Showing papers on "Signal transduction published in 1979"

Relation of Chemotactic Response to the Amount of Receptor: Evidence for Different Efficiencies of Signal Transduction

Abstract: We determined the content of galactose-glucose-, maltose-, and ribose-binding proteins in cells of Escherichia coli K-12 grown in a variety of media and also measured the respective transport and chemotactic activities that depend on those binding proteins. Correlation of the level of induction of a particular binding protein with the extent of tactic activity mediated by that protein indicates that the magnitude of the tactic response to a particular stimulating compound is a direct function of the number of receptors per cell. In contrast, comparison of the magnitudes of response to substances recognized by independent receptors indicates that some stimulus-receptor complexes are more effective in eliciting tactic responses than are others. Thus, the magnitude of response to any particular stimulating compound is a function both of the number of receptors per cell and of the effectiveness of the stimulus-receptor complex. Considerations of available information about the tactic response to maltose suggest that the effectiveness of a stimulus-receptor complex is related to the transducer with which the receptor interacts. The tar product appears to be a relatively effective transducer of the signals it accepts from receptors for aspartate, α-methylaspartate, and maltose, whereas the trg product appears to be a relatively ineffective transducer of signals it accepts from receptors for galactose and ribose.

Distinction Between the Rate Theory and the Occupation Theory of Signal Transduction By Receptor Activation

Abstract: Two ways to describe the response after an interaction between a ligand and a receptor are the rate theory and the occupation theory The response of rate receptors is proportional to the rate of association while the response of occupation receptors is proportional to the fraction of receptors occupied Ligands are bound to receptors by dipole bonds and ionic and hydrophobic interactions Ligand derivatives in which one or more atomic interactions with the receptor cannot take place will dissociate faster than the natural ligand A faster dissociation from a rate receptor allows more associations between the derivative and the receptor resulting in a higher maximal response than with the natural ligand The maximal response of an occupation receptor to the natural ligand and to a ligand derivative are the same Analysis of dose-response curves allows discrimination between these two receptors even if the response can only be recorded a long period after the activation of the receptor

Initiation of protein synthesis in prokaryotes.

Abstract: The study of the regulation of initiation of protein synthesis has recently gained momentum because of the established relationship between translation initiation, cell growth and tumorigenesis Therefore much effort is devoted to the role of protein kinases which are activated in signal transduction cascades and which are responsible for the phosphorylation of a number of initiation factors These specific factors are mainly involved in the binding of messenger RNA to the 40S ribosome, a process that makes the unwinding of the 5′ untranslated region necessary It appears that the phosphorylation of these factors increases their ability for cap recognition and helicase activity The enhanced phosphorylation of the messenger binding factors results not only in an overall stimulation of translation, but especially weak messengers are positively discriminated The above mechanisms mainly deal with qualitative control of translation, ie, messenger selection, but phosphorylation also plays a role in quantitative regulation of protein synthesis The generation of active eIF-2, the initiation factor that binds the Met-tRNA i and GTP, is dependent on a factor involved in the GDP-GTP exchange Phosphorylation of eIF-2 results in sequestration of the exchange factor and a slowing down of the rate of initiation

The Fat Cell Adenylate Cyclase System: Characterization and Manipulation of Its Biomodal Regulation by GTP

Abstract: The second of two articles in which Rodbell indicated that in addition to transducing hormone signals across the membrane, the G-protein could also inhibit signaling at the discriminator point. He provided evidence that G-proteins at the cellular receptors were sophisticated enough to both inhibit and activate signal transduction.