3-DIMENSIONAL H-1-TOCSY-RELAYED CT-[C-13,H-1]-HMQC FOR AROMATIC SPIN SYSTEM-IDENTIFICATION IN UNIFORMLY C-13-LABELED PROTEINS

Three-dimensional H-1-TOCSY-relayed ct-[C-13,H-1]-HMQC is a novel expe riment for aromatic spin system identification in uniformly C-13-label ed proteins, which is implemented so that it correlates the chemical s hift of a given aromatic proton with those of the directly attached ca rbon and all vicinal protons. The ct-HMQC scheme is used both for over lay of the indirect H-1 and C-13 chemical shift evolution periods and for the generation of H-1-H-1 antiphase magnetization to accelerate th e H-1-TOCSY magnetization transfer at short mixing times. As an illust ration, data recorded for the 18 kDa protein cyclophilin A are present ed. Since transverse relaxation of C-13-H-1 zero-quantum and double-qu antum coherences is to first order insensitive to C-13-H-1 heteronucle ar dipolar relaxation, the new experiment should work also for protein s with molecular weights above 20 kDa.