<prompt> Irreversible step in citric acid cycle is catalyzed by ?AconitaseSuccinate thiokinasea-ketoglutarate dehydrogenaseIsocitrate dehydrogenase  <response>: Ans. is c i.e., a-ketoglutarate dehydrogenase There are two irreversible steps :oxaloacetate to citrate catalysed by citrate synthase, anda-ketoglutarate to succinyl CoA, catalyzed by a-ketoglutarate dehydrogenase. 