Yes, I would fold the turn. He has something, you don't, so your only hope is a bluff, but even this is only likely to work if he has x9. Assuming he doesn't have a 4 (and he could have, he's repping one), you only have 8 outs; if he does have one you're drawing dead.

I hate rivers like this. You are only ahead if he has slowplayed a pair of kings, basically, which is certainly possible at this level. But he could have AK (considering his PF raise), A4 or K9 (if he's a donk), 44 (though I doubt it), even AA. I suspect I would check behind here - you're beaten maybe 60% of the time?