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Biomedical subjects

K K Millis

Publications and source records attributed to K K Millis.

10 recordsLinked to original sources
PubMed1998

Resource allocation during the rereading of scientific texts.

Two experiments examined how cognitive resources are allocated to comprehension processes across two readings of the same scientific texts. In Experiment 1, readers read and later reread texts describing scientific topics. The results indicated that across readings, readers decreased resources allocated to proposition assembly, increased resources allocated to text-level integration, and expended a similar amount of resources to lexical access. Subjects who reread the texts after a week delay showed a similar pattern, except that they did not show the increase for text-level integration. Experiment 2 revealed a similar pattern of results with a moving window procedure, except that there was a significant decrease in resources allocated to lexical access across exposures. This experiment also indicated that the rereading speedup was greatest at sentence boundaries, suggesting that the prior exposure enabled readers to immediately process each word. Overall, the results are consistent with the claim that readers allocate proportionally more available resources to text-level integration during rereading because proposition assembly, which enables text-level integration, can be completed with fewer resources.

Adult↗
PubMed1997

Kinetics of the conjugation of aniline mustards with glutathione and thiosulfate.

The rates of the non-enzymatic conjugation of the substituted aniline mustards, melphalan, chlorambucil and p-(N,N-bis(2-chloroethyl))toluidine with glutathione and thiosulfate were determined using nuclear magnetic resonance spectroscopy. Using this method, the disappearance of drug and the formation of both the mono-thioether and bis-thioether conjugates can be monitored directly. For glutathione conjugation, the rate constants for the formation of the first and second aziridinium intermediates were similar. With thiosulfate conjugation, the rate constant for the formation of the first aziridinium intermediate is greater than the rate constant for the formation of the second aziridinium. This demonstrates that the type of nucleophile has a significant influence on the overall alkylating activity of these bifunctional mustards. The bisthioether adduct formed from the reaction between p-(N,N-bis([2-13C]-2-chloroethyl))toluidine and glutathione and thiosulfate can be identified and scrambling of the 13C label in the product provides strong evidence that the alkylation must occur through an aziridinium intermediate.

Aniline Mustard↗
PubMed1997

Gradient, high-resolution, magic-angle spinning nuclear magnetic resonance spectroscopy of human adipocyte tissue.

The recently developed technique of gradient, high-resolution magic-angle spinning NMR (g-hr-MAS-NMR) spectroscopy was applied to the study of ex vivo human lipoma and liposarcoma tissue. Compared with conventional 1H-NMR, the g-hr-MAS method yielded a large improvement in spectral resolution and permitted the detection of metabolite resonance's in a well-differentiated liposarcoma that was not observed in spectra of similar samples obtained using nonspinning NMR methods. These findings suggest that g-hr-MAS-NMR spectroscopy provides a key improvement in spectral quality for ex vivo lipoma and liposarcoma tissue thereby permitting a more precise determination of tissue metabolite composition than conventional nonspinning NMR methods.

Adipocytes↗
PubMed1997

Formation, intracellular distribution and efflux of glutathione-bimane conjugates in drug-sensitive and -resistant MCF-7 cells.

The rate of reaction of monochlorobimane with glutathione (GSH) was measured in native human mammary MCF-7 adenocarcinoma cells (MCF-7wt) and sublines displaying resistance to 4-hydroperoxycyclophosphamide (MCF-7hc) and adriamycin (MCF-7adr) prior to examination by epifluorescence and confocal microscopy. After a 60-min incubation period at 37 degrees C, essentially all GSH was conjugated in the MCF-7wt and MCF-7adr cell lines whereas only 80% of the GSH was conjugated in the MCF-7hc line. All three lines displayed significant export of the conjugate from the cell during this period, with the MCF-7adr line displaying the most rapid efflux with 85% of the conjugate exported within 60 min. Epifluorescence microscopy detected an approximately 20% increase in integrated fluorescence intensity in the nuclear region in all three lines. Confocal microscopy however, indicated that most of the cells examined showed a homogeneous fluorescence distribution. The cells grown in monolayers were found to be thicker in the nuclear region suggesting that the observed increase in fluorescence intensity in the nuclear region in the images from epifluorescence microscopy was probably derived from fluorescence from an out-of-focus plane. Cells depleted of GSH with buthionine sulfoximine followed by treatment with mBCl showed significant fluorescence intensity resulting from nonspecific binding of this probe. These studies illustrate the need for measuring the rate of GSH conjugate export and for determining probe specificity, and emphasizes the need for using confocal techniques for the quantitative evaluation of the distribution of intracellular fluorescence.

Adenocarcinoma↗
PubMed1997

Discourse comprehension.

The field of discourse processing has dissected many of the levels of representation that are constructed when individuals read or listen to connected discourse. These levels include the surface code, the propositional textbase, the referential situation model, the communication context, and the discourse genre. Discourse psychologists have developed models that specify how these levels are mentally represented and how they are dynamically built during comprehension. This chapter focuses on the meaning representations that are constructed when adults read written text, such as literary stories, technical expository text, and experimenter-generated "textoids." Recent psychological models have attempted to account for the identification of referents of referring expressions (e.g. which person in the text does she refer to), the connection of explicit text segments, the establishment of local and global coherence, and the encoding of knowledge-based inferences.

Journal Article↗
PubMed1995

Comparison of the protonation of isophosphoramide mustard and phosphoramide mustard.

