive mutation of a single locus on chromosome 12 which results in significant endocrine hypofunction and retarded growth. Although a distinct correlation between inherited hypothyroidism and hearing loss in humans exists, there has been no previous evaluation of the auditory system in these mutant mice. We determined hearing thresholds by auditory-evoked brainstem response testing and noted a 40-45 dB elevation in the hyt/hyt mouse compared to littermate heterozygote (hyt/+) animals and normal progenitor controls BALB/cByJ (+/+). Conventional light microscopy was used to examine the general anatomy of the cochlea in these animals, and the surface structure of the organ of Corti was further evaluated with scanning electron microscopy. Heterozygote and normal control mice had no significant abnormalities of the cochlea, however the hyt/hyt mice displayed consistent morphologic abnormalities of the stereocilia on both inner and outer hair cell systems. The surrounding and supporting cells were identified in the cochleas of the hypothyroid mouse and control animals and showed no significant histologic abnormalities. The auditory, histologic, and ultrastructural characterization of this model provides a foundation for evaluating the effects of true inherited hypothyroidism on auditory pathway development.

Animals↗
PubMed1995

Engineering a domain-locking disulfide into a bacterial malate dehydrogenase produces a redox-sensitive enzyme.

Light-dependent reduction of cystine disulfide bonds results in activation of several of the enzymes of photosynthetic carbon metabolism within the chloroplast. We have modeled the tertiary structure of four of these light-activated enzymes, namely NADP-linked malate dehydrogenase, glyceraldehyde-3-P dehydrogenase, fructosebisphosphatase, and sedoheptulosebisphosphatase, and identified cysteines in each enzyme that be expected to form inactivating disulfide bonds (Li, D., F. J. Stevens, M. Schiffer, and L. E. Anderson, 1994. Biophys. J. 67:29-35). We have now converted two residues in the Escherichia coli NAD-linked malate dehydrogenase to cysteines and produced a redox-sensitive enzyme. Oxidation of domain-locking cysteine residues in the mutant enzyme clearly mimics dark inactivation of the redox-sensitive chloroplast dehydrogenase. This result is completely consistent with our proposed mechanism.

Base Sequence↗
PubMed1995

Triterpenoid saponins from Clinopodium chinensis.

Two new triterpenoid saponins, 3 beta,16 beta,23-trihydroxy-13,28-epoxyolean- 11-en-3-yl-[beta-D-glucopyranosyl(1-->4)-beta-D-glucopyranosyl(1-->3)]- [beta-D-glucopyranosyl(1-->2)]-beta-D-fucopyranoside[1](clinopodiside B) and 28-O-beta-D-glucopyranosyl-3 beta,23-dihydroxyoleana-12,21-dien-3-yl-beta-D-glucopyranosy l-(1-->3)-beta-D- fucopyranoside [3] (clinopodiside C), together with three known saikosaponins, buddlejasaponins IV, IVa, and IVb, have been isolated from the plant, Clinopodium chinensis, and characterized using chemical evidence and spectroscopic methods, in particular 2D nmr spectroscopy.

Carbohydrate Sequence↗
PubMed1995

Oleanane triterpene saponins from the Chinese medicinal herb Clinopodium chinensis.

Four oleanne triterpene saponins, 3beta,16beta, 23-trihydroxy-keton-13beta,28-epoxyolean-9(11)-en-3-yl -[beta-D-glucopranosyl(1-->2)]-[beta-D-glucopyranosyl(1-->3)]-beta -D-fucopyranoside [1] (clinopodiside D), 16beta-propionyl-3beta,23-dihydroxyoleana-11-21-dien-3 -yl-[beta-D-glucopyranosyl(1-->2)]-[beta-D-glucopranosyl(1-->3)]-b eta-D-fucopyranoside [2] (clinipodiside E), 3beta,16beta,21alpha,23,28-pentahydroxy-11-methoxyolean++ +-12-en-3-yl-[beta-D-glucopyranolyl(1-->2)]-[beta-D-glucopyranosyl (1-->3)]-beta-D-fucopyranoside [3] (clinopodiside F), and 3beta,16beta,21beta,23,28-pentahydroxyoleana-11,13(18) -dien-3-yl-[beta-D-glucopyranosyl(1-->2)]-[beta-D-glucopyranosyl(1 -->3)]-beta-D-fucopyranoside [4] (clinopodiside G), were isolated and purified from the plant Clinopodium chinensis. Their structures were elucidated on the basis of interpretation of nmr and ms data and from chemical evidence. The results are of potential interest for medicinal reasons.

