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Biomedical subjects

Y Kim

Publications and source records attributed to Y Kim.

At least 757 records · Page 42Linked to original sources
PubMed1991

NMR studies of the structure and dynamics of membrane-bound bacteriophage Pf1 coat protein.

Filamentous bacteriophage coat protein undergoes a remarkable structural transition during the viral assembly process as it is transferred from the membrane environment of the cell, where it spans the phospholipid bilayer, to the newly extruded virus particles. Nuclear magnetic resonance (NMR) studies show the membrane-bound form of the 46-residue Pf1 coat protein to be surprisingly complex with five distinct regions. The secondary structure consists of a long hydrophobic helix (residues 19 to 42) that spans the bilayer and a short amphipathic helix (residues 6 to 13) parallel to the plane of the bilayer. The NH2-terminus (residues 1 to 5), the COOH-terminus (residues 43 to 46), and residues 14 to 18 connecting the two helices are mobile. By comparing the structure and dynamics of the membrane-bound coat protein with that of the viral form as determined by NMR and neutron diffraction, essential features of assembly process can be identified.

Capsid↗
PubMed1991

Site-directed mutagenesis of ricin A-chain and implications for the mechanism of action.

Ricin A-chain is an N-glycosidase that attacks ribosomal RNA at a highly conserved adenine residue. The enzyme is representative of a large family of medically significant proteins used in the design of anticancer agents and in the treatment of HIV infection. The x-ray structure has been used as a guide to create several active site mutations by directed mutagenesis of the cloned gene. Glu177 is a key catalytic residue, and conversion to Gln reduces activity 180-fold. Asn209 is shown to participate in substrate binding by kinetic analysis. Conversion to Ser increases Km sixfold but has no effect on kcat. Conversion of Tyr80 and Tyr123 to Phe decreases activity by 15- and 7-fold respectively. A mechanism of action is proposed that involves binding of the substrate adenine in a syn configuration that resembles the transition state; the putative oxycarbonium ion is probably stabilized by interaction with Glu177.

Base Sequence↗
PubMed1991

Orientations of amphipathic helical peptides in membrane bilayers determined by solid-state NMR spectroscopy.

Solid-state NMR spectroscopy was used to determine the orientations of two amphipathic helical peptides associated with lipid bilayers. A single spectral parameter provides sufficient orientational information for these peptides, which are known, from other methods, to be helical. The orientations of the peptides were determined using the 15N chemical shift observed for specifically labeled peptide sites. Magainin, an antibiotic peptide from frog skin, was found to lie in the plane of the bilayer. M2 delta, a helical segment of the nicotinic acetylcholine receptor, was found to span the membrane, perpendicular to the plane of the bilayer. These findings have important implications for the mechanisms of biological functions of these peptides.

Amino Acid Sequence↗
PubMed1991

A preliminary report of combination chemotherapy with cisplatin and mitomycin-C followed by radical hysterectomy or radiation therapy in patients with locally advanced cervical cancer.

Neoadjuvant chemotherapy with cisplatin and mitomycin-C was used in the primary treatment of 17 patients with locally advanced cervical cancer (stages Ib-IIIb; tumor diameter greater than 5 cm) prior to definitive local treatment with radical hysterectomy or radiotherapy. Thirteen of the seventeen patients (76.5%) responded to initial chemotherapy, permitting a radical hysterectomy in ten patients. At histologic examination of the surgically resected primary tumor and lymph nodes, complete pathologic responses were found in 2 patients and partial pathologic responses in 8 patients. The median follow-up time is 14.5 months with a median survival for all patients of 52 weeks. All responders are alive. No therapy-related deaths, major complications, or delay in treatment occurred. Neoadjuvant chemotherapy with mitomycin-C and cisplatin is feasible and may be of benefit for patients with locally advanced cervical cancer.

Adult↗
PubMed1991

High-dose-rate afterloading brachytherapy, external radiation therapy, and combination chemotherapy in poor-prognosis cancer of the cervix.

