FACILE MEASUREMENT OF POLYPEPTIDE J(HNH-ALPHA) COUPLING-CONSTANTS FROM HMQC-J SPECTRA

A method, based on linewidth measurements, is described which permits the rapid and facile determination of J(HNH alpha) coupling constants from N-15 labeled proteins. Using appropriately processed KMQC-J data, we have found that a simple linear relationship exists between the ha lf-height linewidth (Delta v(1/2)) of N-15-H-1 cross peaks and their c orresponding J(HNH alpha) coupling constants. Tests indicate that this technique permits the accurate measurement of up to 100 J(HNH alpha) coupling constants in less than 30 min. Furthermore, the J(HNH alpha) measurements Can be done manually - without the need of any computer-b ased curve-fitting or minimization. Comparisons between J(HNH alpha) v alues predicted from high resolution X-ray structures and those determ ined using this technique indicate that the method is both accurate an d precise (correlation coefficient = 0.90, rmsd = 0.75 Hz).