Biomedical subjects

S Kwong

Publications and source records attributed to S Kwong.

At least 19 recordsLinked to original sources

PubMed2001

Cancer incidence in the United Farmworkers of America (UFW), 1987-1997.

BACKGROUND: The purpose of this study was to evaluate cancer incidence in the membership a largely Hispanic farmworker labor union in California, the United Farmworkers of America (UFW) and to examine cancer-site specific distributions as well as histology and stage of cancer at diagnosis in this group. METHODS: An electronic record linkage was conducted between a membership roster of the UFW and the database of the California Cancer Registry, the population-based cancer registry in California for the years 1987-1997. Based upon the results of the linkage, morbidity odds ratios were calculated using the distribution of cancer in the California Hispanic population as the reference to determine if risk of specific cancers was higher or lower in the UFW. Time since first joining the union was evaluated, as was the proportional distribution of histologic subtypes and stage at diagnosis, again comparing the experience of the UFW membership to the California Hispanic population. RESULTS: Several types of cancer were elevated in the UFW membership in comparison to the California Hispanic population. Morbidity odds ratios and 95% confidence limits were elevated for leukemia (O.R. = 1.59: 95% C.I. = 1.07-2.37), stomach cancer (O.R. = 1.69: 95% C.I. = 1.24-2.27), uterine cervix cancer (O.R. = 1.63: 95% C.I. = 1.11-2.44) and uterine corpus cancer (O.R. = 1.68: 95% C.I. = 1.05-2.67). Brain cancer was also elevated although not significantly so (O.R. = 1.57: 95% C.I. = 0.96-2.53). CONCLUSIONS: Risk of leukemia, stomach, cervix and uterine cancers was elevated in California farmworkers. The histologic distribution of leukemia and brain cancers within the UFW membership did not differ from the distribution in the general California population although small numbers of cancers in the UFW hindered interpretation of these results. Members of the UFW experienced later stage of disease at diagnosis in comparison to California Hispanics for most major cancer sites but not for breast cancer.

Agricultural Workers' Diseases↗

PubMed2001

An information-based sequence distance and its application to whole mitochondrial genome phylogeny.

MOTIVATION: Traditional sequence distances require an alignment and therefore are not directly applicable to the problem of whole genome phylogeny where events such as rearrangements make full length alignments impossible. We present a sequence distance that works on unaligned sequences using the information theoretical concept of Kolmogorov complexity and a program to estimate this distance. RESULTS: We establish the mathematical foundations of our distance and illustrate its use by constructing a phylogeny of the Eutherian orders using complete unaligned mitochondrial genomes. This phylogeny is consistent with the commonly accepted one for the Eutherians. A second, larger mammalian dataset is also analyzed, yielding a phylogeny generally consistent with the commonly accepted one for the mammals. AVAILABILITY: The program to estimate our sequence distance, is available at http://www.cs.cityu.edu.hk/~cssamk/gencomp/GenCompress1.htm. The distance matrices used to generate our phylogenies are available at http://www.math.uwaterloo.ca/~mli/distance.html.

Animals↗

PubMed2000

Nonideality and the nucleation of sickle hemoglobin.

The homogeneous and heterogeneous nucleation kinetics of sickle hemoglobin (HbS) have been studied for various degrees of solution crowding by substitution of cross-linked hemoglobin A, amounting to 50% of the total hemoglobin. By cross-linking hemoglobin A, hybrid formation between hemoglobin A and hemoglobin S was prevented, thus simplifying the analysis of the results. Polymerization was induced by laser photolysis, and homogeneous nucleation kinetics were determined by observation of the stochastic behavior of the onset of light scattering. Heterogeneous nucleation was determined by observing the exponential growth of the progress curves, monitored by light scattering. At concentrations between 4 and 5 mM tetramer (i.e., approximately 30 g/dl), the substitution of 50% HbA for HbS slows the reaction by a factor of 10(3) to 10(4). Using scaled particle theory to account for the crowding of HbA, the observed decrease in the homogeneous nucleation rate was accurately predicted, with no variation of parameters required. Heterogeneous nucleation, on the other hand, is not well described in the present formulation, and the theory for this process appears to require modification of the way in which nonideality is introduced. Nonetheless, the accuracy of the homogeneous nucleation description suggests that such an approach may be useful for other assembly processes that occur in a crowded intracellular milieu.

