NMR-STUDY OF THE POSITIONS OF HIS-12 AND HIS-119 IN THE RIBONUCLEASE-A URIDINE VANADATE COMPLEX

The binding of uridine vanadate to ribonuclease A has been investigate d by one- and two-dimensional H-1 NMR. The homonuclear Nuclear Overhau ser and exchange spectroscopy spectrum of the uridine vanadate/RNase A complex exhibits cross peaks between both the C5H and C6H protons of uridine vanadate and the H epsilon 1 proton of His-12 of ribonuclease A, These cross peaks suggest that the H epsilon 1 proton of His-12 is in the vicinity of the uracil base of uridine vanadate, as observed in the crystallographic structure of the uridine vanadate/RNase A comple x. However, no cross peaks are observed between the C,H and C,H proton s of uridine vanadate and the H epsilon 1 proton of His-1 19 of ribonu clease A, although they were predicted based upon the distances calcul ated from coordinates of the crystallographic structure of the complex . These results suggest that there is a significant difference between the positioning of the His-1 19 side chain in the solution and in the crystallographic structures.