Fourteen patients with poor-prognosis cervical cancer were treated with concurrent chemotherapy (cisplatin and mitomycin-C), external radiation therapy (RT), and high-dose-rate (HDR) brachytherapy. Pelvic RT was delivered as (a) external-beam radiation (four-field box technique, 40.0 Gy), (b) brachytherapy using HDR 60Co or 192Ir (3.80 Gy/fraction, thrice weekly; total dose, 46.83 Gy) with intrauterine stent, and (c) parametrial boost using an AP field with custom-fabricated step wedges. Post-radical-hysterectomy patients received 50.40 Gy external RT and 3.23 Gy/day vaginal cylinder HDR at 1/2-cm depth (total dose, 16.15 Gy). Complete clinical and radiographic response was noted in all evaluable patients who are alive with no evidence of disease, 3 to 27 months after completion of therapy (median, 9 months). Toxicity consisted of grade 2 to 3 hematologic toxicity (4 patients) and nausea and vomiting in all, but grade 3 in only 2 patients. One patient had grade 2 diarrhea. The only major complication (small bowel obstruction) occurred in a patient with lupus vasculitis. This pilot study demonstrates the feasibility of this regimen in an outpatient setting with acceptable toxicity. More prolonged follow-up of our patients is required to determine its impact on long-term survival.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1991

Transcardiac alteration of neutrophil function before and after coronary thrombolysis in human myocardial infarction.

We examined function of isolated neutrophils taken from aorta and coronary sinus before and after thrombolytic reperfusion in 17 patients whose infarct-related coronary arteries were totally occluded. Before reperfusion in left coronary artery disease, free radical generation by activated neutrophils in coronary sinus, assessed by ferricytochrome c reduction (phorbol myristate acetate, 10 ng/ml) and luminol-enhanced chemiluminescence (A23187, 2 microM), was reduced by 20% (P less than 0.05) and 30% (P less than 0.05), respectively, compared with those in aorta. Neutrophil aggregation (A23187, 10 microM) and chemotactic activity (formyl-methionyl-leucyl-phenylalanine, 5 microM) were also reduced in coronary sinus by 21% and 20%. After reperfusion the extent of such neutrophil function in coronary sinus recovered and was similar to that in aorta. There were no significant differences between neutrophil counts in aorta and coronary sinus before and after reperfusion. In right coronary artery disease, no significant changes were seen in these functions of neutrophils of aorta and coronary sinus before and after reperfusion. These results indicate that function of neutrophils passing through coronary circulation fluctuated significantly in association with reperfusion, suggesting (1) factor(s) that depress neutrophil function are produced in coronary circulation during myocardial ischemia and their effects are overcome after reperfusion or (2) activated neutrophils, trapped in the ischemic coronary bed, are washed out to coronary sinus after reperfusion.

Chemotaxis, Leukocyte↗
PubMed1991

Impact of dietary fatty acid supplementation on renal injury in obese Zucker rats.

We previously reported that renal injury in hyperlipidemic, obese Zucker rats was associated with a relative deficiency of tissue polyunsaturated fatty acids (PUFA). In the present study 10-week-old obese Zucker rats were pair fed regular chow or chow containing either 20% sunflower oil rich in n-6 PUFA, fish oil rich in n-3 PUFA, coconut oil medium-chain saturated fatty acid, or beef tallow long-chain saturated fatty acid. At 34 weeks of age there were comparable reductions in albuminuria, mesangial matrix expansion, and glomerulosclerosis in the fish oil and sunflower oil groups. While both fish oil and sunflower oil reduced serum triglycerides, and improved the composition of triglyceride-enriched lipoproteins, only fish oil decreased serum cholesterol. The effect of the dietary fatty acid supplementation on fatty acid profiles were similar in isolated glomeruli and cortical tissue. In general, the amelioration in injury in the fish oil and sunflower oil fed rats was most closely linked to glomerular levels of PUFA, either n-6 or n-3. These data suggest that hyperlipidemia and abnormalities in tissue FA are closely linked, and that dietary supplementation with PUFA may ameliorate chronic, progressive renal injury.

Albuminuria↗
PubMed1991

Arteriovenous malformation in the cerebellopontine angle presenting as hemifacial spasm--case report.

A 64-year-old female was admitted with a 6-year history of right hemifacial spasm. Neurological examination and precontrast computed tomographic (CT) scanning showed no abnormality. Vertebral angiography disclosed, however, a small arteriovenous malformation (AVM) in the right cerebellopontine angle. A postcontrast CT scan demonstrated a high-density area in the right cerebellomedullary junction which appeared as a flow-void signal on magnetic resonance images. A right retromastoid craniectomy was performed to separate an enlarged and tortuous loop of the right anterior inferior cerebellar artery from the right facial nerve using a Teflon-felt sheet. The AVM was not excised. Postoperatively, she was completely free of hemifacial spasm.