Cross-Linking Reagents↗

PubMed1999

Changes in the functional properties of bovine hemoglobin induced by covalent modification with polyethylene glycol.

Polyethylene glycol conjugation to proteins and peptides (PEGylation) has been shown to promote increased retention time in the circulation as well as to blunt immune or allergic reactions. PEGylated bovine hemoglobin (PEG-Hb) is being explored in human clinical trials as an oxygen delivering agent for the sensitization of solid tumors to radiation therapy. In this study the functional properties of PEG-Hb were compared to those of bovine hemoglobin (Hb), the mutant human hemoglobin Rothchild and bovine hemoglobin crosslinked between the beta chains. The rate of heme transfer from Hb to serum albumin at pH 9.0 was greatly increased by PEGylation, suggesting destabilization of the heme-globin linkage and of the bonds between alpha beta dimers. Measurement of oxygen binding equilibrium showed that the oxygen affinity of Hb became unusually dependent on temperature and Hb concentration after PEGylation. Evidence is presented to suggest that PEGylation of lysine beta-81 at the entrance to the central cavity of the Hb tetramer might be responsible for these observations. The alterations of the functional properties of Hb induced by PEGylation are consistent with the beneficial effects of PEG-Hb in exchange transfusion and radiation sensitization models of human conditions.

Animals↗

PubMed1999

A Compression Algorithm for DNA Sequences and Its Applications in Genome Comparison.

We present a lossless compression algorithm, GenCompress, for genetic sequences, based on searching for approximate repeats. Our algorithm achieves the best compression ratios for benchmark DNA sequences. Significantly better compression results show that the approximate repeats are one of the main hidden regularities in DNA sequences. We then describe a theory of measuring the relatedness between two DNA sequences. Using our algorithm, we present strong experimental support for this theory, and demonstrate its application in comparing genomes and constructing evolutionary trees.

Journal Article↗

PubMed1997

Double coupling Edman chemistry for high-sensitivity automated protein sequencing.

Capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) is a promising new method for the analysis of protein sequencing products. It gives 10 zmol (1 zmol = 10(-21) mol) limits of detection (3 sigma) for fluorescein thiohydantoin (FTH) amino acids. We have developed a separation for the (FTH)-amino acid products generated from 18 of the 20 coded amino acids. The extremely low volume requirement associated with CE-LIF makes it incompatible with commercial sequencers. For this reason, we have also been developing a miniaturized sequencer that can be more easily coupled to our detection system. Both the CE-LIF system and the miniaturized sequencer are described.

Amino Acid Sequence↗

PubMed1996

Ability of serum prostate-specific antigen levels to predict normal bone scans in patients with newly diagnosed prostate cancer.

OBJECTIVES: To determine whether pretreatment serum prostate-specific antigen (PSA) levels in newly diagnosed prostate cancer patients can identify a group with a low probability of osseous metastasis and safely eliminate the need for a bone scan as a routine part of the staging evaluation. METHODS: We retrospectively reviewed 683 patients with prostate cancer between 1990 and 1993. Patients with prior therapy or serum PSA levels obtained longer than 3 months prior to bone scan were excluded. Bone scans were reviewed by two nuclear medicine physicians with a third deciding equivocal cases. RESULTS: Only 6% of 490 evaluable patients had a positive bone scan on initial evaluation. Scans were positive in 0 of 290 (0%) with PSA levels below 10 micrograms/L, 4 of 88 (4.5%) with PSA levels between 10 and 20 micrograms/L, and 24 of 112 (21%) with PSA levels above 20 micrograms/L. Although the risk of a positive bone scan increased with increasing PSA levels, PSA is a poor positive predictor of positive bone scans. The risk of a positive bone scan was 8% (5 of 64 patients) when PSA was between 20 and 50 micrograms/L, and increased to 40% (19 of 48 patients) for PSA levels greater than 50 micrograms/L. In contrast, serum PSA levels below 10 micrograms/L are strong negative predictors of positive bone scans, with no positive scans in 290 patients with PSA levels below 10 micrograms/L. Although the risk of a positive bone scan increased with increasing stage and grade, tumor stage and grade were poor negative predictors of positive bone scans. Up to 4% of patients with clinically confined or well-differentiated to moderately differentiated tumors had positive scans. Scans were positive in 12% of poorly differentiated tumors, but all these patients had PSA levels above 10 micrograms/L. CONCLUSIONS: Our data support the elimination of routine bone scintigraphy in patients with newly diagnosed prostate cancer and PSA levels below 10 micrograms/L. Bone scans are indicated when PSA levels are above 10 micrograms/L, or with T3 or poorly differentiated disease.