Carbohydrate Sequence↗
PubMed1995

Triterpenoid saponins from Gypsophila oldhamiana.

Three new triterpenoid saponins were isolated from the roots of Gypsophila oldhamiana. Their structures were elucidated, using a combination of homonuclear and heteronuclear 2D nmr and fabms, as 3-0-beta-D-galactopyranosyl-(1-->2)-[beta-D-xylopyranolyl-(1-->3)] -beta-D-glucuronopyranosyl quillaic acid methyl ester [1], 3-0-beta-D-galactopyranosyl-(1-->2)-[beta-D-xylopyranosyl-(1-->3)]-beta- D-glucuronopyranosyl gypsogenin methyl ester [2], and 3-0-beta-D-galactopyranolsyl-(1-->2)-[beta-D-xylopyranosyl-(1-->3) ]-beta-D-glucuronopyranosyl quillaic acid 28-[0-beta-D-fucopyranosyl(1-->4)-beta-D-glucopyranosyl(1-->3)]-alpha-L- rhamnopyranosyl] ester.

Carbohydrate Sequence↗
PubMed1995

The antinociceptive effect of S-(+)-ibuprofen in rabbits: epidural versus intravenous administration.

This study was designed to determine whether systemic absorption plays any role in the antinociceptive effect of epidural (EP) sodium S(+)-ibuprofen (IB). One week after surgical implantation of EP catheters, six rabbits were given EP injections with either normal saline (NS) 0.4 mL or IB 10 mg in 0.4 mL NS (Group 1) on separate days. Each animal was injected with IB 10 mg intravenously (i.v.) on another day. Six control rabbits (Group 2) had neither surgery nor any injection. Analgesic testing was performed using electric stimulation through two electrocardiogram (ECG) skin electrodes with built-in adhesive, attached to shaved hip areas using 50 V, 1 Hz, 3 ms, before and 0.5,1,2 and 3 h after injection in Group 1, and in similar times in controls. The 95% confidence intervals (CI) of the mean difference between baseline and maximal nociceptive response latency of all groups were compared using analysis of covariance (ANCOVA) adjusted for baseline measurements. This comparison covered all possible pairs among all groups. Significant antinociceptive effects were seen after EP IB but not after control or i.v. IB. Neither motor dysfunction nor evidence of systemic toxicity or neurotoxicity was observed in any animal.

Analgesics↗
PubMed1995

HIV risk behaviors but absence of infection among drug users in detoxification centers outside Yunnan province, China, 1993.

OBJECTIVES: To date, HIV spread in China has occurred principally among injecting drug users (IDU) in remote border regions of Yunnan province. We therefore sought to better understand the risks for and prevalence of HIV infection among drug users in parts of China outside Yunnan province. METHODS: A behavioral survey of drug use and AIDS-related knowledge was conducted among all consenting drug users who entered treatment from 1 November to 31 December 1993 in seven provincial drug detoxification centers outside Yunnan province. After giving verbal informed consent, all drug users were tested for HIV. RESULTS: Of the 1293 study participants, 207 (16%) reported injecting drugs. The proportion of IDU among all drug users varied widely by region, from 1% in Sha'anxi and Gansu provinces in the northwest region to 58% in Guangxi province in the south. IDU were more likely than non-IDU to be single and unemployed or self-employed, but did not differ in other demographic aspects. Among all drug users, 2% reported sharing needles without cleaning equipment, while 5% shared with some cleaning. Although 1060 (82%) drug users had heard of AIDS and most knew about its sexual (79%), parenteral (77%), and perinatal (60%) modes of transmission, many had misconceptions about its spread by casual contact. Of the 207 IDU tested for HIV, none were HIV-positive (95% confidence interval, 0--1.4). CONCLUSION: The absence of HIV infections detected in this study suggests that the prevalence of HIV is currently low among IDU in China outside the Yunnan province. However, the behavior of these IDU puts them at high risk for HIV infection. Prevention efforts are needed to prevent the spread of HIV among IDU throughout China and to avoid the experience of neighboring countries in Asia.

Adolescent↗