F keys (F1, F2, etc) do not control Pro Tools.
In later versions of OSX, the F keys may default to controlling aspects of the operating system ans user interface (volume, brightness, etc). To change this, do the following:
1. Go to the Apple Menu->System Preferences->Keyboard.
2. In the Keyboard tab, Check the box that says "Use all F1, F2, etc. keys as standard function keys"
3. Close System Preferences.
The F keys should now control Pro Tools as expected.