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Biomedical subjects

L Lee

Publications and source records attributed to L Lee.

At least 163 records · Page 9Linked to original sources
PubMed1995

The occurrence of C-H...O hydrogen bonds in proteins.

Hydrogen bonds are a major feature of protein structure. By a generally accepted definition, they occur whenever a proton is shared by two electronegative atoms. Hence, only hydrogens bonded to nitrogen and oxygen atoms are usually considered in analyses of protein hydrogen bond networks. However, X-ray and neutron diffraction studies have shown that crystals of various organic compounds exhibit close C-H...X contacts (where X is an electronegative atom, in most cases oxygen) which show all the stereochemical hallmarks of hydrogen bonds. In this work, we describe an analysis of short C-H...O interactions in a sample of known protein structures representing different categories of tertiary folds and refined at a resolution of at least 2 A. Although our analysis is based on the calculated coordinates of hydrogen atoms, its results are statistically significant: we find strong evidence that a large percentage of short C...O contacts constitute cohesive interactions. Moreover, the stereochemical study of C-H...O = C contacts, in which the orientation of free electron orbitals on the acceptor oxygen atom can be predicted, reveals that these interactions exhibit stereochemical features typical of hydrogen bonds. Among the hydrogen atoms involved in these contacts, the most common are those bonded to alpha carbon. This is consistent with the fact that these hydrogens are more acidic than others. We describe four different categories of C-H...O = C bonds. Those found between C alpha-H groups and main chain oxygens in adjacent strands of beta sheets are the most ubiquitous. Our results call for a revision of crystallographic restrained refinement programs which treat close carbon-oxygen contacts as purely repulsive; they may also have implications for the understanding of some enzymatic reaction mechanisms.

Carbon↗
PubMed1995

Ligation of the T-cell antigen receptor (TCR) induces association of hSos1, ZAP-70, phospholipase C-gamma 1, and other phosphoproteins with Grb2 and the zeta-chain of the TCR.

Signaling by the T-cell antigen receptor (TCR) involves both phospholipase C (PLC)-gamma 1 and p21ras activation. While failing to induce Shc/Grb2 association, ligation of the TCR/CD3 receptor in Jurkat T-cells induced hSos1-Grb2 complexes. In addition to hSos1, Grb2 participates in the formation of a tyrosine phosphoprotein complex that includes 145-, 95-, 70-, 54-, and 36-38-kDa proteins. p145 was identified as PLC-gamma 1 and p70 as the protein tyrosine kinase, ZAP-70. Although of the same molecular weight, p95 was not recognized by an anti-serum to p95 Vav. The SH2 domains of Grb2 and PLC-gamma 1 were required for the formation of this protein complex. In anti-CD3-treated cells, Grb2 redistributed from the cytosol to a particulate cell compartment along with p36/p38, ZAP-70, and PLC-gamma 1. Part of the Grb2 complex associated with the particulate compartment could be extracted with Nonidet P-40, while the rest was Nonidet P-40 insoluble. In both the detergent-soluble and -insoluble fractions, Grb2 coimmunoprecipitated with the zeta-chain of the TCR. Taken together, these results indicate that anti-CD3 induces Grb2-hSos1-PLC-gamma 1-p36/p38-ZAP70 complexes, which localize in the vicinity of TCR-zeta.

Adaptor Proteins, Signal Transducing↗
PubMed1995

Binding of alpha-dihydrotetrabenazine to the vesicular monoamine transporter is stereospecific.

The two enantiomers of alpha-dihydrotetrabenazine were separated using chiral high performance liquid chromatography. The (+)-isomer showed high affinity in vitro (Ki = 0.97 +/- 0.48 nM) for the vesicular monoamine transporter (VMAT2) in rat brain striatum, whereas the (-)-isomer was inactive (Ki = 2.2 +/- 0.3 microM). Each isomer was then synthesized in carbon-11 labeled form, and regional brain biodistributions in mice determined after intravenous injection. Only (+)-alpha-dihydrotetrabenazine showed selective and specific accumulations in regions of dense monoaminergic innervation (e.g., striatum, hypothalamus), which could be blocked by coinjection of unlabeled tetrabenazine. Binding of alpha-dihydrotetrabenazine to the vesicular monoamine transporter is thus stereospecific.

