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Biomedical subjects

H K Choi

Publications and source records attributed to H K Choi.

At least 109 records · Page 6Linked to original sources
PubMed1992

The structure determination of Sindbis virus core protein using isomorphous replacement and molecular replacement averaging between two crystal forms.

The structure of Sindbis virus core protein has been determined by a combination of multiple isomorphous replacement and molecular replacement averaging techniques. The multiple isomorphous replacement phase determinations were made for two crystal forms (P2(1) and P4(3)2(1)2) of the core protein. The real-space molecular replacement averaging was subsequently carried out between two copies of the protein per asymmetric unit in the monoclinic form and one copy in the tetragonal form. This greatly improved the quality of the electron density maps. The Sindbis virus core protein polypeptide could be traced and related to the known amino acid sequence. The averaging procedure between different crystal forms, as described in this paper, should be generally applicable to other systems.

Crystallization↗
PubMed1992

Acute and persistent effects of methamphetamine on developing monoaminergic neurons in reaggregate tissue culture.

Three-dimensional, rotation-mediated reaggregate tissue cultures composed of rostral mesencephalic cells and corpus striatal cells were used to examine the short-term and persistent effects of methamphetamine on developing monoamine-containing neurons. Reaggregates were exposed to drug for one week. Reductions in reaggregate endogenous dopamine and serotonin levels occurred following treatment with methamphetamine during days 15-22 of culture over the concentration range 10(-7) to 10(-4) M. The highest methamphetamine concentration reduced dopamine and serotonin levels to 29 and 33%, respectively, of control values. Monoamine levels were reduced from control values after 3 days of exposure to 10(-4) M methamphetamine. No further reduction resulted from 4 additional days of drug treatment. In order to determine whether monoaminergic neurons would recover from the drug-induced deficit, reaggregates were exposed to 10(-4) M methamphetamine for 7 days and then grown in drug-free media for an additional 20 days. During the 20 day recovery period, monoamine levels in the control group increased with time in culture. After an initial rapid increase (recovery days 0-9), the level of monoamines in the recovery group remained at a constant proportion to the level in the control group suggesting that the monoaminergic neurons return to a rate of development similar to that seen in untreated cultures. However, this rate was not sufficient to overcome the reduction in monoamine levels produced by 7 days of methamphetamine treatment. The results indicate that the effects of methamphetamine on developing monoaminergic neurons are marked and persistent.

Animals↗
PubMed1992

Processing of structural polypeptides of infectious flacherie virus of the silkworm, Bombyx mori: VP1 and VP4 are derived from VP0.

Infectious flacherie virus of the silkworm, Bombyx mori, contains five major polypeptides termed VP0, VP1, VP2, VP3, and VP4 in the order of descending molecular weight. Immunoblot analysis with specific antisera against each of these structural polypeptides showed that antisera against VP1 and VP4 unequivocally reacted with VP0 as well as their homologous structural polypeptides. Limited proteolysis of VP0 and VP1 by Staphylococcus aureus V8 protease gave several common polypeptide fragments. Amino acid sequence analysis showed that VP0 and VP4 shared a common NH2-terminal amino acid sequence. These results indicate that VP1 and VP4 are generated from VP0 and that VP4 occupies the NH2-terminal portion of VP0.

Amino Acid Sequence↗
PubMed1992

Clinical value of scrotopenogram for evaluating varicocele and erectile dysfunction.

While there is as yet no established theory regarding a possible relationship between varicocele and erectile failure, it is not uncommon to encounter those cases in which two conditions coexist clinically. We describe a new technique to identify these two conditions by a single injection of radioisotope. In scrotopenogram, varicocele is diagnosed by comparing the radioactivity in each hemiscrotum during the five minutes after injection of radioisotope. Then, after the patient is exposed to audiovisual sexual stimulation, the dynamic penile flow is measured for the next thirty minutes. We evaluated 185 impotent patients and 9 patients with varicocele. In the 185 erectile failure patients, varicoceles were also present in 33 (17.8%). In the 9 patients who presented themselves chiefly with varicoceles, 3 (33.3%) also had erectile failure. Thus, in 194 patients 36 (18.5%) cases of combined conditions were identified by the scrotopenogram technique. We believe this new technique could be an alternative method for noninvasively examining impotent patients with varicoceles.

