I got this from another forum....and it works like a charm.
If the lever is switched to AEL/AFL position and you press the focus button, the camera does the focus/exposure (or both) lock. According to the GR user guide, the default [AEL/AFL setting] is focus lock. So if you prefer to use the AE lock, change the [AEL/AFL Setting] to AEL.
Now if you press the focus button, the camera should lock the exposure. By default, the AE/AF lock is kept as long as you hold the focus button. Luckily, there is an option in the camera menu to change this behavior. The [AEL/AFL Lock Setting] has two options...
Off - the lock is kept as long as you hold the focus button (default setting)
On - first press of focus button locks the focus/exposure, the second press cancels the lock.