The interaction of direct electric current (dc) and proteins is a little explored topic. We had reported that exposure of Crotalus atrox venom to dc caused irreversible inactivation of phospholipase A(2) and metalloprotease and that the eukaryote adenylate kinases (AK) precipitate in nondenaturing gel electrophoresis. AK1 displays an elevated percent difference of CHarged versus POlar amino acid content (CH-PO 14). Commercial AK1 and other 17 enzymes with various CH-PO values were exposed in solution to dc (0-0.7 mA) from low voltage (0-10 V), then enzymatic activity was assayed. The enzymes with CH-PO higher than 10.0 were irreversibly inactivated by current exposure; those with CH-PO between +3 and -5 were not. Inactivation was dependent on the ionic strength of the medium and not on the net charge of the protein. Circular dichroic spectroscopy showed a structural modification in some of the inactivated enzymes. CH-PO could be a crucial, although rough, parameter for predicting protein inactivation by low-voltage exposure. The observed effect seems due to the current density. Enzymatic activity maybe a more accurate sensor of conformational changes than circular dichroism spectroscopy. A better understanding of efficacy of many electrical devices utilized in medical practice may follow.