Rotating frame spin—lattice relaxation in solid hydrated methaemoglobin

✍ Scribed by D.D. Eley; M.J. Hey; A.J.I. Ward

• Publisher: Elsevier Science
• Year: 1978
• Tongue: English
• Weight: 341 KB
• Volume: 58
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(78)80283-8

✦ Synopsis

Proton 7-1~ relation times in two sampks of methaemogIobiin with different 'sifter wntents showed t&t a process occurs vrith a correhtion time of the order le sat 240 K-This is probably an exchange of moIecufes between bound and free vater.

In a previous paper [I] we reported the temperature dependence of water proton NMR relaxation times (T, and T2) in some samples of iyophilized bo-vine methaemoglobin which had been rehydrated to different extents. A shallow mirtimum in TI arcund 230 K showed that there was a broad distriiution of correlation times present which was centred around 2 ns at that temperature and which was probably due to the reorientation of water molecules aEected by interactions with the protein. The T, data at low temperatures were simiIarly interpret&d but a levelling off observed at higher temperatures pointed to an additional relaxation mechanism becoming significant. The temperature at which this effect became apparent depended on the water content, being lowest for the samples with the hi&& water contents. A simiktr observation has been made for the keratin-water system by Lynch and Marsden [2] who attributed it to an exchange of protons between protein chains and water molecules. This would allow rapid relaxation in the protein to contribute to the measured relaxation rate for the water protons. We have now extended our experiments to in&de Tr measurements with spin-loc&g rf fields (H,) of I .&G and 2.6 G corresponding to radial frequencies of 4-3 X IU4 and 7-O X I@ rad s-t respectiveIy_ _A minimum observed in TIP as 'Je temperature was varied aIlowed the correlation time to be determined for a process which occurs with a frequency of the order IO5 Hz when the TI process has a frequency of IO9 Hz. We