An experiment is presented which allows for the sensitivity-enhanced measurement of proton exchange rates in a HSQC type experiment. Instead of using INEPT type transfer of magnetization from protons to heteronuclei and vice versa, we have used heteronuclear Hartmann-Hahn transfer, which is known to have higher sensitivity in the presence of chemical exchange. Direct NOE's between NH protons and α-protons are suppressed by an exchange-editing step unless the α-resonances are degenerate with the water resonance. A comparison between the exchange-edited HEHAHA-HSQC and a standard exchange-edited HSQC experiment performed on the uniformly 15N-labeled staphylococcal nuclease H124L shows an enhancement of approximately 100% with the former experiment. A set of one-dimensional exchange-edited spectra of urea was used for evaluating the ability to extract exchange rates using the presented experiment.
Bibliographical noteFunding Information:
We are grateful to Professor John L. Markley for providing the sample of 15N-labeled staphylococcal nuclease H124L. Partial support of this work comes from the NIH Grant DK18778 to I.M.A.
K.Z. thanks the Austrian Fonds zur Förderung der wissenschaftlichen For-schung for an Erwin Schrödinger Fellowship (Project J-01393CHE). NMR instrumentation was provided with funds from the NSF (BIR-961477) and the University of Minnesota, Medical School, and we are grateful to Dr. David H. Live, who expertly manages and maintains these NMR facilities.