Complex sentence: Although the functionality of the heme in succinate dehydrogenase is still being researched, some studies have asserted that the the first electron delivered to ubiquinone via (3Fe-4S) may tunnel back and forth between the heme and the ubiquinone intermediate.
Split into simpler sentences: Although the functionality of the heme in succinate dehydrogenase is still being researched, some studies have been completed and assertions made. As stated earlier, the first electron delivered to ubiquinone via (3Fe-4S) may tunnel back and forth between the heme and the ubiquinone intermediate.