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Zahradnikova, A., M. Dura, I. Gyorke, A. L. Escobar, I. Zahradnik, and S. Gyorke. Regulation of dynamic behavior of cardiac ryanodine receptor by [Mg.sup.2.sup.+] under simulated physiological conditions. Am J Physiol Cell Physiol 285: C1059--C1070, 2003. First published July 2, 2003; 10.1152/ ajpcell.00118.2003.--[Mg.sup.2.sup.+], an important constituent of the intracellular milieu in cardiac myocytes, is known to inhibit ryanodine receptor (RyR) [Ca.sup.2.sup.+] release channels by competing with [Ca.sup.2.sup.+] at the cytosolic activation sites of the channel. However, the significance of this competition for local, dynamic [Ca.sup.2.sup.+]-signaling processes thought to govern cardiac excitation-contraction (EC) coupling remains largely unknown. In the present study, [Ca.sup.2.sup.+] stimuli of different waveforms (i.e., sustained and brief) were generated by photolysis of the caged [Ca.sup.2.sup.+] compound nitrophenyl (NP)-EGTA. The evoked RyR activity was measured in planar lipid bilayers in the presence of 0.6-1.3 mM free [Mg.sup.2.sup.+] at the background of 3 mM total ATP in the presence or absence of 1 mM luminal [Ca.sup.2.sup.+].[Mg.sup.2.sup.+] dramatically slowed the rate of activation of RyRs in response to sustained ([greater than or equal to]10-ms) elevations in [Ca.sup.2.sup.+] concentration. Paradoxically, [Mg.sup.2.sup.+] had no measurable impact on the kinetics of the RyR response induced by physiologically relevant, brief ( excitation-contraction coupling; cardiac myocytes; magnesium; calcium signaling

The structure of DR1199 protein isolated from the radio-resistant bacterium Deinococcus radiodurans was determined to gain insight into its function and the role in response to irradiation and oxidative stress. The results revealed that DR1199 might function as a general stress protein involved in the detoxification of the cell from oxygen reactive species rather than as a peptidase in D. radiodurans.

Analytical ultracentrifugation and electron microscopy studies have showed that the PH1527 protein from Pyrococcus horikoshii encodes a 39014 Da protein and shares the characteristic tetrahedral shape of Haloarcula marismortui TET (HmTET) and PhDAP in solution. The specificity, the mode of action, and the enzymatic activity of the PhTET2 complex from Pyrococcus horikoshii are discussed.