Cerebellopontine Angle↗
PubMed1991

Effects of IGF-I and glucose on protein and proteoglycan synthesis by human fetal mesangial cells in culture.

Abnormalities in proteoglycan metabolism have been implicated in the pathogenesis of diabetic nephropathy. Whether hyperglycemia plays a direct role in these events is unknown. To evaluate the effects of high glucose concentrations and insulinlike growth factor I (IGF-I) on kidney proteoglycan and protein metabolism, we incubated quiescent, subconfluent human fetal mesangial cells for 24 h in serum-free media containing either physiological (5.6-mM) or elevated (25-mM) glucose concentrations with or without 1.3 x 10(-9) M IGF-I. In the presence of physiological glucose concentrations, IGF-I stimulated incorporation of [3H]leucine into protein and [35S]sulfate or [3H]glucosamine into proteoglycans. High glucose concentrations significantly amplified IGF-I-mediated stimulation of protein synthesis but totally abolished IGF-I-induced proteoglycan synthesis. The hydrodynamic size and proportions of heparan-35SO4 and chondroitin/dermatan-35SO4 proteoglycans in all experimental media were the same. However, high glucose concentrations decreased the iduronic acid content of dermatan-35SO4. In separate experiments, quiescent cells were cultured for 7 days in media supplemented with 2% fetal calf serum. IGF-I had no effect on mesangial cell proliferation, but as cells reached confluence, high glucose concentrations significantly inhibited cell proliferation. This inhibition was not mimicked by isosmolar concentrations of mannitol. After 7 days, uptake of radioactive precursors into proteoglycans and proteins over 24 h was similar under all culture conditions. However, IGF-I decreased the ratio of [35S]sulfate to [3H]glucosamine in proteoglycans and their glycosaminoglycan side chains. This difference persisted in disaccharides derived by chondroitin ABC lyase digestion of dermatan-35SO4.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Division↗
PubMed1991

Effect of geometric parameters of perspective on judgements of spatial information.

15 university students performed an exocentric judgement task in which they estimated the azimuth and elevation separating two computer-generated cubes, using a perspective display. The perspective displays were created by varying two geometric parameters of perspective, the geometric field of view and station-point distance. Further, the radial distance separating the computer-generated images was varied. Analysis indicated that azimuth errors varied as a function of geometric field of view, radial distance, and station-point distance, while elevation errors varied as a function of geometric field of view and radial distance.

Adult↗
PubMed1991

Differential expression of basement membrane collagen in membranous nephropathy.

Membranous nephropathy (MN) is characterized by subepithelial immune complex formation and progressive thickening of the glomerular basement membrane (GBM). Kidney tissues from 21 patients stratified according to morphology (stage I: 5 patients; stage II: 5 patients, stage III: 11 patients) were studied by immunohistochemical techniques using antibody probes to matrix components of recently described (novel) chains of type IV collagen [alpha 3(IV)NC, alpha 4(IV)NC, Alport antigen] and of traditional type IV collagen [alpha 1(IV)NC, alpha 2(IV)NC, 7S(IV), triple helix]; as well as laminin B2, nidogen and fibronectin. In Stage I, there were no detectable changes when compared with normal tissue. In Stage II and early Stage III, the subepithelial projections of GBM (spikes) and the thickened GBM consisted predominantly of the novel type IV collagen chains as well as laminin B2 and nidogen, with no detectable changes in traditional type IV collagen. In late Stage III, an increase in the latter was observed in the subendothelial region of the thickened GBM with narrowing of the capillary lumen. At this stage, there was close apposition of novel and traditional type IV collagen molecules. The expression of these two groups of molecules is spatially and temporally distinct during the evolution of MN. It is hypothesized that immune complex formation in the subepithelial region of the GBM leads to increased formation of the novel type IV collagen network by visceral epithelial cells resulting in the formation of spikes and thickening of GBM between and surrounding immune deposits. These changes precede and are distinct from detectable alterations in traditional type IV collagen. With progression and time, the deposits become embedded in the novel collagen network and increased subendothelial formation of traditional type IV collagen molecules occurs with narrowing of the capillary lumen.

Antibodies, Monoclonal↗
PubMed1991

Scanning tunneling microscopy imaging of synthetic oligonucleotides and oligonucleotide-metal complexes.

