Assesment of protein reorientational diffusion in solution by ¹³C off‐resonance rotating frame spin–lattice relaxation: Effect of polydispersity

Abstract

The 13C off-resonance rotating frame spin-lattice relaxation technique is applicable to the study of protein rotational diffusion behavior in both model in vitro and in vivo systems. The original formalism of James and co-workers [(1978) J. Am. Chem. Soc. 100, 3590-3594] was constrained by the assumption of random isotropic reorientational motion of a monodisperse protein population. Here we extend the formalism to include polydispersity. Application is made to the alkaline pH induced association of lysozyme, lysozyme-bovine serum albumin mixtures, and to the phase separation of lysozyme salt-water mixtures induced by low temperature.

Dynamics of paramagnetic agents by off-resonance rotating frame technique

“…As the results, the relaxivity at high magnetic fields is enhanced. The off-resonance rotating frame is achieved by a long off-resonance pulse as shown in the previous paper [7], which is also a routine sequence used in NMR/MRI for spin saturations or magnetization transfer (MT) [8,9], and for the spin relaxations in the off-resonance rotating frame [10][11][12][13][14]. This sequence contains a long offresonance pulse with duration s and RF amplitude x 1 irradiated at frequency offset D. Under the RF irradiation, the spins are tilted to a h angle, h = tg À1 (x 1 /D).…”

“…Then, the extraction of the dynamic parameters were carried out by analysis of the residual z-magnetization dispersion profiles, which is the residual z-magnetization plotted as a function of frequency offset at fixed RF amplitude. Since the distribution of the equilibrium residual z-magnetization profiles is directly related to the rotating frame relaxation rate constants, thus the dynamic parameters are determined by fitting the profiles with specific kinetic models [10][11][12][13][14]. This method can effectively detect the spins in the motional scale of ps-ls.…”

“…Methods for correlating the residual z-magnetizations of off-resonance rotating frame with the molecular dynamics have been known since 1970s [10][11][12][13][14]. In these studies, spins such as 13 C were used to label the sites so that their residual z-magnetizations directly reflected the dynamics of the molecule at where they were attached.…”

“…In these studies, spins such as 13 C were used to label the sites so that their residual z-magnetizations directly reflected the dynamics of the molecule at where they were attached. Then, the extraction of the dynamic parameters were carried out by analysis of the residual z-magnetization dispersion profiles, which is the residual z-magnetization plotted as a function of frequency offset at fixed RF amplitude.…”

Dynamics of paramagnetic agents by off-resonance rotating frame technique in the presence of magnetization transfer effect

“…However, the off-resonance rotating frame is achieved by the long off-resonance pulse as shown in the previous paper [3], which is the same routine sequence used in NMR/MRI for spin saturations or magnetization transfer (MT) [5][6], and for the spin relaxations in the offresonance rotating frame [7][8][9][10][11]. One of the challenges for the in vivo applications is the interference of magnetization transfer effect [6], which is the dominant relaxation mechanism for the proton spins in tissues under the off-resonance irradiations.…”