[en] Simultaneous commutation relations for remaining axial second-class current in the weak interaction are obtained. On their basis derived is the sum rule expressing axial formfactor of the second-class current through isovector electromagnetic formfactor and axial formfactor of the first-class current. Single- and multiparticle contribution in the sum rule obtained are taken into account. Obtained are modifications of sum rules for structural functions, describing inelastic scattering of neutrinos and electrons on hadron targets. Problems in calibration theories, arising while introducing second-class currents, are discussed