PubMed Health⌕ Search

Biomedical subjects

L Chung

Publications and source records attributed to L Chung.

26 records · Page 2Linked to original sources
PubMed1997

The core domain of the tissue transglutaminase Gh hydrolyzes GTP and ATP.

Tissue transglutaminase (TGase II) catalyzes the posttranslational modification of proteins by transamidation of available glutamine residues and is also a guanosinetriphosphatase (GTPase) and adenosinetriphosphatase (ATPase). Based on its homology with factor XIIIA, an extracellular transglutaminase, the structure of TGase II is likely composed of an N-terminal beta-sandwich domain, an alpha/beta catalytic core, and two C-terminally located beta-barrels. Here we used a domain-deletion approach to identify the GTP and ATP hydrolytic domains of TGase II. Full-length TGase II and two domain-deletion mutants, one retaining the N-terminal beta-sandwich and core domains (betaSCore) and the other retaining only the core domain, were expressed as glutathione S-transferase (GST) fusion proteins and purified. GST-Full and GST-betaSCore exhibited calcium-dependent TGase activity, whereas GST-Core had no detectable TGase activity, indicating the beta-sandwich domain is required for TGase activity but the C-terminal beta-barrels are not. All three GST-TGase II fusion proteins were photoaffinity-labeled with [alpha-32P]-8-azidoGTP and were able to bind GTP-agarose. The GTPase activity of GST-betaSCore was equivalent to that of GST-Full, whereas the ATPase activity was approximately 40% higher than GST-Full. GST-Core had approximately 50% higher GTPase activity and approximately 75% higher ATPase activity than GST-Full. The GTPase and ATPase activities of each of the GST-TGase II fusion proteins were inhibited in a dose-dependent manner by both GTPgammaS and ATPgammaS. These results demonstrate that the GTP and ATP hydrolysis sites are localized within the core domain of TGase II and that neither the N-terminal beta-sandwich domain nor the C-terminal beta-barrels are required for either GTP or ATP hydrolysis. Taken together with previous work [Singh, U. S., Erickson, J. W., & Cerione, R. A. (1995) Biochemistry 34, 15863-15871; Lai, T.-S., Slaughter, T. F., Koropchak, C. M., Haroon, Z. A., & Greenberg, C. S. (1996) J. Biol. Chem. 271, 31191-31195] the results of this study indicate that the GTP and ATP hydrolysis sites are localized to a 5. 5 kDa (47 amino acid) region at the start of the core domain.

Adenosine Triphosphatases↗
PubMed1997

Effect of DNA on the inactivation of O6-alkylguanine-DNA alkyltransferase by 9-substituted O6-benzylguanine derivatives.

Studies were carried out on the inactivation of pure human O6-alkylguanine-DNA alkyltransferase by 9-substituted O6-benzylguanine derivatives in the presence and absence of DNA. The addition of DNA increased the rate of inactivation of the alkyltransferase by O6-benzylguanine and its 9-methyl derivative but had little effect on the rate of inactivation by the 9-cyanomethyl derivative. In contrast, when O6-benzylguanine derivatives with larger 9-substituents such as ribose, 2'-deoxyribose, dihydrotestosterone, or 2-hydroxy-3-(isopropoxy)propyl were used, the addition of DNA was strongly inhibitory to the inactivation. In the case of O6-benzylguanine, O6-benzylguanosine, and O6-benzyl-2'-deoxyguanosine, these results were confirmed by directly measuring the rate of formation by the alkyltransferase of guanine, guanosine, or 2'-deoxyguanosine, respectively. The data indicated that the presence of DNA activated the alkyltransferase, rendering it more reactive with O6-benzylguanine or O6-benzyl-9-methylguanine, but that DNA interferes with the binding of inhibitors with larger 9-substituents, presumably by competing for the same binding site. Since these inactivators readily inactivate alkyltransferase in cells, the amount of cellular alkyltransferase bound to DNA must be small or readily exchangeable with the free form.

Animals↗
PubMed1994

The effect of using a pre-brushing mouthwash (Plax) on removal of tooth stain in vivo and in vitro.

The aim of this study was to determine whether the use of a pre-brushing mouthwash Plax reduced extrinsic tooth-staining in vivo and in vitro. Firstly, in a double-blind placebo controlled cross-over study, 20 subjects with tooth staining used Plax or a placebo for 14-day periods separated by a 1-month wash-out period. The area of stain was assessed before and after each mouthwash had been used from clinical photographs. Secondly, extracted 3rd molar teeth were stained with tea and chlorhexidine. After exposure to either Plax or placebo, the teeth were brushed in a standardized manner. The area and intensity of stain were assessed before and after rinsing and brushing. Results of the study in vivo showed that the mean % stained area for any of the surfaces studied changed very little throughout the study. No statistically significant changes were detected (Student t-test, p > 0.05). Results of the study in vitro showed that the mean area of stain fell by 19% after exposure to Plax and by 17% after exposure to placebo. No statistically significant changes were detected (Student t-test, p > 0.05). There were also no significant changes in intensity (Wilcoxon signed rank sum test p > 0.1).

Adult↗
PubMed1992

The effect of using a pre-brushing mouthwash (Plax) on oral hygiene in man.

