This is a big thing that has been boiling in my head. With Orochimaru in the Akatsuki that makes nine. I think the Original Teams were in teams of three. The Three Strongest who were the higher uppers and two partys after that. The party Orochimaru was in was Orochimaru, Itachi, and Kisame. Orochimaru who was a member of the Konoha village having previous experience with the Sharingan knew that he was in good hands having Itachi as a partner. But Jealousy rose maybe because of several things. I. Itachi might have copied some of Orochimaru's High Level Jutsu's. II. Orochimaru might have seen Itachi do something extremely vicious and wreckless. III. Itachi used the Tsukiyomi on Orochimaru hoping to make it evolve. These are all logical. Seeing that in this team Orochimaru would get alot of face time with Itachi and his abilities. Orochimaru on his search for every jutsu would be intrigued at definately getting his hands on the Tsukiyomi and the Amaterasu.