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Biomedical subjects

F Siebert

Publications and source records attributed to F Siebert.

58 records · Page 4Linked to original sources
PubMed1978

Two distinct rhodopsin molecules within the disc membrane of vertebrate rod outer segments.

The kinetics of the metarhodopsin I-II reaction have been measured over a wide range of temperatures (1-37C ) and pH values (4.5-8) with suspensions containing fragments of bovine rod outer segments. It was found that for all conditions the occurrence of metarhodopsin II could be described by two independent first-order processes. The fast component: slow component amplitude ratio depends upon pH and temperature. The kinetics of the lumi-metarhodopsin I reaction show the same pH dependence for the fast component: slow component amplitude ratio as the one observed for the metarhodopsin II signals. All the results observed could be described with the assumption that rhodopsin itself exists in two conformational states before bleaching which are in a pH and temperature-dependent equilibrium. This hypothesis is confirmed by its ability to explain some apparently anomalous observations in the literature.

Animals↗
PubMedDate not supplied

Photoactivated state of rhodopsin and how it can form.

A variety of spectroscopic and biochemical studies of the photoreceptor rhodopsin have revealed conformation changes which occur upon its photoactivation. Assignment of these molecular alterations to specific regions in the receptor has been attempted by studying native opsin regenerated with synthetic retinal analogs or recombinant opsins regenerated with 11-cis retinal. We propose a model for the photoactivation mechanism which defines 'off' and 'on' states for individual molecular groups. These groups have been identified to undergo structural alterations during photoactivation. Analysis of mutant pigments in which specific groups are locked into their respective 'on' or 'off' states provides a framework to identify determinants of the active conformation as well as the minimal number of intramolecular transitions to switch to this conformation. The simple model proposed for the active-state of rhodopsin can be compared to structural models of its ground-state to localize chromophore-protein interactions that may be important in the photoactivation mechanism.

Amino Acid Sequence↗
PubMedDate not supplied

The effect of serum and allogeneic antiglobulin preparations on the mitogenic reactivity of peripheral blood lymphocytes from patients with rheumatoid arthritis.

In vitro transofrmation of peripheral blood lymphocytes (PBL) by phytohaemagglutinin (PHA) and concanavalin A (Con A) was found to be decreased in 17 RA patients. The addition of 50 microliter RA serum or serum from normal controls exhibited an inhibitory effect on the mitogenic reactivity to Con A but not to PHA of both normal and RA patient's PBL. Allogeneic antiglobulin preparations (a-Ig) stimulated the spontaneous in vitro DNA synthesis of PBL from normal control and, to a smaller degree, also from RA patients. The simultaneous addition of a-Ig's and mitogens to PBL of normal controls and RA patients did not exhibit a significant effect on the mitogenic reactivity.

Antibodies, Anti-Idiotypic↗