Animals↗
PubMed1995

Effects of nisoldipine in silent myocardial ischemia after healing of acute myocardial infarction.

Silent myocardial ischemia occurring after acute myocardial infarction is classified as Cohn type II and has a frequency of 20-30% in all patients with acute myocardial infarction. Follow-up data of patients with either silent or anginal ischemia show a poor prognosis. Thus, all ischemic episodes occurring after myocardial infarction should be treated aggressively. Many multicenter studies have evaluated whether drug treatment can improve prognosis or protect from a nonfatal second attack. Calcium antagonists, especially those that increase heart rate, have not been considered as drugs of choice for this purpose, despite the many beneficial effects shown on myocardial tissue in experimental studies. In the study reported here, the effect of nisoldipine on postinfarction silent myocardial ischemia was evaluated by ambulatory left ventricular function monitoring. Ten patients were selected for study who showed silent myocardial ischemia after their first acute infarction. Blood pressure fell significantly (p < 0.05) after 4 weeks of treatment with nisoldipine (5-10 mg/day), but heart rate showed no change at rest. Exercise time improved (p < 0.05), with increased peak double products. During exercise, there was no significant change in end-diastolic volume but there was a marked improvement in end-systolic volume, and at the submaximal point the ejection fraction was significantly (p < 0.05) increased. Ejection fraction at rest also improved. The deterioration in ejection fraction due to dipyridamole was ameliorated by nisoldipine. Ejection fraction and blood pressure improved during the calculation test, and work performance also improved.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Tolerance induced by direct inoculation of donor antigen into the thymus in low and high responder rodents.

A novel approach to tolerance induction in rats was recently described where donor antigen is inoculated directly into the thymus along with a brief period of immunosuppression in a pretransplant strategy. To develop a strategy that has more clinical appeal, we evaluated the timing of donor antigen inoculation in relation to allografting, the use of frozen bone marrow as the antigen, and the dose response of purified T cells as the antigen in a low responder heterotopic heart allograft combination. Additionally, the success of this pretransplant strategy in different low and high responder strain combinations was defined. In tolerant low responder animals we evaluated in vitro and in vivo cellular immunity. Tolerant host strain naive CD8+ T cell responses to donor and third party stimulators were compared to determine if tolerance is related to the strength of the response of the T cell subsets to donor antigen. Frozen bone marrow can induce tolerance in a low responder combination. Additionally, the dose of purified T cells necessary for tolerance induction was 5 x 10(5) cells. The pretransplant strategy was successful in two low responder strain combinations, Lewis into Wistar Furth and Lewis into DA, but unsuccessful in all high responder strain combinations evaluated. Low responder animals unresponsive to donor heart allografts demonstrate intact cell-mediated immunity and donor-specific tolerance in vivo by rejecting third party but not second donor strain hearts. The in vitro responses of tolerant animals demonstrated donor-specific suppression of the MHC class II response but an intact (normal) response to third party stimulators by proliferation assays and IFN-gamma production, suggesting suppression at the CD4+ T cell subset level.

Animals↗
PubMed1995

Identification of the site of non-enzymatic glycation of glutathione peroxidase: rationalization of the glycation-related catalytic alterations on the basis of three-dimensional protein structure.

Bovine erythrocyte glutathione peroxidase has been glycated in vitro by incubation in 0.05 M glucose at pH 7.4. Upon glycation the estimated KM for t-butylhydroperoxide reduction increased by approx. 3-fold in comparison to non-glycated glutathione peroxidase. The glycated protein fraction was stabilized by NaBH4 reduction and subjected to tryptic cleavage. Affinity chromatography of the tryptic digest on m-aminophenylboronate-Agarose resulted in the isolation of a single glycated peptide. The peptide was identified as T94-K117 by amino-acid composition comparison to the published amino-acid sequence for this enzyme. The glycation site has been identified as the epsilon-NH2 group of K110. Examination of the three-dimensional structure of bovine erythrocyte glutathione peroxidase indicates that K110 lies on the surface of the protein approximately 15 A away from the active site selenocysteine (SEC 45). Modeling studies indicate that K110 can communicate via H-bonded interactions with the alpha-helix containing the active site residues (SEC-45 and R50). The observed elevation of KM upon glycation of bovine glutathione peroxidase is discussed in terms of the disruption of the long range H-bonded interaction.

