Hydrolysis of nucleoside phosphates. Part 10. Comparison of the metal ion facilitated hydrolysis for the 5'-triphosphates of 1,N6-ethenoadenosine (.epsilon.-ATP), adenosine (ATP), and cytidine (CTP). Dephosphorylation of .epsilon.-ATP proceeding with zinc(2+) and copper(2+) via structurally different species: evidence for a long-sought, monomeric, back-bound complex with copper(2+)/.epsilon.-ATP