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Biomedical subjects

D M Chen

Publications and source records attributed to D M Chen.

14 recordsLinked to original sources
PubMed1992

Visual receptor cycle in normal and period mutant Drosophila: microspectrophotometry, electrophysiology, and ultrastructural morphometry.

Visual pigment, sensitivity, and rhabdomere size were measured throughout a 12-h light/12-h dark cycle in Drosophila. Visual pigment and sensitivity were measured during subsequent constant darkness [dark/dark (D/D)]. MSP (microspectrophotometry) and the ERG (electroretinogram) revealed a cycling of visual pigment and sensitivity, respectively. A visual pigment decrease of 40% was noted at 4 h after light onset that recovered 2-4 h later in white-eyed (otherwise wild-type, w per+) flies. The ERG sensitivity [in w per+ flies in light/dark (L/D)] decreased by 75% at 4 h after light onset, more than expected if mediated by visual pigment (MSP) changes alone. ERG sensitivity begins decreasing 8 h before light onset while decreases in visual pigment begin 2 h after light onset. These cycles continue in constant darkness (D/D), suggesting a circadian rhythm. White-eyed period (per) mutants show similar cycles of visual pigment level and sensitivity in L/D; per's alterations, if any on the D/D cycles were subtle. The cross-sectional areas of rhabdomeres in w per+ were measured using electron micrographic (EM) morphometry. Area changed little through the L/D cycle.

Animals↗
PubMed1992

Electrophysiological sensitivity of carotenoid deficient and replaced Drosophila.

R1-6 dominated electroretinographic (ERG) spectral sensitivities were determined as a function of days posteclosion from carotenoid deprived and replaced white-eyed Drosophila. The sensitivity of flies deprived from egg to adult waxed (about 1.5 log units by day 3), and then waned gradually from 3-11 days (over 2 log units by day 11). Carotenoid replacement (feeding nothing but carrot juice) effected recovery to near the replete controls' level in about 1 day throughout (tested at 0, 4, and 11 days). The normal yellow cornmeal-agar-molasses-brewers yeast fly food (in our laboratory, supplemented with beta-carotene) renders a slower recovery (requiring 7-9 days) since it is a medium designed largely for larval growth. Placing replete adults on deprivational medium did not create a deprivational syndrome in over 11 days. At 3-7 days, deprived flies reared and maintained in constant darkness had substantially enhanced sensitivity, beyond the 1.5 log unit increment already described for cyclic light rearing conditions. All spectral analyses are consistent with the ultraviolet (UV) sensitization of the blue (480 nm) rhodopsin by a replacement-dependent retinoid including two unexpected findings: (1) sensitivity recovery with carrot juice was so fast that the UV peak was already high at 6 h; and (2) the waxing of the deprived fly's sensitivity in dark rearing was so great that the UV peak was present at 4-7 days.

Animals↗
PubMed1978

An analysis of the Co2+-induced nuclear magnetic resonance perturbations of hen egg white lysozyme.

A general methodology is presented for analyzing dipolar shifts induced by paramagnetic ions in the nuclear magnetic resonance (NMR) spectra of ligand molecules. The method is applied to the shift perturbations induced by Co2+ in the spectrum of hen egg white lysozyme. A hypothesis testing scheme is employed to evaluate statistically the relative precision with which the axially symmetric and non-axially symmetric forms of the dipolar shift equation fit the observed data. The assumption of axial symmetry for the magnetic susceptibility tensor of Co2+ is rejected at the confidence level of 99%. Since the results presented here are similar to those reached in our analysis of lanthanide-induced shifts, we suggest that the assumption of axial symmetry may, in general, not hold. Similar conclusions have been reached by other investigators in studies of paramagnetic metal binding to model systems. We have included the three Co2+ coordinates in an eight-parameter fit of the Co2+ shift data. The Co2+ position obtained from this fit is in statistical agreement with the position inferred from x-ray data. Thus, the analysis of shift data may furnish a means for determining the site of metal complexation in macromolecules whose structure has been determined by x-ray crystallography.

Animals↗
PubMed1977

Nuclear magnetic resonance studies of the denaturation of ubiquitin.

The effects of pH, temperature and guanidine hydrochloride concentration on the structure of ubiquitin, a polypeptide which can activate adenylate cyclase and can mimic thymopoietin induced differentiation of prothymocytes, were monitored using nuclear magnetic resonance spectroscopy. This relatively small polypeptide (molecular weight of 8541) exhibits a remarkable stability towards pH and temperature changes. At 7 M guanidine hydrochloride concentration, the structure of ubiquitin is essentially a random coil.

Guanidines↗
PubMed1977

Proton nuclear magnetic resonances study of bleomycin in aqueous solution. Assignment of resonances.

The 1H NMR spectrum of the glycopeptide antineoplastic antibiotic bleomycin has been examined in D2O solution (Fourier transform nuclear magnetic resonance, 270 MHZ) and in H2O solution (correlation nuclear magnetic resonance, 250 MHZ). Resonances have been assigned to specific hydrogens of the two most abundant congeners, bleomycin-A2 (BLM-A2) and bleomycin-B2 (BLM-B2), on the basis of (1) homonuclear spin decoupling, (2) comparison of the spectra of BLM-A2, BLM-B2, fragments of these antibiotics, and the related antibiotic phleomycin, and (3) the pH dependence of chemical shifts. Resonance assignments are presented for all the CH protons of BLM-A2 and BLM-B2 except for the saccharide groups, for which only the anomeric proton assignments are given. All of the NH protons have been identified with specific resonances except for the two primary amide groups, which yield four well-resolved peaks, whose specific assignment was not attempted. This study serves as a basis for future investigations of the conformation of bleomycin and its interaction with metals and nucleic acids.

Bleomycin↗
PubMed1977

Effect of serum and serum components on the mitogen-induced proliferation of murine lymphocytes.

By increasing the concentration of human serum, the dose-response profile of the Concanavalin A-induced proliferation of murine spleen lymphocytes becomes broader and the optimal cell proliferation takes place at higher concentrations of mitogen. It is shown that this behavior is due to the globulin fraction of serum which greatly decreases the binding of Concanavalin A to lymphocytes. Cohn fractions III and IV have a similar effect. On the other hand, cell proliferation takes place also in the absence of Pooled Human Serum at appropriate concentrations of Concanavalin A and within a very narrow range of cell concentrations. In the presence of the albumin fraction of serum, proliferation takes place over a wider range of mitogen and cell concentrations. As a result of these phenomena, the mitogenic effect of Concanavalin A varies greatly in function of the concentration of serum. Analogous results were obtained with fetal calf serum.

Animals↗
PubMed1977

Some immunological effects of penicillamine.

Immunological effects of D- and D,L-penicillamine (PA) were studied in efforts to develop assays for synthetic D or D,L analogs and to contribute to the understanding of the mechanism(s) of action of D-PA in rheumatoid arthritis. At the highest doses tolerated by mice, D,L-PA did not significantly inhibit the development of haemagglutinating antibodies in vivo. In studies in vitro with T lymphocytes, D-PA at 1 mM concentration inhibited both concanavalin A- and phytohaemagglutinin-induced transformation as assayed by [3H]thymidine incorporation, but D-PA concentrations of 5 mM were required to inhibit concanavalin A-induced amino acid uptake. No effect of D-PA was observed either on the induction of cytotoxic T cells or on the attack of specifically sensitized T cells on target cells. It is of interest that D-PA at 1 mM concentration did inhibit lipopolysaccharide-induced transformation, which predominately stimulates B lymphocytes. The effects of PA on the induced transformation of T and B cells deserve further attention for studies with analogs of PA.

Animals↗