Animals↗
PubMed1995

A comparison of spontaneous versus induced tolerance in an experimental model of rat hepatic allograft transplantation.

In some rodent haplotype combinations, spontaneous tolerance (ST) develops after orthotopic liver transplantation (OLT) without any immunosuppression [e.g., Lewis (Lew, RT1) into Wistar Furth (WF, RT1u)] whereas in other combinations vigorous, progressive rejection rapidly leads to the death of the recipients. We (and others) have induced tolerance (IT) in a rejecting strain combination [Dark Agouti (DA, RT1a) into Lew] by intrathymic inoculation of donor bone marrow cells and 1 cc of antilymphocyte serum (ALS) 7-14 days prior to OLT. We hypothesized that cellular immunity in the two groups of animals was similar. We first compared survival in each group of animals and found that there was no difference in the number of animals surviving > 100 days (8/11 vs 16/17, ST vs IT, respectively, P = 0.11). Liver function studies were similar in these animals at 2 and 4 weeks after OLT and comparable to syngeneic Lew into Lew OLT animals, but significantly lower than in the rejecting DA into Lew combination treated with only ALS. Animals that were unresponsive to their allografts demonstrated donor-specific tolerance by the acceptance of donor strain (n = 4, ST and IT) and rejection of third party (n = 1 and n = 2, ST and IT groups, respectively) heterotopic heart allografts. One-way mixed lymphocyte cultures (MLC) of peripheral blood lymphocytes against donor and third party antigen were suppressed to donor and third party stimulators versus the MLC of unmanipulated animals. Naive host strain responder lymph node cells and purified T cells demonstrated strong proliferative responses to donor strain antigen in both the ST and IT animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Experimental assessment of a new, low-cost antivenom for treatment of carpet viper (Echis ocellatus) envenoming.

Morbidity and mortality due to envenoming by the carpet viper (Echis ocellatus) in northern Nigeria remains unacceptably high and constitutes a severe economic and public health problem to the local farming community in particular. The only effective treatment of systemic envenoming is antivenom, but supplies are very limited as the little that is available is either too expensive, ineffective or both. Here, we describe a new ovine antivenom, designed both to be effective and to be available at low cost. The antivenom, a polyclonal ovine Fab preparation, provides superior protection, both in vivo and in vitro, to the best alternatives, the monospecific South African Institute of Medical Research antivenom and the polyspecific Pasteur Isper Africa antivenom. Fab fragments, which have the advantages of large volumes of distribution and, theoretically, low immuno-reactivity, are produced by a reusable solid-phase papain matrix which eliminates enzyme contamination of the product and reduces cost. The antivenom is lyophilised for increased stability and extended shelf-life in tropical climates where it is often impossible to keep such products cool.

Animals↗
PubMed1995

Isolation and expression analysis of tyro3, a murine growth factor receptor tyrosine kinase preferentially expressed in adult brain.

Growth factors and their receptors function in the nervous system to induce proliferation and differentiation of neuronal precursor cells and to support survival of mature neurons. We have isolated a murine growth factor receptor tyrosine kinase using an anti-phosphotyrosine antibody screening procedure and studied the pattern of expression. The deduced amino acid sequence of the kinase has all the characteristics of a growth factor receptor and consists of a putative extracellular domain, a transmembrane domain, and a tyrosine kinase domain. Sequence comparison with known receptor tyrosine kinases indicated that the murine kinase is a mouse homolog of tyro3. tyro3 belongs to the Axl/Ufo growth factor receptor family. In the putative extracellular domain, there are two Ig-like domains and two fibronectin type III repeats which are conserved in other members of the Axl/Ufo family receptors. Northern blot hybridization analysis showed that tyro3 is expressed at high levels in the brain of adult mice, although considerable expression was also observed in the testis. In situ hybridization analysis revealed that high levels of tyro3 are expressed in the cerebral cortex, the lateral septum, the hippocampus, the olfactory bulb, and in the cerebellum. The highest levels of tyro3 expression in the brain are associated with neurons. The preferential expression of tyro3 in specific regions of the adult mouse brain suggests that tyro3 may function as a novel neurotrophic factor receptor.

