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D Lancet

Publications and source records attributed to D Lancet.

101 records · Page 6Linked to original sources
PubMed1976

Kinetic evidence for hapten-induced conformational transition in immunoglobin MOPC 460.

The kinetics of hapten binding to the homogeneous immunoglobulin A secreted by the murine plasmacytoma MOPC 460 was investigated by the chemical relaxation method. Two distinct relaxation times were observed in the binding equilibrium with three different haptens. A detailed concentration dependence analysis of relaxation times and amplitudes was performed with the hapten epsilon-N(2,4-dinitrophenyl)-lysine (Dnp-Lys). The results support a mechanism in which two interconvertible conformational states of the protein bind the hapten with different association constants. Hapten binding shifts the equilibrium towards the better binding state. These observations form kinetic evidence for a conformational transition induced in the immunoglobulin by ligand binding to its antigen binding site, and are in line with the allosteric hypothesis for the initiation of physiological functions by antigen-antibody association.

Allosteric Regulation↗
PubMedDate not supplied

The lipid world.

The continuity of abiotically formed bilayer membranes with similar structures in contemporary cellular life, and the requirement for microenvironments in which large and small molecules could be compartmentalized, support the idea that amphiphilic boundary structures contributed to the emergence of life. As an extension of this notion, we propose here a 'Lipid World' scenario as an early evolutionary step in the emergence of cellular life on Earth. This concept combines the potential chemical activities of lipids and other amphiphiles, with their capacity to undergo spontaneous self-organization into supramolecular structures such as micelles and bilayers. In particular, the documented chemical rate enhancements within lipid assemblies suggest that energy-dependent synthetic reactions could lead to the growth and increased abundance of certain amphiphilic assemblies. We further propose that selective processes might act on such assemblies, as suggested by our computer simulations of mutual catalysis among amphiphiles. As demonstrated also by other researchers, such mutual catalysis within random molecular assemblies could have led to a primordial homeostatic system displaying rudimentary life-like properties. Taken together, these concepts provide a theoretical framework, and suggest experimental tests for a Lipid World model for the origin of life.

Catalysis↗
PubMedDate not supplied

Odorant-sensitive adenylate cyclase may mediate olfactory reception.

The mechanism of the sense of smell has long been a subject for theory and speculation. More recently, the notion of odorant recognition by stereospecific protein receptors has gained wide acceptance, but the receptor molecules remained elusive. The recognition molecules are believed to be quite diverse, which would partly explain the unusual difficulties encountered in their isolation by conventional ligand-binding techniques. An alternative approach would be to probe the receptors through transductory components that may be common to all receptor types. Here we report the identification of one such transductory molecular component. This is an odorant-sensitive adenylate cyclase, present in very large concentrations in isolated dendritic membranes of olfactory sensory neurones. Odorant activation of the enzyme is ligand and tissue specific, and occurs only in the presence of GTP, suggesting the involvement of receptor(s) coupled to a guanine nucleotide binding protein (G-protein). The olfactory G-protein is independently identified by labelling with bacterial toxins, and found to be similar to stimulatory G-proteins in other systems. Our results suggest a role for cyclic nucleotides in olfactory transduction, and point to a molecular analogy between olfaction and visual, hormone and neurotransmitter reception. Most importantly, the present findings reveal new ways to identify and isolate olfactory receptor proteins.

Adenylyl Cyclases↗