Relaxation-matrix formalism for rotating-frame spin-lattice proton NMR relaxation and magnetization transfer in the presence of an off-resonance irradiation field.
The derivation of a generalized relaxation matrix equation for the off-resonance rotating-frame spin-lattice experiment, representing N macromolecular components, is presented. The applicability of the derived formalism was demonstrated using water proton off-resonance rotating-frame spin-lattice relaxation data obtained for calf lens cortical and nuclear homogenates, a tissue system characterized by the presence of both mobile and solid-like protein domains, whose relative amounts vary in a protein-concentration-dependent manner. Protein concentration and temperature were utilized as variables in the magnetization-transfer experiments. Curve fitting to obtain the relevant magnetization-transfer parameters was accomplished by simulated annealing and the method of steepest descents. In all cases, the best fit, as reflected by the smallest root-mean-square deviation, was obtained by assuming the presence of three components representing bulk-water and mobile and solid-like macromolecular components, characterized by Lorentzian (water and mobile protein) and Gaussian proton resonance lineshapes (solid-like protein). A two-component relaxation model gave unsatisfactory fits. Dilution of nuclear homogenate resulted in physically realistic changes in the derived magnetization-transfer parameters, which included a decrease in the fraction of solid-like protein, in agreement with previously published 13C NMR studies. Changes in magnetization-transfer parameters occurred as a result of the cold cataract phase transition in nuclear homogenate. The utility and limitations of the derived formalism are discussed.
Kuwata
K
K
Sinsheimer Laboratories, Department of Chemistry and Biochemistry, University of California, Santa Cruz 95064.
Brooks
D
D
Yang
H
H
Schleich
T
T
D000818:Animals; D001834:Body Water / Q000378:metabolism; D002417:Cattle; D003459:Crystallins / Q000032:analysis; D007908:Lens, Crystalline / Q000737:chemistry; D046911:Macromolecular Substances; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008280:Magnetics; D008962:Models, Theoretical; D011522:Protons; D014867:Water
D003459:Crystallins; D046911:Macromolecular Substances; D011522:Protons; D014867:Water