In this study, on the DNA binding domain of the γ δ resolvase, has been reported a physicalchemical method to calculate the backbone dihedral angles φ of a given polypeptide chain starting from the amino acid sequence. Calculations are based on the MMF method which focuses on the development of mechanical forces after the establishment of precise chemical interactions among the side chains of the residues. To define the occurring chemical interactions it was necessary, in turn, to define rules in order to calculate the partial twistings for each interaction occurred; then, for a given residue, all the partial twistings were added up in order to calculate the dihedral angle φ. The rules reported in the section Methods concern the twisting constants (former degrees of freedom ) and the distances for the chemical interactions to occur. Twisting constants have been reported to be fundamental for the determination of the folding factors and the latter to be, in turn, a fundamental physical measure for the calculation of dihedral angles. Anyway, in the previous study, the definition of the twisting constants was described as the main limit of the whole work . At this purpose, this work has been realized with the aim to define univocally the twisting constants in order to allow, in the end, the precise calculation of the backbone dihedral angles, specifically the backbone dihedral angles φ. With the rules proposed on the twisting constants, as well as on the threshold distances for the chemical interactions, the backbone dihedral angles φ of 1res have been calculated and then compared to the values experimentally obtained by NMR . A comparison between the two sets of data is shown in Figure and can be seen that 38 calculated values, out of 42, show a good agreement with the experimental data , whereas only 2 values have a weak agreement (φ18 and φ25) and just 2 calculated values (φ21 and φ42) do not match the experimental data. This results make the method proposed a good tool to determine and predict at least the backbone dihedral angles φ of polypeptides, even if, further improvements will be realized studying other polypeptides.