To quantify the OLEFs exerted by the protein matrix surrounding M-cofactor of nitrogenase, a protocol inspired by Alexandrova et al.'s was developed. The approach started by extracting FeMoco/FeVco/FeFeco nitrogenase structures collected in the RCSB protein data bank. This initial dataset was filtered based on a series of structural criteria. Firstly, only structures with a resolution ≤ 2.5 Å were retained. Next, we dismissed PDB entries if they a) were determined using CryoEM, b) contained selenium instead of sulfur, c) contained a CO-ligand, d) were crystallized at a non-physiological pH, e) contained xenon or f) were not fully resolved (e.g. due to disorder). Following this filtering, 26 FeMoco, 3 FeVco and 2 FeFeco nitrogenases were retained.