When both K m and V max are altered, Is the enzyme inhibited or activated?

Enzyme activators lower K (the Michaelis constant) and/or raise V (the asymptotic reaction velocity at infinite substrate concentration); conversely, inhibitors raise K and/or lower V . But what if an effector moves both K and V in the same direction? Uncompetitive inhibitors, which decrease both K and V by the same factor, are the most common example of this. A less well-known example occurs often when crowding agents are added to the buffer in order to mimic the environment commonly encountered in vivo. Crowding agents tested on different enzymes have been shown to have every conceivable effect on K or V , causing them to rise, fall, or stay the same. In this article, a mathematical analysis is presented allowing biochemists to judge whether an effector that causes K and V to both move in the same direction serves as an inhibitor, an activator, or most surprising, as both. © 2019 International Union of Biochemistry and Molecular Biology, 2019.