The irreversible inhibitors bind covalently to the enzymes and inactivate them. This inactivation is irreversible. These inhibitors are usually toxic substances which maybe man-made or naturally present.
Iodoacetate is an irreversible inhibitor of the enzymes glyceraldehyde 3-phosphate dehydrogenase and papain. It combines with the sulfhydryl groups (-SH) at the active site of these enzymes and renders them ineffective.