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In 1970, Perutz tried to put the allosteric mechanism of hemoglobin, proposed by Monod, Wyman and Changeux in 1965, on a stereochemical basis. He interpreted their two-state model in terms of an equilibrium between two alternative structures, a tense one (T) with low oxygen affinity, constrained by salt-bridges between the C-termini of the four subunits,(More)
The cooperative binding of oxygen by haemoglobin results from restraints on ligand binding in the T state. The unfavourable interactions made by the ligands at the haems destabilise the T state and favour the high affinity R state. The T <==> R equilibrium leads, in the presence of a ligand, to a rapid increase in the R state population and therefore(More)
Fix L, which contains a haemoglobin domain homologous to the PAS family and a histidine kinase domain, forms, with Fix J, a two-component signalling complex that regulates expression of nitrogenase genes in Rhizobium. Spin transitions of its haem iron trigger stereochemical changes in and around the haem that, together with steric effects, control the(More)
In 1972, Perutz proposed that the low affinity of T-state haemoglobin is caused by tension in the bond between the iron and the proximal histidine, restraining the Fe from moving into the porphyrin plane on binding oxygen. This proposal has often been disputed. If such tension does exist, it will be manifest in the liganded T-state. Here we describe the(More)
DnaD is a primosomal protein that remodels supercoiled plasmids. It binds to supercoiled forms and converts them to open forms without nicking. During this remodeling process, all the writhe is converted to twist and the plasmids are held around the periphery of large scaffolds made up of DnaD molecules. This DNA-remodeling function is the sum of a(More)
The paper presents an on-line dialectal resource, ALT-Web, which gives access to the linguistic data of the Atlante Lessicale Toscano, a specially designed linguistic atlas in which lexical data have both a diatopic and diastratic characterisation. The paper focuses on: the dialectal data representation model; the access modalities to the ALT dialectal(More)