I was reading about Cas1 and Cas2 and came across this excerpt:
...Cas2 was identified as a metal-dependent endoribonuclease that cleaves ssRNA or dsDNA...
What does metal-dependent mean in this context?
It means that these enzymes need a metal ion as a co-factor for their function. This metal ion is typically bound somewhere near or in the active center and helps stabilizing transition states.
Without these metals, these enzymes cannot function properly, that's why chelating agents are used in protein or DNA preparations to inhibit their function.