Adult↗

PubMed1995

Coupled reactions in hemoglobin. Heme-globin and dimer-dimer association.

Five different human hemoglobins were used to test the postulate that dissociation of hemoglobin (Hb) tetramers into alpha beta dimers and dissociation of heme from globin are linked reactions. Spectrophotometric measurements of the initial rate of heme transfer from Hb to serum albumin were made over a 3000-fold range of Hb concentration and yielded the heme-globin dissociation rate constant for tetramers and that for dimers. The tetramer-dimer dissociation constant (K4,2) could then be calculated from the rate constant at intermediate concentrations. The values obtained for the five hemoglobins, spanning a 250-fold range in K4,2, were in good agreement with those found by direct methods. The relation between this new linkage reaction of hemoglobin and the classical ones, such as the reciprocal relation between the binding of oxygen and protons, is discussed briefly.

Globins↗

PubMed1994

Quantitative transformation of hemoglobin into stable tetramers.

A method is described for the preparation of human or bovine hemoglobin with a covalent bridge, formed by bispyridoxal-tetraphosphate, between the beta chains. The yield is 95% of the total hemoglobin. The location of the two molecules of bispyridoxal-tetraphosphate in the tetramer has been established. The functional properties of the cross-linked hemoglobin, its stability, and particularly, the simplicity of the method for its preparation, make it a promising candidate for an acellular blood substitute.

Animals↗

PubMed1991

Hemoglobin tetramers stabilized by a single intramolecular cross-link.

A specific intramolecular cross-link was introduced into bovine and human hemoglobin by reaction of the deoxyhemoglobin with the dialdehyde, bispyridoxal tetraphosphate (bisPL)P4, followed by reduction with NaBH4. The yield of cross-linked hemoglobin is 80% in both cases, using 1 mol of (bisPL)P4 per mol of Hb. The crosslink is confined to the beta chains, where it connects the N-terminal residue (valine and methionine, respectively) to a lysine on the other beta chain across the central cavity. The stereochemical requirements for the reaction were probed by using a rigid analogous cross-linking reagent, as well as with a mutant Hb, which has a shorter distance between the residues to which the cross-link is attached. Introduction of the cross-link into human and bovine Hb results in a five-fold and four-fold reduction in the oxygen affinity and a decrease in the Bohr Effect by 1/3 and 1/2, respectively. Oxygenation remains cooperative, albeit with a decreased Hill coefficient. The cross-linked hemoglobins are oxidized more rapidly to the ferric form, but their resistance to heat denaturation is increased. The stability of the link between the beta chains and their hemes is 10 times greater in both cross-linked hemoglobins that in their native counterparts. The possible application of this chemical modification for the preparation of hemoglobin-based blood substitutes is discussed.

Animals↗

PubMed1990

The stability of the heme-globin linkage in some normal, mutant, and chemically modified hemoglobins.

