DTNB Inactivation Rates of PR-AMP Cyclohydrolase and the Effect of PR-AMP and Mg2. Data are as follows A. (△) 2.7×10−3 min−1, control no DTNB, (○) 8.5×10−2 min−1, 212 μM DTNB, (▲)1.82 x10−2 min−1, 212 μM DTNB with 1.0 mM PR-AMP; B. (◆) 2.7×10−3 min−1, control no DTNB, (○) 1.6×10−2 min−1, in the absence of Mg2+, 424 μM DTNB, (■) 2.5×10−1 min−1, 424 μM DTNB.