Parliament's Public Accounts Committee (PAC) on Thursday postponed its sitting after SEBI chairperson Madhabi Puri Buch and other officials expressed inability to attend the meeting, panel chairperson K C Venugopal said.Buch, under a cloud over allegations of conflict of interest levelled by US-based short-seller Hindenburg, was asked to appear before the PAC, which is reviewing the performance of the market regulator..