The rates and equilibria of heme exchange between methemoglobin and serum albumin were measured using a simple new spectrophotometric method. It is based on the large difference between the spectrum of methemoglobin and that of methemealbumin at pH 8-9. The rate of heme exchange was found to be independent of the albumin concentration and inversely proportional to the hemoglobin (Hb) concentration. Taken together with the finding that the rate was 10 times greater for Hb Rothschild, which is completely dissociated into alpha beta dimers and 10 times smaller for two cross-linked hemoglobins, the subunits of which cannot dissociate, this showed that the rate of dissociation of heme from alpha beta dimers is very much greater than from tetramers. Conditions were found for the attainment of an equilibrium distribution of hemes between beta globin and albumin. The equilibrium distribution ratio, R = methemealbumin/albumin/methemoglobin/apohemoglobin, for hemoglobin A was 3.4 with human and 0.005 with bovine serum albumin. Both the rates of exchange and the R values of HbS and HbF were the same as that for HbA. The equilibrium distribution ratio for Hb Rothschild was 7 times greater than that for HbA whereas that of one but not the other of the cross-linked hemoglobins was 10 times smaller. The structural bases for these differences are analyzed.

Female↗

PubMed1988

Bis-pyridoxal polyphosphates: a new class of specific intramolecular crosslinking agents for hemoglobin.

A series of compounds related to bis-pyridoxal phosphate has been synthesized and used to crosslink deoxyhemoglobin. The yield of crosslinked hemoglobin increased dramatically from about 15% for the di- or triphosphate to about 70% for the tetraphosphate. The site of attachment of the intramolecular crossbridge was found to be from the N-terminal amino group of one beta chain to lysine 82 of the other. Since the distance between these residues is only 11A, the bis-pyridoxal tetraphosphates probably have a "stacked" conformation. The crosslinked hemoglobins bind oxygen cooperatively but with a greatly decreased affinity. The increased ability to unload oxygen together with the stabilization of the tetramer qualifies them as promising cell-free blood substitutes.

Cross-Linking Reagents↗

PubMed1988

p-Aminobenzoylpolyglutamates with hydrophobic end groups. A new class of inhibitors of hemoglobin S polymerization.

We have synthesized and tested a new series of compounds that inhibit the polymerization of deoxyhemoglobin S by noncovalent interaction. They consist of three structural elements: A p-aminobenzoyl residue to anchor the compound in the central cavity between the beta chains, a number of glutamates in gamma linkage to provide tight binding, and one or two hydrophobic amino acid residues which block the intermolecular hydrophobic interaction of valine beta 6. The most active compound was p-aminobenzoyl-(gamma-Glu)5-Phe-Phe. It increases the solubility of deoxy-HbS by a factor of 1.3 at a concentration of only 5-6 mM and is effective even in the presence of physiological concentrations of 2,3-diphosphoglycerate.

4-Aminobenzoic Acid↗

PubMed1986

Binding of diphosphoglycerate and ATP to oxyhemoglobin dimers.

The relative affinity of diphosphoglycerate and ATP for hemoglobin dimers and tetramers can be measured under conditions where the protein is in large molar excess over the polyphosphate. Binding of both compounds to dimers was about 25 times stronger than to tetramers in the case of the three low-spin hemoglobins, oxyhemoglobin, carboxyhemoglobin and cyanomethemoglobin. The mutation in hemoglobin Kansas leads to an increased dissociation into alpha beta dimers. The increase in diphosphoglycerate binding by this hemoglobin was in good agreement with that expected from the dimer-tetramer dissociation constant over a wide range of hemoglobin concentrations. In contrast to the liganded hemoglobins, both deoxyhemoglobin and aquomethemoglobin bind the two polyanions as tetramers.

Adenosine Triphosphate↗

PubMed1986

The interaction of folylpolyglutamates with deoxyhemoglobin. Identification of the binding site.

Previous studies have shown that pteroylheptaglutamate (PteGlu7) can form a 1:1 complex with deoxyhemoglobin. The solution and crystallographic studies reported in this paper delineate the nature of the PteGlu7 binding site. We find that the three structural elements of PteGlu7 (the pteridine moiety, the p-aminobenzoyl portion, and the glutamate groups) each contribute to the binding energy by interacting with residues in the central cavity between the beta subunits and with residues at the alpha 1 beta 1 interface. Identification of the 2,3-diphosphoglycerate (DPG) binding site as part of the PteGlu7 binding site was accomplished in two ways; first by the demonstration of reduced PteGlu7 binding to hemoglobin selectively modified by pyridoxylation at this site, and second by the finding that DPG and PteGlu7 bind to deoxyhemoglobin in a competitive manner. In addition, since analogs of PteGlu7 in which the pteridine moiety is modified display reduced binding, it can be concluded that the pteridine group also contributes significantly to the binding energy. The crystallographic studies are completely consistent with the results determined in solution. A difference electron density image at 4.3 A resolution shows that the pteridine and p-aminobenzoyl groups are nestled against an interior edge of the alpha 1 beta 1 interface with the pteridine ring interacting with Phe 36 alpha 1 and the p-aminobenzoyl group positioned against a portion of the H helix between residues Lys 132 beta 1 and Ala 135 beta 1. The difference density for the glutamate residues is less well resolved (for reasons described in the text), but it is clear that some of the carboxylate side chains must interact with residues at the DPG binding site.

