Biomedical subjects

D G Chung

Publications and source records attributed to D G Chung.

15 recordsLinked to original sources

PubMed1995

Follistatin concentrations in follicular fluid of normal and polycystic ovaries.

Follistatin (FS) is an activin/inhibin binding protein which is believed to act in an autocrine/paracrine manner to regulate growth and differentiation. Although FS has been identified in human follicular fluid, it remains unclear how its concentration changes during selection and atresia, and what the concentrations of FS are in follicles of women with polycystic ovary syndrome (PCOS). Towards this goal, we have measured by radioimmunoassay the concentrations of FS in follicular fluid obtained from dominant and atretic cohort follicles of normal cycling women, preovulatory follicles of in-vitro fertilization (IVF) patients, and small Graafian follicles of patients with PCOS. In all cases, the follicular fluid concentration of FS was much higher (approximately 100-fold) than that reported in serum. The FS concentrations (ng/ml) were 203 +/- 42 (normal dominant), 185 +/- 17 (atretic cohort), 185 +/- 5 (IVF), and 250 +/- 14 (PCOS). There was no statistical difference between these mean values of FS. Further, there were no significant correlations between the follicular fluid concentrations of FS and the concentrations of oestradiol, progesterone, or androstenedione. These results indicate that human Graafian follicles, regardless of whether they are healthy or atretic, normal or PCOS, contain high steady-state concentrations of FS in the micro-environment. Collectively, these data fit with the hypothesis that major increases and decreases in the concentration of FS in the micro-environment may not play a key role in the mechanisms of selection, atresia, and PCOS in women. The possibility of regulation of intrinsic activin and inhibin activity through FS binding is discussed.

Case-Control Studies↗

PubMed1994

Endodermal sinus tumor arising from a dysgenetic gonad in a 46,XX female combined with müllerian agenesis.

The occurrence of neoplastic transformation in a dysgenetic gonad of a female with 46,XX karyotype is very rare. Moreover, to our knowledge, a case of endodermal sinus tumor arising from that setting combined with Müllerian agenesis has not been reported. This case suggests the possibility of development of cancer in a dysgenetic ovary of a female even with 46,XX or Müllerian agenesis.

Adult↗

PubMed1994

SPECT for differential diagnosis of dementia and correlation of rCBF with cognitive impairment.

99mTc-HM-PAO single photon emission computed tomography (SPECT) was used to image 30 patients referred for the assessment of dementia. SPECT images revealed various patterns of regional cerebral perfusion (rCBF) in the subgroups of patients with the clinical diagnoses of Alzheimer's disease (AD, n = 14), Pick's disease (n = 1), and multi-infarct dementia (n = 7). In three patients, SPECT clarified the clinical differential diagnostic possibilities. Using a relative rCBF quantification technique, the relationship between specific cognitive impairments and rCBF in the AD patients was determined. There was a significant correlation between language impairment and left hemisphere hypoperfusion, whereas, apraxia correlated with hypoperfusion in the left parietal region. Thus, HM-PAO SPECT is useful as an aid in the differential diagnosis of dementia and the technique of relative rCBF quantification with SPECT may contribute to the understanding of the clinico-anatomical relations of cognitive deficits in dementia.

Aged↗

PubMed1994

Technetium-99m-HMPAO SPECT, CT and MRI in the evaluation of patients with chronic traumatic brain injury: a correlation with neuropsychological performance.

UNLABELLED: The purposes of this study were: (1) to compare 99mTc-hexamethylpropyleneamineoxime (HMPAO) SPECT with CT and MRI in chronic traumatic brain injury (TBI) patients and (2) to correlate both functional and structural neuroimaging measurements of brain damage with neuropsychological (NP) performance. METHODS: Twenty-nine patients (minor TBI, n = 15 and major TBI, n = 14) and 17 normal controls (NC) underwent HMPAO SPECT, CT, MRI and NP testing. Imaging data were analyzed both visually and quantitatively. RESULTS: Nineteen (66%) patients showed 42 abnormalities on SPECT images, whereas 13 (45%) and 10 (34%) patients showed 29 abnormalities on MRI and 24 abnormalities on CT. SPECT detected relatively more abnormalities than CT or MRI in the minor TBI subgroup. The TBI group showed impairment on 11 tests for memory, attention and executive function. Of these, the anterior-posterior ratio (APR) correlated with six tests, whereas the ventricle-to-brain ratio (VBR), a known structural index of a poor NP outcome, correlated with only two tests. CONCLUSION: In evaluating chronic TBI patients, HMPAO SPECT, as a complement to CT or MRI, may play a useful role by demonstrating brain dysfunction in morphologically intact brain regions and providing objective evidence for some of the impaired NP performance.

