Step four is the second oxidative decarboxylation step of the citric acid cycle. And this is catalyzed by alpha ketoglutrade dehydrogenase, also an allosteric enzyme. So remember back to our discussion that this is actually step four. In step four, we take the alpha key to gluterate produced in step three, and we basically kick off a carbon dioxide molecule and replace it with coenzyme A to form submit coenzyme A, we also oxidize the alpha ketoglutrate and reduce the NAD plus into NADH. And here's our carbon dioxide molecule. So alpha ketoglutrade catalyzes the second oxidative decarboxylation step.