Binding Sites↗

PubMed1985

The binding of folyl- and antifolylpolyglutamates to hemoglobin.

A binding method that detects only the strongest binding site for a ligand on a protein has been used to show that folates and folate analogs, conjugated with poly-gamma-glutamates, are bound to hemoglobin. When the concentration of hemoglobin is much larger than that of the polyglutamate, as is the case in the red cell, the fraction bound is a direct function of the hemoglobin concentration and is independent of the total polyglutamate concentration. Binding to deoxyhemoglobin tetramers is competitive with 2,3-diphosphoglycerate. In oxyhemoglobin the folyl and methotrexate polyglutamates are bound preferentially by free alpha beta dimers, but removal of the pteridine moiety leads to tetramer binding even in oxyhemoglobin. Changes in the length of the polyglutamate side chain and alterations of the pteridine structure such as reduction and/or methylation have a much larger effect on the constant for binding to deoxyhemoglobin tetramers than on that for oxyhemoglobin dimers. The implications of these results for the storage of pteroylpolyglutamates in the erythrocyte and their release from the red cell under the influence of the degree of oxygenation and variations in the 2,3-diphosphoglycerate level are discussed.

Folic Acid↗

PubMed1984

Changes in the Bohr effect due to pyridoxylation of the alpha-chain terminal amino groups of hemoglobin.

Deoxyhemoglobins substituted with pyridoxal 5'-phosphate or pyridoxal 5'-deoxymethylenephosphonate at the N-terminal amino groups of the alpha-chains were investigated by 31P-NMR spectroscopy. Titration curves of the 5'-side-chains show a substantial increase in acid strength in alpha-pyridoxylated deoxyhemoglobins when compared to the corresponding CO-liganded hemoglobins. These derivatives therefore contain a new oxygenation-linked acid group which opposes the normal Bohr effect. The loss in stabilization of the monoanion of the phosphate or phosphonate group derived from the three-dimensional structure can account for the lower pK of this ionization in deoxyhemoglobin as compared to CO-liganded hemoglobin. The reduction in the Bohr effect caused by modification of the alpha-chains with pyridoxal 5'-deoxymethyl-enephosphonate is quantitatively equal to the expected contribution of alpha-chain N-terminal amino groups.

Allosteric Regulation↗

PubMed1984

Enhanced oxygen unloading by an interdimerically crosslinked hemoglobin in an isolated perfused rabbit heart.

Coronary perfusion has shown that an intramolecularly crosslinked hemoglobin (Hb) with a very low affinity for O2 (Hb crosslinked covalently between the beta chains with 2-nor-2-formylpyridoxal 5'-phosphate, HbXL) has several advantages over ordinary Hb. As predicted from in vitro oxygenation curves, much more O2 was unloaded to the heart at three different heart rates, at two perfusion rates, and when the perfusate was equilibrated with 25% as well as 95% O2. In all cases, the improved O2 unloading occurred at higher tissue O2 pressures than with normal Hb. The greater O2 consumption with HbXL was accompanied by better mechanical performance because, after 90 min of perfusion, the HbXL-perfused hearts maintained two-thirds of their original contractility (dp/dt), while that of the Hb-perfused hearts had declined to one-fifth. A special advantage of HbXL is its ability to unload significant amounts of O2 even at low temperature (10 degrees C), in contrast to whole blood. This should make it useful for supporting aerobic metabolism during low-temperature cardioplegia in cardiac surgery and for organ preservation.

Animals↗