Help with left pan code

Hey, ive made a little 360 pan in flash with 2 buttons left pan and right pan. the pan image is in a MC (panClip1) and moves via a large motion tween.

the right button code is:

on (press) {
_root.panClip1.gotoAndPlay(_root.panClip1._currentframe);
}

the left button code is:

on (press) {
_root.leftpan = true;
}

also the code on the clip is…

//EnterFrame Event
onClipEvent (enterFrame) {

if (_root.leftpan == true) {
if( _root.panClip1._currentframe == 1)
{
_global.toggleplay = false;
}
frame = this._currentframe -1
this.gotoAndStop (frame);
}
}

i want the left button to do the same but when the tween gets to frame 1 it just stops… how can i say… if the frame = 1 then go to and play the end frame(400).