The Activity of enzymes are highly regulated in living things. Redox regulation is one of system that regulates enzyme activities. In this system, thioredoxin (Trx) activates or deactivates its target enzymes by transferring electron (e-). In this game, orange- or pink-colored enzymes are activated by Trx, while gray-colored enzymes are deactivated by Trx. When the electron hits orange- or pink-colored enzymes, you earn points. But, when electron hits gray-colored enzymes, you lost points.