title: 87Rb+ spin relaxation in enzymically purified and in untreated iota-carrageenan.
abstract: The temperature dependences of the transverse (R2) and longitudinal (R1) n.m.r. relaxation rates of 87Rb+ in aqueous 5% iota-carrageenan have been compared with similar data for a sample purified by treatment with kappa-carrageenase. In each sample, the relaxation rates were sensitive to the conformation (helix or random coil). In the intact sample, the small (less than or equal to 5%) fraction of kappa-carrageenan (which, in its helical state, specifically binds rubidium ions) was solely responsible for the pronounced line-broadening that has been observed hitherto for 87Rb in iota-carrageenan gels. In the purified sample, the effects on the relaxation of 87Rb induced by iota-carrageenan are similar to those found in comparable systems in the absence of site-binding of the ions. Thus, there was a modest enhancement of the relaxation with R1 approximately R2 for the flexible coil conformation and a comparably larger effect, with significant contributions from dynamic processes on the time-scale of the inverse resonance frequency or longer, for the thicker, more highly charged and rigid helix conformation of iota-carrageenan.
authors.affiliation: Physical Chemistry 1, University of Lund, Chemical Center, Sweden.
authors.forename: L
authors.initials: L
authors.lastname: Piculell
authors.forename: C
authors.initials: C
authors.lastname: Rochas
mesh_terms: D001426:Bacterial Proteins; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002247:Carbon Isotopes; D002351:Carrageenan / Q000737:chemistry* / Q000302:isolation & purification; D006026:Glycoside Hydrolases; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008956:Models, Chemical; D008969:Molecular Sequence Data; D009904:Optical Rotation; D012414:Rubidium Radioisotopes
chemical_list: D001426:Bacterial Proteins; D002247:Carbon Isotopes; D012414:Rubidium Radioisotopes; D002351:Carrageenan; D006026:Glycoside Hydrolases; C019846:kappa-carrageenase protein, Alteromonadaceae