The most abundant cation and osmolyte in the cytoplasm of E. coli, K+, has been used in studies of molecular interactions of DNA, proteins, ribosome and ions via 39K NMR. In our previous experiments, a large transverse relaxation rate of 39K has been observed in dense slurries of E. coli cells. Since the interaction of the K nucleus with the surrounding electric field gradient of the DNA dominants the 39K transverse relaxation in a K-DNA solution with little salt added, it was considered as the explanation for the 39K relaxation measured in vivo. However, the relaxation rate of 39K in DNA solutions, even with a very high concentration (i.e., physiological conditions), is much slower than that in vivo. Similar results were obtained for concentrated K-BSA and KCl solutions. The only in vitro solution that gives rise to the same large magnitude of the transverse relaxation rate as in vivo are ribosome solutions, the highly negative charged ribosome particles that have the most nucleic acids in the cell. Therefore, ribosome particles are considered as the key element that enhances the transverse relaxation of 39K in vivo. The similar characteristic of transverse relaxation was also observed in 23Na-ribosome solutions. These results require further experimental studies to confirm and to explore the molecular nature of the ribosome particle and K+, Na+-ribosome interactions. We will be using the DMX 400 spectrometer with the 10mm BB probe for both 39K and 23Na (a more sensitive nucleus) NMR studies.
Showing the most recent 10 out of 613 publications
