title: Proton exchange as a relaxation mechanism for T1 in the rotating frame in native and immobilized protein solutions.
abstract: T1 relaxation in the rotating frame (T1rho) is a sensitive magnetic resonance imaging (MRI) contrast for acute brain insults. Biophysical mechanisms affecting T1rho relaxation rate (R1rho) and R1rho dispersion (dependency of R1rho on the spin-lock field) were studied in protein solutions by varying their chemical environment and pH in native, heat-denatured, and glutaraldehyde (GA) cross-linked samples. Low pH strongly reduced R1rho in heat-denatured phantoms displaying proton resonances from a number of side-chain chemical groups in high-resolution 1H NMR spectra. At pH of 5.5, R1rho dispersion was completely absent. In contrast, in the GA-treated phantoms with very few NMR visible side chain groups, acidic pH showed virtually no effect on R1rho. The present data point to a crucial role of proton exchange on R1rho and R1rho dispersion in immobilized protein solution mimicking tissue relaxation properties.
authors.affiliation: National Bio-NMR Facility, University of Kuopio, Kuopio, FIN-70211, Finland.
authors.forename: H I
authors.initials: HI
authors.lastname: Mäkelä
authors.forename: O H
authors.initials: OH
authors.lastname: Gröhn
authors.forename: M I
authors.initials: MI
authors.lastname: Kettunen
authors.forename: R A
authors.initials: RA
authors.lastname: Kauppinen
mesh_terms: D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002545:Brain Ischemia / Q000378:metabolism; D002417:Cattle; D003432:Cross-Linking Reagents; D005976:Glutaral; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D019047:Phantoms, Imaging; D011489:Protein Denaturation; D011506:Proteins / Q000737:chemistry*; D011522:Protons; D012710:Serum Albumin, Bovine / Q000737:chemistry; D012996:Solutions
chemical_list: D003432:Cross-Linking Reagents; D011506:Proteins; D011522:Protons; D012996:Solutions; D012710:Serum Albumin, Bovine; D005976:Glutaral