ace turn card and a donk bet into my KK

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Villian is loose and can be aggressive and I have no read on the third player in this hand.

It would be tough to put villian on a 2 since he limped utg but 22 and most Ax would be within in his range.

Party Poker 2/4 Hold'em (10 handed) converter

Preflop: Hero is MP2 with K[img]/images/graemlins/spade.gif[/img], K[img]/images/graemlins/heart.gif[/img].
<font color="#666666">3 folds</font>, MP1 calls, <font color="#CC3333">Hero raises</font>, <font color="#666666">2 folds</font>, Button calls, <font color="#666666">2 folds</font>, MP1 calls.

Flop: (7.50 SB) 3[img]/images/graemlins/diamond.gif[/img], 5[img]/images/graemlins/club.gif[/img], 4[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(3 players)</font>
MP1 checks, <font color="#CC3333">Hero bets</font>, Button calls, MP1 calls.

Turn: (5.25 BB) A[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(3 players)</font>
<font color="#CC3333">MP1 bets</font> Hero???