Adult↗

PubMed1992

Neuroanatomical localization for clinical SPECT perfusion brain imaging: a practical proportional grid method.

For the purpose of facilitating anatomical localization in interpretation of 99Tcm-hexamethylpropyleneamine oxime (HMPAO) brain single photon emission tomographic (SPECT) scans, a stereotaxic proportional grid system was applied in the form of an interactive computer program. This method takes advantage of a rotating gamma camera system which permits planar scout imaging for the determination of anatomical reference lines, and standardization of tomographic slices for brain size. Using measurements made on a lateral planar HMPAO image, proportional grids were constructed onto standardized transaxial images. This method was implemented for 33 clinical HMPAO SPECT studies. It required less than 15 min of an operator's time. This simple and practical neuroanatomical localization technique can be instrumental as an aid to the interpretation of routine clinical HMPAO SPECT images.

Adult↗

PubMed1992

Assessment of regional cerebral perfusion by 99Tcm-HMPAO SPECT in chronic fatigue syndrome.

Chronic fatigue syndrome (CFS) is a severely disabling illness of uncertain aetiology. It is characterized by a chronic, sustained or fluctuating sense of debilitating fatigue without any other known underlying medical conditions. It is also associated with both somatic and neuropsychological symptoms. Both physical and laboratory findings are usually unremarkable. Regional cerebral blood flow (rCBF) was assessed in 60 clinically defined CFS patients and 14 normal control (NC) subjects using 99Tcm-hexamethylpropyleneamine oxime (99Tcm-HMPAO) single photon emission computed tomography (SPECT). Compared with the NC group, the CFS group showed significantly lower cortical/cerebellar rCBF ratios, throughout multiple brain regions (P < 0.05). Forty-eight CFS subjects (80%) showed at least one or more rCBF ratios significantly less than normal values. The major cerebral regions involved were frontal (38 cases, 63%), temporal (21 cases, 35%), parietal (32 cases, 53%) and occipital lobes (23 cases, 38%). The rCBF ratios of basal ganglia (24 cases, 40%) were also reduced. 99Tcm-HMPAO brain SPECT provided objective evidence for functional impairment of the brain in the majority of the CFS subjects. The findings may not be diagnostic of CFS but 99Tcm-HMPAO SPECT may play an important role in clarifying the pathoaetiology of CFS. Further studies are warranted.

Adolescent↗

PubMed1992

Technetium-99m-HMPAO SPECT in the evaluation of patients with a remote history of traumatic brain injury: a comparison with x-ray computed tomography.

The functional imaging modality has potential for demonstrating parenchymal abnormalities not detectable by traditional morphological imaging. Fifty-three patients with a remote history of traumatic brain injury (TBI) were studied with SPECT using 99mTc-hexamethylpropyleneamineoxime (HMPAO) and x-ray computed tomography (CT). Overall, 42 patients (80%) showed regional cerebral blood flow (rCBF) deficits by HMPAO SPECT, whereas 29 patients (55%) showed morphological abnormalities by CT. Out of 20 patients with minor head injury, 12 patients (60%) showed rCBF deficits and 5 patients (25%) showed CT abnormalities. Of 33 patients with major head injury, 30 patients (90%) showed rCBF deficits and 24 patients (72%) showed CT abnormalities. Thus, HMPAO SPECT was more sensitive than CT in detecting abnormalities in patients with a history of TBI, particularly in the minor head injury group. In the major head injury group, three patients showed localized cortical atrophy by CT and normal rCBF by HMPAO SPECT. In the evaluation of TBI patients, HMPAO SPECT is a useful technique to demonstrate regional brain dysfunction in the presence of morphological integrity as assessed by CT.

Adult↗

PubMed1991

Cloning, sequencing and overexpression of the gene for prokaryotic factor EF-P involved in peptide bond synthesis.

A soluble protein EF-P (elongation factor P) from Escherichia coli has been purified and shown to stimulate efficient translation and peptide-bond synthesis on native or reconstituted 70S ribosomes in vitro. Based on the partial amino acid sequence of EF-P, 18- and 24-nucleotide DNA probes were synthesized and used to screen lambda phage clones from the Kohara Gene Bank. The entire EF-P gene was detected on lambda clone #650 which contains sequences from the 94 minute region of the E.coli genome. Two DNA fragments, 3.0 and 0.78 kilobases in length encompassing the gene, were isolated and cloned into pUC18 and pUC19. Partially purified extracts from cells transformed with these plasmids overrepresented a protein which co-migrates with EF-P upon SDS polyacrylamide gel electrophoresis, and also exhibited increased EF-P mediated peptide-bond synthetic activity. Based on DNA sequence analysis of this gene, the EF-P protein consists of 187 amino acids with a calculated molecular weight of 20,447. The sequence and chromosomal location of EF-P establishes it as a unique gene product.

