Fraction of energy, E em /E0, transferred to the electron-photon component of EAS at E0 = 1015 ± 1019 eV was estimated by using the Cherenkov radiation data and the data on charged particles obtained at the Yakutsk EAS array. The results are compared with predictions of different models for energy dissipation into the EAS electron-photon component and with calculations performed with different primary nuclei content. In the energy ranges 1015 ± 1016 eV and 1018 ± 1019 eV , the ratio E em /E0 is equal to (77 ± 2)% and (88 ± 2)%, respectively, that does not contradict to a mixed composition of primary particles in the first energy interval and purely proton composition in the second one.