Scanning tunneling microscopy (STM) has been used to image 12- and 24-base pair (bp) synthetic oligonucleotide duplexes alone or with intercalatively-bound metal complexes with submolecular resolution. The sizes of the 12- and 24-bp oligonucleotides determined from STM images are close to expected values, and images of isolated duplexes resolve the two nucleotide strands of these molecules. The variation of duplex size in our images demonstrates that these features are not due to surface artifacts. In addition, images of the 12-bp duplex in the presence of bis(9,10-phenanthrenequinone diimine)(2,2'-bipyridyl)rhodium(III) exhibit a new structural feature at 14 +/- 2 A from the duplex ends. This new feature corresponds well to the metal binding site determined from DNA cleavage and molecular modeling studies. These results indicate that STM can be used to image directly transition metal complexes bound to DNA, and thus suggest that metal complexes bound specifically to biological molecules could serve as labels in STM structural studies.

2,2'-Dipyridyl↗
PubMed1991

Differential expression of basement membrane collagen chains in diabetic nephropathy.

Diabetic nephropathy is characterized by progressive expansion of mesangial matrix and thickening of the glomerular basement membrane (GBM). Kidney tissues from 13 patients with insulin-dependent diabetes mellitus were studied by immunohistochemical techniques for the distribution of three recently described collagen peptides (M28+, M28 [Good-pasture antigen], and Alport antigen) and various components of classical type IV collagen [alpha 1(IV) noncollagenous (NC) globular domain, alpha 2(IV) NC, 7S, triple helix]. Recently M28 and M28+ were designated as NC monomers of alpha 3(IV) and alpha 4(IV) based on limited amino acid sequencing. During the course of the disease, the distribution of the M28 chains and the Alport peptide segregated completely from that of classical type IV collagen. In diabetic kidneys, antibodies to the M28 and Alport peptides reacted intensely with the thickened GBM but not with the mesangium. In contrast, the reactivity of antibodies to various components of classical type IV collagen was prominent within the expanded mesangial matrix with significant decrease in reactivity in the peripheral capillary wall. In hyalinized glomeruli, components of classical type IV collagen virtually disappeared, whereas the M28 and Alport peptides persisted in the collapsed GBM. These studies support the view that expansion of the mesangial matrix and thickening of the GBM involve separate and distinct collagen components. The differential expression of the M28 and Alport peptides compared with that of classical type IV collagen may be a consequence of differing sites of synthesis (classical type IV collagen from endothelial/mesangial cells and M28 and Alport chains from visceral epithelial cells), independent control mechanisms, and/or differences in degradation.

Antibodies, Monoclonal↗
PubMed1991

Hyperlipidemia and progressive renal disease.

Experimental studies have suggested an important role for abnormal lipid metabolism as an integral factor in modulating progressive renal damage. Dietary induced hypercholesterolemia induced relatively modest glomerular injury. However, in the presence of reduced nephron population or in the presence of underlying renal diseases, such as diabetes, nephrotic syndrome, and hypertension, nephron injury can be markedly exaggerated. These experimental results suggest that an important interaction may occur between renal disease and the occurrence of abnormalities of lipid metabolism. Additional support for the role of lipids in progressive renal injury can be obtained from studies in which pharmacological interventions reduced circulating lipids and this led to decreased glomerular damage. The mechanisms whereby lipids may amplify glomerular injury are not completely understood but may include an interaction with macrophages, alteration in vascular and mesangial functions, changes in production of mediator substances or alterations in membrane fluidity. Local glomerular modification of lipoproteins could also occur and contribute to the development of glomerular pathologic changes. Clinically, few data are available that provide insights into the potential role of renal-related lipid abnormalities in the progression of human renal disease.

Animals↗
PubMed1991

Routine screening for unsuspected aortic aneurysms in patients after myocardial revascularization: a prospective study.

Ultrasonography of the abdominal aorta was routinely performed in a consecutive series of 100 patients during postoperative reconvalescence after myocardial revascularization. The mean aortic diameter was greater in the male series (n = 80) then in the female population (n = 20) (2.17 +/- 0.85 cm vs 1.6 +/- 0.3 cm). Abnormalities were only seen in male patients over 50 years of age (n = 65). The overall incidence of aneurysm greater than or equal to 4 cm was 6%. The incidence of aortas at least 3 cm was 7/65 (11%). It is suggested that the incidence of unsuspected aortic aneurysm in this subgroup is high enough to justify continued screening programmes by ultrasound.

Adult↗