Adult↗
PubMed1991

Structure of Sindbis virus core protein reveals a chymotrypsin-like serine proteinase and the organization of the virion.

Sindbis virus consists of a nucleocapsid core surrounded by a lipid membrane through which penetrate 80 glycoprotein trimers. The structure of the core protein comprising the coat surrounding the genomic RNA has been determined. The polypeptide fold from residue 114 to residue 264 is homologous to that of chymotrypsin-like serine proteinases with catalytic residues His 141, Asp 163 and Ser 215 of the core protein positioned as in other serine proteinases. The C-terminal tryptophan remains in the P1 substrate site subsequent to the autocatalytic cis cleavage of the capsid protein, thus rendering the proteinase inactive. Model building of the Sindbis core protein dimer shows that the nucleocapsid is likely to have T = 4 quasisymmetry.

Amino Acid Sequence↗
PubMed1991

Immortalization of embryonic mesencephalic dopaminergic neurons by somatic cell fusion.

To facilitate the study of trophic interactions between mesencephalic dopaminergic neurons and their target cells, clonal hybrid cell lines have been developed from rostral mesencephalic tegmentum (RMT) of the 14-day-old embryonic mouse employing somatic cell fusion techniques. Among the hybrid cell lines obtained, one contains a high level of dopamine (DA), another predominantly 3,4-dihydroxyphenylalanine (DOPA), and a third no detectable catecholamines. The hybrid nature of the cell lines is supported by karyotype analysis and by the expression of adhesion molecules as assessed by aggregation in rotation-mediated cell culture. The DA cell line shows neuronal properties including catecholamine-specific histofluorescence, neurite formation with immunoreactivity to neurofilament proteins, and large voltage-sensitive sodium currents with the generation of action potentials. In contrast to the pheochromocytoma cell line (PC12), the dopamine content of the DA hybrid cell line is depleted by low concentrations of N-methyl-4-phenylpyridinium ion (MPP+), the active metabolite of the neurotoxin N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).

1-Methyl-4-phenylpyridinium↗
PubMed1991

Some general influences of n-decylmethyl sulfoxide on the permeation of drugs across hairless mouse skin.

The influences of n-decylmethyl sulfoxide (NDMS) on the permeation of phenyl propanolamine, propranolol, acyclovir, and hydrocortisone through hairless mouse skin were investigated. Permeation of these compounds increased systematically with increasing NDMS concentration up to a limiting value for the permeability coefficient of about 0.1 cm/h. Permeability coefficients obtained with stripped skin indicated that, where NDMS has its maximal effect, the compounds diffuse through the skin as if there were no stratum corneum. Diffusion lag times of the test compounds through skin sections exposed to NDMS were far shorter than lag times in control experiments. The kinetics of NDMS action were assessed by pretreating skin sections for various periods of time with the enhancer and then assessing permeability. When applied as a 10 mM aqueous solution, the full effect of NDMS was obtained in 3 h of exposure and the effect lasted for at least 24 h. Treating the skin with ethanol/water (2:1) to elute NDMS after the pretreatment did not diminish its effect. Propranolol and phenyl propanolamine solubilized NDMS, presumably through the formation of mixed micelles, which had a profound effect on the permeation rates of both drug and enhancer.

Acyclovir↗
PubMed1991

Mechanisms of ionophore-induced stimulation of renin secretion with special reference to a chemiosmotic hypothesis.