The alkylating agent isophosphoramide mustard (IPM) spontaneously forms a relatively stable aziridine derivative which can be directly observed using NMR spectroscopy. The protonations of IMP and its aziridine were probed using 1H, 31P, 15N, and 17O NMR spectroscopy. The positions of the 31P, 15N, and 17O resonances of IPM between pH 2 and 10 each exhibit a single monobasic titration curve with the same pKa of 4.31 +/- 0.02. On the basis of a comparison with other compounds and our earlier work with phosphoramide mustard, the NMR results for IPM indicate that protonation occurs at nitrogen and not oxygen. Over this same pH range, each of the 1H, 31P, and 15N resonances of IPM-aziridine also show a single monobasic titration with a pKa of 5.30 +/- 0.09. The magnitude of the change in chemical shifts suggests that the protonation of the IPM-aziridine occurs at the ring nitrogen. Theoretical gas-phase calculations of PM, IPM, and IPM-aziridine suggest O-protonation to be more likely; however, aqueous phase calculations predict the N-protonated forms to be most stable. Furthermore, for PM and IPM-aziridine, which contain nonequivalent nitrogens, the theoretical calculations and experimental data both agree as to which nitrogen undergoes protonation. These results suggest that the IMP-aziridine remains unprotonated under physiological conditions and may, in part, explain the lower alkylating activity of IPM as compared to PM.

Antineoplastic Agents↗
PubMed1995

Nuclear magnetic resonance study of the thioltransferase-catalyzed glutathione/glutathione disulfide interchange reaction.

The kinetics of the thioltransferase-catalyzed symmetrical glutathione/glutathione disulfide (GSH/GSSG) interchange reaction have been studied by 1H-nuclear magnetic resonance spectroscopy. Kinetic parameters were determined by analysis of exchange-broadened multiplet patterns and by the inversion-magnetization transfer method using concentrations of GSH, GSSG and pig liver thioltransferase similar to intracellular concentrations. The rate constant for the reaction of GSSG with thioltransferase to form a thioltransferase-glutathione mixed disulfide and GSH was estimated to be > or = 7.1(+/- 0.4).10(5) M-1 s-1. This reaction is proposed to be the first step in the mechanism by which the activity of some proteins is modulated by the thioltransferase-catalyzed formation of protein-glutathione mixed disulfides. The rate constant for the reaction of GSSG with thioltransferase is 4-5 orders of magnitude larger than rate constants for the analogous reaction of the thiolate groups of a variety of small molecules with GSSG. The symmetrical gamma-L-glutamyl-L-cysteine/gamma-L-glutamyl-L-cysteine disulfide (GCSH/GCSSCG), L-cysteinyl-glycine/L-cysteinyl-glycine disulfide (CGSH/CGSSGC) and cysteine/cystine (CSH/CSSC) thiol/disulfide interchange reactions were also studied as models for the GSH/GSSG interchange reaction. The GCSH/GCSSCG interchange reaction was found to be catalyzed by thioltransferase, and the rate constant for the reaction of GCSSCG with thioltransferase was estimated to be > or = 5.7(+/- 1.7).10(4) M-1 s-1. In contrast, the CGSH/CGSSGC and CSH/CSSC interchange reactions were found to be slow on the NMR time-scale for the conditions used in this research, both in the absence and presence of thioltransferase. The results suggest that the gamma-L-glutamyl-L-cysteinyl moiety of GSSG and of GSH-containing mixed disulfides is essential for their recognition by thioltransferase.

Animals↗
PubMed1995

Noninvasive detection of elevated glutathione levels in MCF-7 cells resistant to 4-hydroperoxycyclophosphamide.

Native human mammary MCF-7 adenocarcinoma cells and a subline displaying resistance to 4-hydroperoxycyclophosphamide, the chemically activated form of cyclophosphamide, were grown as multicellular spheroids or on a collagen sponge matrix and perfused for study by 31P and 13C nuclear magnetic resonance spectroscopy. The natural abundance 13C spectrum of the perfused cells exhibits well-resolved resonances due to the intracellular glutathione (GSH). The resistant cell line shows a higher intensity of the GSH 13C resonances, consistent with the increased GSH concentration determined from biochemical assays of extracts. Treatment of the resistant cell line with buthionine sulfoximine selectively diminishes the intensity of the GSH resonances in the 13C nuclear magnetic resonance spectrum.

Breast Neoplasms↗
PubMed1990

1H-nuclear magnetic resonance study of the oxidation/reduction chemistry of penicillamine in intact human erythrocytes.

The oxidation/reduction chemistry of penicillamine in human erythrocytes was characterized directly in intact erythrocytes by 1H-NMR spectroscopy. Spectra were measured by the Carr-Purcell-Meiboom-Gill pulse sequence to selectively eliminate interfering resonances from hemoglobin and membrane protons and from the intracellular water. Glucose-free penicillamine-containing erythrocytes were subjected to oxidative stress by titration with t-butyl hydroperoxide. The t-butyl hydroperoxide rapidly crosses the erythrocyte membrane and reacts with glutathione (GSH) and penicillamine (PSH), with the PSH being oxidized to penicillamine-glutathione mixed disulfide (PSSG) as indicated by the appearance of characteristic resonances in the high resolution 1H-NMR spectrum. Extracellular PSH is oxidized to penicillamine disulfide (PSSP) when t-butyl hydroperoxide is added to the cells and thereafter in amounts dependent on the oxygenation state of the sample. Following addition of glucose, both the oxidized glutathione and the PSSG are rapidly reduced at comparable rates. The results of additional experiments using erythrocyte lysate and of kinetic experiments on solutions containing PSSG and/or GSH, NADPH and glutathione reductase suggest that the predominant mechanism for reduction of PSSG is by a thiol-disulfide exchange reaction with GSH to form PSH and GSSG, which in turn undergoes enzyme-catalyzed reduction by NADPH.

Blood Glucose↗