(ăk′tĭ-vā″tor)
[Pronunciation]

1. A substance in the body that converts an inactive molecule into an active agent, such as the conversion of pepsinogen into pepsin by hydrogen ions.
2. Any substance that specifically induces an activity, such as an inductor or organizer in embryonic development or a trophic hormone.
3. A removable orthodontic appliance that transmits force passively from muscles to the teeth and alveolar process in contact with it.
Also called myofunctional appliance.

Subentry:
urokinase-type plasminogen activator