The effects of several ionophores on renin secretion were investigated in rabbit renal cortical slices. When slices were incubated in the absence of Ca++, the K+ ionophore valinomycin (10(-5) approximately 5 x 10(-4) M) or the monovalent cation ionophore nonactin (10(-4) M) stimulated renin secretion about 2-fold. The renin secretion stimulated by valinomycin was further increased by inclusion of the H+ ionophore, carbonylcyanide m-chlorophenylhydrazone. The electroneutral K+/H+ exchange ionophore nigericin (10(-5) approximately 5 x 10(-4) M) stimulated renin secretion in a dose-dependent manner, producing a maximal stimulation of about 17-fold. Another electroneutral exchange ionophore, monensin, also significantly stimulated secretion. The stimulation by both valinomycin and nigericin was apparent whether slices were incubated in Na(+)-rich or K(+)-rich media. The extent of stimulation by the two ionophores was dependent upon the presence of anion with acetate greater than Cl greater than isethionate greater than thiocyanate. Thiocyanate itself markedly inhibited renin secretion. Incubating of slices in an iso-osmotic ammonium acetate medium which is known to induce rapid swelling of secretory granules, stimulated renin secretion to the magnitude comparable to that of maximal stimulation by nigericin in a potassium acetate medium. The pattern of response to these ionophores indicates that changes in K+, H+ and anion gradients across the renin secretory granule may modulate renin secretory rate. It is proposed that conditions which allow accumulation of K+ and anion within acidic renin secretory granules lead to osmotic swelling of the granules and that granule swelling may promote exocytosis.

Animals↗
PubMed1990

Erotic erection versus nocturnal erection.

To clarify the correlation between erotic and nocturnal erections, and to evaluate the diagnostic efficacy of the audiovisual stimulation penogram as an initial screening test for impotent patients, a comparative study of 137 impotent patients was designed. The audiovisual stimulation penogram shows dynamic penile blood flow change during audiovisual stimulation using a radioisotope (99mtechnetium) and is classified as type 1--similar findings to normal volunteers, type 2A--impossible erection due to insufficient blood flow, type 2B--unstable erection due to severe fluctuation in blood flow and type 2C--delayed erection. The compatibility ratios of the audiovisual stimulation penogram types 1, 2A and 2C with some tests for nocturnal erection were relatively high (63 to 80%) and when compared to the final diagnosis all but 1 of the compatible cases with nocturnal erection studies were able to be diagnosed correctly. However, the compatibility ratio of the audiovisual stimulation penogram type 2B was markedly low (35%) and this group had complicated etiologies, including many more psychogenic than organic causes. Although the mechanisms of the erotic and nocturnal erections have not been fully elucidated to date, our results suggest that the audiovisual stimulation penogram seems to be an appropriate initial screening step if we refine the criteria for type 2B, and a comprehensive interpretation of the tests for erotic and nocturnal erections will result in a more accurate diagnosis.

Erectile Dysfunction↗
PubMed1990

Transdermal delivery of bioactive peptides: the effect of n-decylmethyl sulfoxide, pH, and inhibitors on enkephalin metabolism and transport.

We investigated the effects of the nonionic surfactant, n-decylmethyl sulfoxide (NDMS), pH, and inhibitors on the metabolism and the permeation of amino acids, dipeptides, and the pentapeptide enkephalin, through hairless mouse skin. An HPLC gradient method was developed to identify the possible peptide and amino acid metabolites of leucine-enkephalin. NDMS increased the permeability of all amino acids and peptides tested. At neural pH, the enzyme activity within the skin was such that no flux of leucine-enkephalin (YGGFL) was observed and the donor cell concentration of YGGFL decreased rapidly. The major cleavage occurred at the Tyr-Gly bond. At pH 5.0 the metabolic activity was reduced significantly and a substantial flux of YGGFL was observed. Enzymatically stable YGGFL analogues, Tyr-D-Ala-Gly-Phe-Leu (YDAGFL) and its amide, exhibited significant fluxes even at neutral pH in the presence of NDMS, but with substantial metabolism. YDAGFL amide was more stable to metabolism than YDAGFL. The rates of metabolism of the peptides in the skin homogenates were in the order: FL much greater than YGGFL greater than GFL greater than GGFL much greater than YG, YGG much greater than YDAGFL amide. In the skin homogenates puromycin and amastatin showed the highest inhibitory effects, while FL and GFL were only slightly active. However, in the skin diffusion experiments, FL allowed the highest amount of intact parent compound to permeate, making it the most potent inhibitor. These results show that the complex proteolytic enzyme activities occurring during skin permeation are different from those in skin homogenates and that a combination of enhancer, pH adjustment, and inhibitors can increase the transdermal delivery of peptides.

