title: Reversibility and "pH-T phase diagrams" of Rapana venosa hemocyanin and its structural subunits.
abstract: We have studied the stability and reassociation behaviour of native molecules of Rapana venosa hemocyanin and its two subunits, termed RvH1 and RvH2. In the presence of different concentrations of Ca(2+) and Mg(2+) ions and pH values, the subunits differ not only in their reassociation behaviour, but also in their formation of helical tubules and multidecamers. RvH1 revealed a greater stability at higher pH values compared to RvH2. Overall, the stability of reassociated RvH and its structural subunits was found to be pH-dependent. The increasing stability of native Hc and its subunits, shown by pH-induced CD transitions (acid and alkaline denaturation), can be explained with the formation of quaternary structure. The absence of a Cotton effect at temperatures 20-40 degrees C in the pH-transition curves of RvH2 indicates that this subunit is stabilized by additional "factors", e.g.: non-ionic/hydrophobic stabilization and interactions of carbohydrate moieties. A similar behaviour was observed for the T-transition curves in a wide pH interval for RvH and its structural subunits. At higher temperatures, many of the secondary structural elements are preserved especially at neutral pH, even at extreme high temperatures above 90 degrees C the protein structures resemble a "globule state".
authors.affiliation: Interfacultary Institute of Biochemistry, University of Tübingen, Hoppe-Seyler-Strasse 4, D-72076 Tübingen, Germany.
authors.forename: Alexandar
authors.initials: A
authors.lastname: Dolashki
authors.forename: Lyudmila
authors.initials: L
authors.lastname: Velkova
authors.forename: Boris
authors.initials: B
authors.lastname: Atanasov
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Voelter
authors.forename: Stefan
authors.initials: S
authors.lastname: Stevanovic
authors.forename: Heinz
authors.initials: H
authors.lastname: Schwarz
authors.forename: Paolo
authors.initials: P
authors.lastname: Di Muro
authors.forename: Pavlina
authors.initials: P
authors.lastname: Dolashka-Angelova
mesh_terms: D000818:Animals; D002942:Circular Dichroism; D019281:Dimerization; D049851:Gastropoda / Q000737:chemistry* / Q000378:metabolism; D006433:Hemocyanins / Q000737:chemistry* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008962:Models, Theoretical; D011485:Protein Binding; D011489:Protein Denaturation; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D013696:Temperature
chemical_list: D021122:Protein Subunits; D006433:Hemocyanins