The aim of this study was to investigate whether the use of a pre-brushing mouthwash (Plax) improved subjects' oral hygiene over a 2-week period. In a double-blind placebo controlled cross-over study, 33 adult subjects (mean age 35.3 years) used either Plax or a placebo mouthwash for 30 s prior to toothbrushing during a 2-week period. After a washout period of 4 weeks, the subjects used the other mouthwash in the same way. The modified plaque index of Quigley and Hein (QHI) was recorded for 16 teeth (16, 14, 13, 11, 21, 23, 24, 26, 36, 34, 33, 31, 41, 43, 44, 46) at each visit. The bleeding index (BI) was recorded at the beginning and end of the study. Results were analysed using a paired one-tailed t-test. Neither plax nor placebo mouthwashes reduced plaque scores significantly (p > 0.05) below baseline. There was no statistically significant difference between the mean BI at the beginning of the trial (0.42) and at the end (0.44). These results suggest that the routine use of Plax is not a useful adjunct to toothbrushing.

Aged↗
PubMed1988

Molecular evolution of the human immunodeficiency and related viruses.

A phylogenetic tree for different human immunodeficiency viruses type 1 (HIV1) and type 2 (HIV2), lentiviruses, and oncoviruses has been constructed by comparing the nucleotide sequences of the two regions of their pol genes that encode the reverse transcriptase and endonuclease/integrase. The analysis indicates that (1) different HIV1 strains form one cluster and their common ancestor diverged from the ancestor of HIV2, (2) the common ancestor of the HIV1 and HIV2 strains diverged from that of the lentivirus, and (3) the common ancestor of the lentivirus group and that of the oncoviruses diverged earlier than that. Divergence between the HIV1 and HIV2 strains seems to have occurred greater than 200 years ago, implying that AIDS has existed for a long time but went undetected. Furthermore, nonsynonymous changes are occurring uniformly through time, whereas synonymous changes are more variable among different lineages.

Base Sequence↗
PubMed1985

Interaction of gentamicin and spermine with bilayer membranes containing negatively charged phospholipids.

We measured the electrophoretic mobility of multilamellar phospholipid vesicles, the 31P NMR spectra of both sonicated and multilamellar vesicles, and the conductance of planar bilayer membranes to study the binding of spermine and gentamicin to membranes. Spermine and gentamicin do not bind significantly to the zwitterionic lipid phosphatidylcholine. We measured the concentrations of gentamicin and spermine that reverse the charge on vesicles formed from a mixture of phosphatidylcholine and either phosphatidylserine or phosphatidylinositol. From these measurements, we determined that the intrinsic association constants of the cations with these negative lipids are all about 10 M-1. This value is orders of magnitude lower than the apparent binding constants reported in the literature by other groups because the negative electrostatic surface potential of the membranes and the resultant accumulation of these cations in the aqueous diffuse double layer adjacent to the membranes have not been explicitly considered in previous studies. Our main conclusion is that the Gouy-Chapman-Stern theory of the aqueous diffuse double layer can describe surprisingly well the interaction of gentamicin and spermine with bilayer membranes formed in a 0.1 M NaCl solution if the negative phospholipids constitute less than 50% of the membrane. Thus, the theory should be useful for describing the interactions of these cations with the bilayer component of biological membranes, which typically contain less than 50% negative lipids. For example, our results support the suggestion of Sastrasinh et al. [Sastrasinh, M., Krauss, T. C., Weinberg, J. M., & Humes, H. D. (1982) J. Pharmacol. Exp. Ther. 222, 350-358] that phosphatidylinositol is the major binding site for gentamicin in renal brush border membranes.

Electric Conductivity↗
PubMed1971

Coordinative binding of divalent cations with ligands related to bacterial spores. Equilibrium studies.

It has been repeatedly postulated that the high heat resistance of bacterial spores is due to stabilization of biopolymers in the spore interior by a solid deposit of protective cement consisting of coordination complexes of ligands with divalent metal ions. This report presents data on metal-binding characteristics of some of the ligands related to spores as determined by means of potentiometric equilibrium measurements under conditions of temperature and ionic strength (t = 25.0 degrees C; mu = 1.0 KNO(3)) identical with those reported earlier by the authors in order to facilitate correlation by using comparable data. The spore ligands investigated in this study included 2,6-pyridinedicarboxylic acid (DPA), alpha,epsilon-diaminopimelic acid, D-glutamic acid, and D-alanine in a ratio of 1:1 with metal ions which are known to play a role in heat resistance of spores. Stability constants of the chelates of these spore ligands with metal ions such as Ca(II), Mg(II), Cu(II), Ni(II), Zn(II), Co(II), and Mn(II) have been determined. In general the metal chelates of DPA exhibited the greatest stability. On the basis of a consideration of the stability data together with the known configurations of the ligand and the coordination requirements of the metal ions, possible structures indicating the coordinate binding of the spore ligands with the metal ions are presented. All the metal chelates except those of Ca(II) were found to undergo hydrolysis and separation of solid phase in the pH range 7-8.5. The relatively greater hydrolytic stability of Ca(II) chelates and the high affinity of DPA for metal ions appear to be of biological significance insofar as these two spore components are more widely associated with the heat resistance of bacterial spores.

Alanine↗