The fractional electron transfers at both the hydrogen bonded interfaces have been realized from the density redistribution. The detailed analysis of the sTD-DFT simulated absorption spectra (fig. and SI section 1.4) provides a deeper understanding towards the modifications to electronic structure of each component involved in electronic communication of the hCBS. To compare the absorption spectra of the components with the complete model system, we have considered the PLP and α-helix 8 into a single component instead of considering them as separate. Heme Soret band transition, the most important spectral feature in porphyrin based systems, is dependent on the oxidation state of iron. Experimentally reported absorption spectra of Fe(III)-CBS exhibits a Soret peak at 428 nm. In our calculated spectra of the Heme model (fig. In the spectra of the complete model (fig. )), the Heme soret band transitions were found to be red shifted as compared to Heme model shown in fig. ). In the presence of PLP-α-helix 8, the occupied molecular orbitals of the Heme get more delocalized within the porphyrin macrocycle (fig. (a) and (c) and S5), which results in the red shift of the Soret band of the Heme. This phenomenon can be attributed to the fact that the electronic redistribution due the hydrogen bonding between Cys52 and Arg266 leads to an increase in conjugation length of the π electrons of the Heme. On the other hand, π → π * transitions of PLP were found to be blue shifted as compared to the PLP-α-helix 8 model shown in fig. ) and fig. . The comparison of the major transitions, in terms of the energies of the frontier molecular orbitals, is given in the fig. and SI section 4. The observed spectral shifts in the complete system as compared to the corresponding components clearly indicate that the electronic states of the Heme and PLP are coupled via the hydrogen bond network discussed earlier.