Amino Acid Sequence↗

PubMed1991

A proposed role for IF-3 and EF-T in maintaining the specificity of prokaryotic initiation complex formation.

Initiation factor-free 30S subunits of E. coli ribosomes bind aminoacyl-tRNAs more efficiently than fMet-tRNA(fMet). Elongator-tRNA binding was unaffected by IF-1 or IF-2 but was inhibited by IF-3. Their combination reduced this binding up to 40% and stimulated that of fMet-tRNA(fMet). Unexpectedly, EF-T also prevented elongator-tRNA binding by complexing both to the 30S and to the aminoacyl-tRNAs. Using AUGU3 as mRNA, elongator-tRNAs competed with fMet-fRNA(fMet) and with tRNA(fMet), fMet-tRNA(fMet) reacted with puromycin after addition of 50S subunits suggesting that it occupied the P site. EF-T directed binding of phe-tRNA to the 30S.AUGU3 complex at the A site only if fMet-tRNA(fMet) or tRNA(fMet) filled the P/E site. We propose that one function of EF-T may be to prevent the entry of aminoacyl-tRNAs into the 30S particle during initiation. The possibility that a special site for fMet-tRNA resides on 16S rRNA is also discussed.

Binding Sites↗

PubMed1989

Regulation of gene expression at the translational level. The rescue factor reverses thermosensitive protein synthesis in N4316, a conditionally-lethal mutant of Escherichia coli defective in translation.

Extracts of the conditionally-lethal mutant Escherichia coli N4316 are defective in a newly described translation factor, the rescue protein. We have analyzed the in vitro translation products of this mutant by gel electrophoresis during normal and arrested synthesis at the permissive and non-permissive temperatures. Translation programmed with MS2 bacteriophage RNA at the non-permissive temperature results in highly reduced synthesis of the coat protein with no detectable levels of the maturation and replicase products. Thus the relative number of copies of proteins synthesized by the ribosomes is altered in this mutant. In addition, there is mistranslation of the coat gene which results in the overproduction of the phage encoded no. 7 protein. Aberrant synthesis is also reflected in the increased read-through of termination codons during synthesis directed by phage RNAs harbouring amber mutations in the coat cistron. The rescue protein, purified from the parental strain, is able to complement the thermosensitive defect and restore proper synthesis. Biochemical characterization of the defect in the absence of rescue shows no detectable deficiency in the extent of initiation complex formation in reactions inhibited with sparsomycin. Peptidyltransferase is fully active as judged by the kinetics of formylmethionine-puromycin formation. However, rescue does exert an effect at the level of termination. In addition, the thermolability of the mutant can be reversed by dissociating 70S ribosomes into 30S and 50S subunits. Based on these and other observations, we propose tht rescue mediates a novel function in the association/dissociation of ribosomal subunits which is essential to the accuracy and efficiency of translation.

Bacterial Proteins↗

PubMed1987

Recognition of translational termination signals.

Ribosomes can specifically shift at certain codons so that the mRNA is read in two different reading frames. To determine if frameshifting occurs at the level of termination, polymers of defined sequence containing AUG, a coding sequence and an in- or out-of-phase nonsense codon were used to bind a termination substrate or to program synthesis and release of dipeptides in a highly purified in vitro translation system. fMet-tRNA bound to ribosomes with AUGUAA, AUGUAAn, AUGUUU, AUGUUA or AUGUAn was not a substrate for release factor RF-1. In contrast, AUGU1UAA, AUGU3UAAn, AUGU4UAAn, AUGU5UAAn effected RF-1-dependent release of fMet from ribosomes. This suggests that nonsense codons can stimulate release whether they occur in- or out-of-phase. Addition of exogenous UAA and RF-1 stimulated release with all oligonucleotides tested. Propagation restricted the RF-1-dependent recognition of out-of-phase nonsense codons but did not restrict recognition of in-phase UAA in AUGU3UAAn. Release of dipeptides from ribosomes programmed with AUGU4UAAn occurred without EF-G and with a mutant lacking EF-G activity, suggesting that out-of-phase termination can occur prior to translocation outside the ribosomal A-site. We propose that the ribosome X RF complex is required to complete proteins, but is also able to frameshift at a nonsense codon resulting in occasional out-of-phase termination of protein synthesis.

Codon↗

PubMed1987

Reconstruction of peptidyltransferase activity on 50S and 70S ribosomal particles by peptide fragments of protein L16.

