Effects of zinc on the activity and conformational changes of arginine kinase and its intermediate.

The effects of zinc on arginine kinase and its collapsed-state intermediate were studied. Both arginine kinase and the collapsed-state intermediate were inactivated in the presence of zinc, following a biphasic kinetic course. The corresponding apparent rate constants of inactivation at different zinc concentrations and conformational changes in the presence of 0.5 mM zinc were obtained. The conformational changes of arginine kinase and the collapsed-state intermediate were followed by fluorescence spectra and circular dichroism spectra. Comparison of the results for arginine kinase and the collapsed-state intermediate showed that the collapsed-state intermediate was more susceptible to zinc, which indicated that the collapsed-state intermediate was more flexible and unstable than arginine kinase. The special structure of arginine kinase might explain these diverse phenomena.