Administration, Cutaneous↗
PubMed1989

Functional analysis of the 3' control region of the potato wound-inducible proteinase inhibitor II gene.

Proteinase inhibitor genes are expressed strongly in specific plant tissues under both developmental and environmental regulation. We have studied the role of the 3' control region of the potato proteinase inhibitor II gene (PI-II) that is inducible in leaves in response to herbivore attacks or other severe wounding. Comparison of the terminator from the PI-II gene with two different terminators from the 6b and 7 genes, driven by a common PI-II promoter-cat fusion molecule, indicated that the PI-II terminator provided the most efficient expression of cat. The PI-II terminator also caused a significantly elevated cat gene expression driven by the cauliflower mosaic virus 35S promoter. The increase in the level of expression is probably not due to the presence of an enhancer element in the PI-II terminator region, but to cis-acting elements involved in mRNA processing or stability. Both transient and stable transformation analyses of the deletion mutants in the 3'-flanking sequence indicated that about a 100-base pair DNA fragment surrounding the polyadenylation site is essential for the efficient gene expression. This region seems to consist of several regulatory elements, including the conserved sequence, CGTGTCTT, which is located 9 bases downstream from the polyadenylation site. The elements appear to contribute to the increased stability of mRNAs containing the PI-II terminator.

Amino Acid Sequence↗
PubMed1989

Adult Wilms' tumor--a case report.

A case of Wilms' tumor in a 67 year-old female is presented. The tumor totally replaced the left kidney with extension to Gerota's fascia, the adrenal gland and ureter, with tumor thrombi in the left renal vein. Multiple bony metastases to the skull, shoulder, rib, ilium, acetabulum and femur were noted also. Microscopically, the tumor was composed predominantly of blastemal tissue with diffuse anaplasia with areas of tubular differentiation and chondroid elements. Clear cell nests were found in the proximal ureter with gradual maturation downward.

Aged↗
PubMed1989

A case of urethral replacement with polytetrafluoro-ethylene graft for multiple anterior urethral strictures.

Recently, the authors had an opportunity to treat a 73-year-old male patient who was transferred to our institution with problematic multiple strictures of the anterior urethra subsequent to a suprapubic cystostomy. A proximal urethra was reconstructed with scrotal skin, but due to the shortage of distal skin, as a last resort we reconstructed a distal urethra using a polytetrafluoroethylene graft in place of 10 cm long urethral strictures. About 5 months after surgery, we had to reexplore the polytetrafluoroethylene graft area because of pain and found, much to our surprise, that the urethra had been completely regenerated around the length of polytetrafluoroethylene graft which now remained freely detached in the urethral canal. Following removal of the polytetrafluoroethylene graft, the patient could urinate normally and was subsequently discharged without further problems. We concluded that this case was incidentally successful with good regeneration of urethral mucosa of the anterior urethra by grafting a polytetrafluoroethylene tube.

Aged↗
PubMed1988

Reaction products of a new anti-cancer agent, Pt(IV)(cyclohexyldiamine)Cl4, with guanosine and 9-methylguanine: first crystal structures of Pt(cyclohexyldiamine) complexes with a nucleobase and a nucleoside.

Pt(IV)(dach)Cl4 (dach = cyclohexyldiamine) was reacted with guanosine and 9-methylguanine and their reaction products were analyzed by single-crystal x-ray diffraction. In both cases the resulting complexes, [Pt(dach)(guanosine)2]2+ and [Pt(dach)(9-methylguanine)2]2+ respectively, corresponded to an unanticipated reduction of the octahedral Pt(IV) starting material to a square planar Pt(II) species. The nature of the reducing agent is presently unknown.

Antineoplastic Agents↗