Those two electrons left over form a double bond, a pi bond. And so he formed the fumerate that contains the double bond between these two carbons. And these two H atoms then bind onto the carrier Flaving adenine dinucleotide to form the Fadh two. Now, one important fact that you have to know about Succinate dehydrogenase is, unlike the enzymes that we discussed so far, this enzyme, Succinate dehydrogenase, is actually part of the inner mitochondrial matrix. In fact, it's an iron sulfur protein that is also part of the electron transport chain. So what actually happens is when the Sad well, first of all, the Sad is covalently attached onto the Succinate dehydrogenase.