Proton exchange rates from amino acid side chains— implications for image contrast
作者:
Edvards Liepinsh,
Gottfried Otting,
期刊:
Magnetic Resonance in Medicine
(WILEY Available online 1996)
卷期:
Volume 35,
issue 1
页码: 30-42
ISSN:0740-3194
年代: 1996
DOI:10.1002/mrm.1910350106
出版商: Wiley Subscription Services, Inc., A Wiley Company
关键词: magnetization exchange;proton exchange;image contrast;cross‐relaxation
数据来源: WILEY
摘要:
AbstractThe proton exchange rates between water and the hydroxyl protons of threonine, serine, tyrosine, the amino protons of lysine, and the guanidinium protons of arginine were measured in the pH range 0.5 to 8.5 and for the temperatures 4°C, 10°C, 20°C, 30°C, and 36°C. The intrinsic exchange rates of the hydroxyl and amino protons at pH 7.0°C and 36°C were found to be in the range 700 to about 10,000 s−1. In addition, the exchange catalysis by phosphate, carbonate, carboxyl‐, and amino‐groups was investigated. The presence of these exchange catalysts at physiological concentrations increased the proton exchange rates from hydroxyl and amino groups several fold. The proton exchange rates are sufficiently fast that the total magnetization transfer between biomolecules and free bulk water is not rate limited by the proton exchange rate, but by the intramolecular cross‐relaxation rates between the exchangeable and nonexchangeable protons of the biomolecules. Since the cross‐relaxation rates between surface hydration water molecules and biomolecules are usually vanishingly small because of too rapid exchange with the free bulk water, it is proposed that the contrast in MR images is a fingerprint of the number of the exchangeable protons from OH and NH groups of the tissue, as far as the contrast depends on the magnetization transfer between biomol
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