H-1-NMR CHEMICAL-SHIFT CALCULATION OF ALPHA-CH AND NH PROTONS IN BASIC PANCREATIC TRYPSIN-INHIBITOR

H-1 NMR chemical shifts of alpha-CH and NH protons in Basic Pancreatic Trypsin Inhibitor (BPTI) were calculated theoretically on the basis of the atomic coordinates obtained from X-ray diffraction. The alpha-CH chemical shifts were calculated with ring current effects and magnetic anisotropy effects of C = O bonds. By adding the diamagnetic term to these two effects, the NH chemical shifts were calculated. The agreement between observed and calculated chemical shifts for alpha-CH and NH protons of BPTI was good, although the difference between calculated and observed values for the NH proton was larger than that for the alpha-CH proton. The presence of a hydrogen bond involving the NH proton of Lys-46 was proposed in solution in contrast to the case of crystalline states on the basis of the chemical shift calculation, which was supported experimentally from solution NMR.