Longitudinal relaxation (T1) measurements for all lines (α-CH, β-CH, O-CH3) in the 4-methoxypyridine 1H-NMR spectrum were used to study the interaction of 4-methoxypyridine with purified microsomal cytochrome P-450 from livers of phenobarbital-treated rats. The paramagnetic contribution to the observed T1 −1 value was determined from its dependence on 4-methoxypyridine concentration. In the P-450-4-methoxypyridine complex the latter is oriented so that the nitrogen of pyridine is directed towards the Fe3+.