Ribosomal protein L16 was digested with Staphylococcus aureus protease V8 and the resulting peptides were separated by reversed-phase high-performance liquid chromatography. One of the fragments, identified by sequence analysis as the N-terminal peptide of L16, was shown to exhibit partial peptide-bond-formation and transesterification activities of peptidyltransferase upon reconstitution with L16-depleted 50S core particles. However, several proteins enhanced these activities. L15 increased both reactions when added to the reconstitution mixture, suggesting a limited capacity of the L16 peptide to incorporate into 50S core particles. In contrast, the interaction of L11 with the N-terminal peptide stimulated the transesterification reaction but not the peptide-bond-forming activity of ribosomes, indicating a different topological domain for these reactions. Also, EF-P, a soluble protein which reconstructs the peptide-bond formation and transesterification reactions on 70S ribosomes, stimulated both peptidyltransferase activities exhibited by the L16 N-terminal peptide.

Acyltransferases↗

PubMed1986

Internal architecture of the core nucleosome: fluorescence energy transfer studies at methionine-84 of histone H4.

Chicken histone H4, labeled separately at Met-84 with N-[[(iodoacetyl)amino]ethyl]-5-naphthylamine-1-sulfonic acid and 5-(iodoacetamido)fluorescein, was reassociated with unlabeled histones H2A, H2B, and H3 and 146 base pairs of DNA to produce fluorescently labeled nucleosomes having physical characteristics virtually the same as those of native core particles. Four types of particles were prepared containing respectively unlabeled H4, dansylated H4, fluoresceinated H4, and a mixture of the two labeled H4 molecules. Quantitative singlet-singlet energy-transfer measurements were carried out to determine changes in the distance between the two Met-84 H4 sites within the same nucleosome following conformational transitions which we have reported earlier. In the ionic strength range 0.1-100 mM NaCl, the distance between these sites is less than 2 nm except at 1 mM. Between 100 and 600 mM monovalent salt the distance separating the donor and acceptor fluors at Met-84 H4 increases to 3.8 nm. The conformational change centered around 200 mM NaCl is cooperative. Our results and those of others indicate that there is little unfolding of the histone octamer, at least around Met-84 H4, in the entire ionic strength range studied. A mechanism involving the rotation of the globular portion of H4 is proposed to account for this transition which occurs at physiological ionic strengths.

Animals↗

PubMed1986

Intermolecular histone H4 interactions in core nucleosomes.

Chicken histone H4, labeled at methionine-84 with 1-N-pyrenyliodoacetamide, has been incorporated into a nucleosome-like particle with core length DNA and unmodified histones H2A, H2B, and H3. These synthetic nucleosomes exhibit properties very similar to those displayed by native particles and those labeled with other fluors. The emission spectrum of the pyrene-labeled nucleosome was characteristic of excited dimer (excimer) fluorescence, indicating that the single pyrene groups on the two H4 molecules are in close proximity in the reconstituted particle. Histone H4 was also labeled randomly at lysines with a group that contains two pyrene moieties separated by 12 A at most. Incorporation of this histone into nucleosome-like particles provides an excimer standard which does not depend on intermolecular interactions. The properties of the pyrene-containing nucleosome were examined as a function of ionic strength. It was found that the H4-H4 pyrene excimer fluorescence exhibited a cooperative disruption centered at 0.1 M NaCl which preceded increases in accessibility and environment polarity revealed by other fluors attached at the same site.

Animals↗

PubMed1985

Conformations of the core nucleosome: effects of ionic strength and high mobility group protein 14 and 17 binding on the fluorescence emission and polarization of dansylated methionine-84 of histone H4.

Chicken histone H4 labeled at Met-84 with the fluor N-[(acetylamino)ethyl]-8-naphthyl-amine-1-sulfonic acid has been incorporated into a nucleosome which has physical characteristics virtually identical with those of native core nucleosomes. The fluorescence emission and polarization properties of the labeled nucleosome were measured as a function of ionic strength and the binding of high mobility group (HMG) proteins 14 and 17. Also, the accessibility of the fluor to the quenching agent acrylamide was determined. It was found that the fluorescence emission changes in the range 0.1-1000 mM NaCl are rather small and indicate that no major unfolding of the octamer structure occurs around Met-84 on H4 at least. Five or perhaps six discrete states were found in that ionic strength range. Each has a different accessibility to the quenching agent. The range of accessibilities varied from 9 X 10(-7) to 32 X 10(-7) mol-1 s-1 for 0.1-1000 mM NaCl, respectively. Polarization measurements showed that there was little change in the rotational relaxation lifetime of the fluor at ionic strengths less than 50 mM NaCl. Above this value, the rotational relaxation lifetimes decreased from 107 to 25 ns at 600 mM NaCl, indicating a moderately increased rotational freedom for the fluor. It is suggested that the histone octamer changes its degree of compaction in the range 0.1-600 mM NaCl but that no major protein unfolding occurs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