Biomedical subjects

D Mead

Publications and source records attributed to D Mead.

13 recordsLinked to original sources

PubMed1995

Expression of drug resistance-associated mdr-1, GST pi, and topoisomerase II genes during cell cycle traverse.

The expression of drug resistance-associated mdr-1, GST pi, and topoisomerase II genes was analyzed in cell cycle phase enriched populations of doxorubicin-resistant murine leukemic P388/R-84 cells. Flow cytometric analysis of bromodeoxyuridine (BrdU) incorporation and staining with anti-BrdU antibodies was used to confirm the purity of cell cycle phase enriched populations obtained by centrifugal elutriation. Doxorubicin (DOX) and daunorubicin (DNR) accumulation was significantly lower in S-phase cells, and coincubation with verapamil (VPL) or chlorpromazine (CPZ) enhanced DOX and DNR accumulation more in S-phase than in G1- and G2/M-phase cells. While the cellular content of mdr-1 and topoisomerase II mRNAs changed, GST pi mRNA content remained constant during the cell cycle. S-phase cells had about 3-fold higher mdr-1 mRNA content than G1- and G2/M-phase cells. In G1 cells, P-glycoprotein expression, as determined by C219 monoclonal antibody, was 12% less than that of S and G2/M cells. Topoisomerase II mRNA content increased with the progression of cell cycle and peaked in G2/M cells. These observations suggest that cell cycle stage related changes in expression of drug resistance markers may have a major bearing on chemosensitivity of drug-resistant cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1992

The integration of a database and a statistical program in the analysis of a large scale survey in nursing.

Large scale surveys have conventionally been analysed using a statistical package. This saves considerable time and permits many more analyses to be undertaken than with more traditional methods. It does, however, have certain drawbacks. First, it does not help with the problem of data management. SPSS and Epfino, for example, have some facilities for data entry restrictions and cross-checking. They are excellent for the static purpose for which they are designed, but rather crude in comparison with those provided by a dedicated database tool. Second, it requires considerable experience to achieve maximum benefit. Third, it does not help at all in the major undertaking of data exploration. The authors have analysed a large scale survey using a statistical package and a database in collaboration. Their experience is reported here.

Databases, Bibliographic↗

PubMed1991

NMR studies of fluorinated visual pigment analogs.

The 19F-nmr chemical shift data of isomeric pigments (11-cis and 9-cis) of four vinyl fluororhodopsins and two trifluororhodopsins have been recorded. When compared with model protonated Schiff bases, a set of F-nmr opsin shift parameter (FOS) was obtained. The data revealed regiospecific protein perturbations on the F-resonances. They can be interpreted in terms of specific protein interactions such as the postulated second point charge and other polar interactions as well as the common hydrophobic protein perturbation.

Fluorine↗

PubMed1990

14-Fluorobacteriorhodopsin and other fluorinated and 14-substituted analogues. An extra, unusually red-shifted pigment formed during dark adaptation.

Five vinyl-substituted fluororetinal analogues (8-F, 10-F, 12-F, 14-F, and 13,14-F2) were found to give bacteriorhodopsin analogues with properties similar to those of the parent system. Of these, only 14-fluororetinal was found to give an extra red-shifted BR analogue (lambda max less than or equal to 680 nm) in equilibrium with the normal 587-nm pigment. The 680-nm pigment was enriched upon irradiation. It rearranged to the 587-nm pigment at room temperature (delta E [symbol: see text] = 20.8 kcal/mol). Chromophore extraction experiments revealed the all-trans geometry for the 680-nm pigment. 14-Chlororetinal gave a similarly red-shifted pigment while 14-methylretinal did not. A scheme for dark adaptation of the 14-halogenated bacteriorhodopsins has been proposed in which the new red-shifted pigment was assigned the all-trans, 15-syn geometry.

Bacteriorhodopsins↗

PubMed1990

Comparative study on the chromophore binding sites of rod and red-sensitive cone visual pigments by use of synthetic retinal isomers and analogues.

A comparative study on the chromophore (retinal) binding sites of the opsin (R-photopsin) from chicken red-sensitive cone visual pigment (iodopsin) and that scotopsin) from bovine rod pigment (rhodopsin) was made by the aid of geometric isomers of retinal (all-trans, 13-cis, 11-cis, 9-cis, and 7-cis) and retinal analogues including fluorinated (14-F, 12-F, 10-F, and 8-F) and methylated (12-methyl) 11-cis-retinals. The stereoselectivity of R-photopsin for the retinal isomers and analogues was almost identical with that of scotopsin, indicating that the shapes of the chromophore binding sites of both opsins are similar, although the former appears to be somewhat more restricted than the latter. The rates of pigment formation from R-photopsin were considerably greater than those from scotopsin. In addition, all the iodopsin isomers and analogues were more susceptible to hydroxylamine than were the rhodopsin ones. These observations suggest that the retinal binding site of iodopsin is located near the protein surface. On the basis of the spectral properties of fluorinated analogues, a polar group in the chromophore binding site of iodopsin as well as rhodopsin was estimated to be located near the hydrogen atom at the C10 position of the retinylidene chromophore. A large difference in wavelength between the absorption maxima of iodopsin and rhodopsin was significantly reduced in the 9-cis and 7-cis pigments. On the assumption that the retinylidene chromophore is anchored rigidly at the alpha-carbon of the lysine residue and loosely at the cyclohexenyl ring, each of the two isomers would have the Schiff-base nitrogen at a position altered from that of the 11-cis pigments.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Positive charges at the NH2 terminus convert the membrane-anchor signal peptide of cytochrome P-450 to a secretory signal peptide.

The NH2-terminal sequences of cytochromes P-450 resemble signal peptides, but these sequences are not cleaved during the insertion of these integral membrane proteins into the microsomes. To examine whether these putative signal peptides are functionally equivalent to signal peptides of secretory proteins, cDNA coding for a fusion protein was produced, in which the signal peptide for preproparathyroid hormone was replaced with the putative signal peptide of cytochrome P450IIC2. The translational product of RNA synthesized in vitro from the cDNA was neither processed nor translocated by chicken oviduct microsomal membranes in a reticulocyte cell-free system but was resistant to extraction from the membranes by alkaline solutions. In addition, the translation of the hybrid RNA was arrested by signal recognition particle. Unlike most signal peptides, the cytochrome P450IIC2 NH2-terminal sequence does not contain basic amino acids preceding the hydrophobic core. Introduction by oligonucleotide-directed mutagenesis of lysine and arginine at the NH2 terminus resulted in a fusion protein that was partially processed by the microsomal membranes, with translocation across the membrane of both the processed and unprocessed proteins. The positive charges convert the cytochrome P450IIC2 NH2 terminus from a combination membrane insertion-halt transfer signal to a more classical secretory membrane-insertion signal, possibly by altering the orientation of the signal peptide in the membrane.

Amino Acid Sequence↗

PubMed1983