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    Determination of the effective correlation time modulating 1H NMR relaxation processes of bound water in protein solutions
    (Elsevier Science Inc, 2008) Yilmaz, Ali; Budak, Hatice; Ulak, F. Sadan
    The relaxation in protein solutions has mainly been studied by nuclear magnetic relaxation dispersion (NMRD) techniques. NMRD data have mostly been analyzed in terms of fast chemical exchange of water between free water and water bound to proteins. Several approaches were used for the estimation of correlation time modulating the relaxation mechanism of bound water. On the other hand, in a nuclear magnetic resonance experiment, the relaxation rates of protein solutions (1/T-1 and 1/T-2) and also those of free water (1/T-1f and 1/T-2f) are measurable. However, the relaxation rates of bound water (1/T-1b and 1/T-2b) are not. Despite this, equating (1/T-1-1/T-1f)/2(1/T-2-1/T-2f) to (1/T-1b)/2(1/T-2b) leads to an expression involving only an effective T that is related to the rotational correlation time (tau(r)) of proteins. Equating the ratios may therefore give a simple alternative method for the determination of tau(r) even if this method is limited to a single resonance frequency. In this work, a formula was derived for the solution of the effective tau. Then, the 1/T-1 and 1/T-2 in solutions of two globular proteins (lysozyme and albumin) and one nonglobular protein (gamma-globulin) were measured for different amounts of each protein. Next, the values of 1/T-1 and 1/T-2 were plotted vs. protein concentrations, and then the slopes of the fits were used in the derived equation for determining the effective tau values. Finally, the rotational correlation time tau(r), calculated from tau, was used in the Stokes-Einstein relation to reproduce relevant radii. The effective tau values of lysozyme, albumin and gamma-globulin were found to be 5.89 ns, 7.03 ns and 8.8 its, respectively. tau(r) values of albumin and lysozyme produce their Stokes radii. The present data suggest that use of the measurable ratio in the derived formula may give a simple way for the determination of the correlation times of lysozyme and albumin. (C) 2008 Elsevier Inc. All rights reserved.
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    Öğe
    EPR studies of gamma-irradiated L-alanine ethyl ester hydrochloride, L-arginine and alanyl-L-glutamine
    (Taylor & Francis Ltd, 2008) Aydin, Murat; Baskan, M. Halim; Yakar, Sedat; Ulak, F. Sadan; Aydinol, Mahmut; Aydinol, Belkis; Bueyuem, Muharrem
    gamma-Irradiated powders of L-alanine ethyl ester hydrochloride (LAES), L-arginine (LA) and alanyl L-glutamine (ALG) were investigated at room temperature by electron paramagnetic resonance (EPR). The observed species in LAES and LA are attributed to the CH3CHCOOC2H5 and CH2CHNHCNHNH2 radicals, respectively. In the case of ALG, the EPR signal is attributed to the CH2CNHCOOH. Hyperfine structure constants and g-values are determined for these three radicals. It is found that these results are in good agreement with those of previous experimental and theoretical studies. The unirradiated samples were found to display no EPR signal.
  • [ X ]
    Öğe
    NMR Proton Spin-Lattice Relaxation Mechanism in D2O Solutions of Albumin Determined at 400 MHz
    (Springer, 2014) Yilmaz, A.; Zengin, B.; Ulak, F. Sadan
    T-1 values in pure D2O and D2O solutions of human serum albumin (HSA) were measured versus temperature. A formula was derived based on H-H interactions between the surface HDO and non-exchangeable protein protons. The formula was used to evaluate the average distance of the interactions (rav). The effective correlation times were then derived by replacing the experimental data in the formula. Short correlation times obtained for the solution with low HSA (0.02 g albumin for one ml of D2O) decreased from 53 to 29 ps, while longer times increased from 1.19 to 2.22 ns. They are of the order of a fraction of a nanosecond for the solution with high HSA (0.08 g albumin per one ml of D2O). The perfect consistency between the derived theory and experimental data indicates that the high-field 1/T-1 in D2O solutions of albumin is caused by dipolar interactions between the surface HDO and non-exchangeable protein protons. It also suggests that the effective correlation time of the surface HDO is of the order of the mean lifetime of short-lived surface water.