However, the structure of E:S appears to be far less rigid than could be expected for such a bulky substrate and sometimes, the substrates are bound less tightly by only one of these residues. This is especially true for DHT, which, due to the different conformation of the ring A from  4 -steroids, does not form a very strong H-bond interaction with Y536 like AD or CHON. The slightly less effective stabilization of enolate is additionally compounded by the lack of a double bond conjugated with the C3 keto group that results in higher charge separation observed in E:I when compared to  4 -unsaturated substrates. These two factors seem to be responsible for the overall increase of G for both barriers and the intermediate product (E:I).