TPTK OOP for big pot early in tourney

[ras52]

The first level of a Live $40 NLHE tourney, blinds 25/50. 22 players remaining from 24, with 8 at my table. My stack is 2650, having started with 3000. I have A[img]/images/graemlins/spade.gif[/img]K[img]/images/graemlins/spade.gif[/img] in UTG+1 and raise to 150, getting 4 callers: MP, Button (both good players, have won a few pots and have me comfortably covered) and both blinds (unknown) - pot 750, my stack is 2500.

Flop A-5-2 rainbow. It's checked to me, I bet 500, MP folds, Button dwells a while then calls, blinds fold - pot 1750, I have 2000 remaining.

Turn T.

What now? My thoughts are that checking would invite a steal, but betting puts me close to being pot-committed, and it's too early to risk an exit with TPTK.

The feasible hands I don't like are A-T, 5-5 and possibly A-5s or A-2s. Without a flush draw on the flop I don't imagine him calling any other A-Xs. Hands I'm beating that would call pre- and post-flop might be A-Q, A-J. I'm quite new to thinking in ranges - and usually end up doing it after the event - so any help there would be welcome. Thanks!