Amino Acid Sequence↗
PubMed1995

The value of vocal function exercises in the practice regimen of singers.

The purpose of this study was to investigate the effects of isometric-isotonic vocal function exercises, practiced regularly for 4 weeks, on parameters of voice production in the healthy singer. A total of 20 university graduate-level voice majors of similar age and vocal training were divided into experimental and control groups, each containing 3 men and 7 women. Each group continued their regular singing practice regimen and the experimental group added the vocal function exercise program. Assessment included acoustic and aerodynamic measures, videostroboscopic ratings, and subjective evaluations. Experimental subjects demonstrated significant improvements in posttest aerodynamic measures of flow rate, phonation volume, and maximum phonation times, suggesting an increase in glottal efficiency.

Acoustics↗
PubMed1995

Objective measures of voice production in normal subjects following prolonged voice use.

Laryngeal fatigue affects the physical sensations, effort, and perceptual quality of voice production. The underlying physiology of fatigue is not well understood. Acoustic, aerodynamic, and videostroboscopic data were measured in 10 normal speakers before and after prolonged voice use. Significant changes were found in the fundamental frequency of connected speech. Anterior glottal chinks were induced in a majority of subjects. Implications are discussed.

Adult↗
PubMed1995

Radiographic differentiation of osteogenic sarcoma, osteomyelitis, and fibrous dysplasia of the jaws.

UNLABELLED: Biopsy and histopathologic analysis may fail to consistently separate osteogenic sarcoma, osteomyelitis, and fibrous dysplasia. OBJECTIVES: To establish useful radiographic characteristics to differentiate these diseases, an objective preliminary study of radiographs of 30 cases of these diseases was done. STUDY DESIGN: After precisely defining several radiographic characteristics and completing a calibration study, three observers unaware of the diagnosis examined study cases that were randomly ordered. RESULTS: Despite using trained observers and strict criteria, differentiation of the three conditions is difficult on the basis of radiographic features alone. In osteogenic sarcoma, the distinguishing features were: permeative lesion borders, stippled bone pattern, destruction of cortical outlines, perpendicular spiculations of periosteal new bone, destruction of lamina dura, and widening of the entire periodontal ligament space. Presence of sequestra and laminations of periosteal new bone were the most useful distinguishing features in cases of osteomyelitis that otherwise resemble fibrous dysplasia. In fibrous dysplasia, superior displacement of the mandibular canal and a fingerprint bone pattern were pathognomonic. Displacement of the maxillary sinus cortex, alteration of lamina dura to the abnormal bone pattern, and narrowing of the periodontal ligament space were also useful distinguishing features. CONCLUSIONS: Our findings indicate that diagnosis cannot rely on radiographic characteristics alone, although some radiographic findings were more useful than others.

Diagnosis, Differential↗
PubMed1995

Nucleotide sequence of tomato ringspot virus RNA1.

The nucleotide sequence of tomato ringspot nepovirus (TomRSV) RNA1 has been determined. TomRSV RNA1 is 8214 nucleotides in length, excluding the 3' poly(A) tail, and contains a single long open reading frame (ORF) of 6591 nucleotides beginning at the first AUG codon at nucleotide position 78. This ORF accounts for 80% of the RNA1 sequence and would give rise to a polyprotein with a predicted molecular mass of 244 kDa. Amino acid sequence comparisons between portions of the TomRSV RNA1-encoded polyprotein and proteins encoded by several members of the picornavirus superfamily have provided information concerning the genomic organization and putative functions of TomRSV-encoded proteins. The putative TomRSV protease retains a conserved histidine residue present in the proteases encoded by members of the como-, poty- and poliovirus groups which is thought to be involved in dipeptide cleavage site recognition. Interestingly, this histidine residue is replaced by a leucine in the proteases of other sequenced nepoviruses. This suggests that the TomRSV protease shares dipeptide cleavage site specificity with that of como-, poty- and picornaviruses rather than the other nepoviruses.

Amino Acid Sequence↗