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.
Sinsheimer Laboratories, Department of Chemistry and Biochemistry, University of California, Santa Cruz 95064.
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Yang
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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