[en] In an attempt to understand how to switch off the quarternary structure of the protein modulates the response of the iron-binding site, the iron K-edge spectrum (measured by XANES spectroscopy) was used to investigate the iron structure of hemoglobin. The strong variation of ligand-binding properties with pH for carp hemoglobin is not reflected in the electronic distribution of the heme-iron. It can be supposed that hemoglobin affinity is directly controlled by the protein and not by some particular changes of the iron atom. (Auth.)