Molecular biology and genetic engineering technology have become nowadays crucial in pharmaceutical industries. Point mutations are introduced in proteins in order to get novel specific drugs which additionally would show antiviral and antibacterial resistance. Mutated proteins cause very often serious health disorders. It is known that the function of protein complexes depend not only on their structure but also on their flexibility [1- 6]. Moreover, the protein flexibility may influence action of a prosthetic group important for a proper protein functioning. We will present how point mutations in the vicinity of the iron-quinone complex (Fe-Q) in bacterial reaction centers isolated from Rb.sphaeroides resulting in changes of the Fe-Q hydrophobicity, modify the rigidity of the iron bonds and its spin and valence states. It is known that for the efficient action of the reaction centers the non-heme iron should be in a high spin ferrous state. Mössbauer spectroscopy was applied to monitor a local flexibility of the protein system and the iron states [5, 7, 8]. The obtained results we will compare with the flexibility of the whole protein core observed by using neutron scattering [9]. Our studies concern mutated photosynthetic complexes but the results clearly demonstrate that changes of protein flexibility may be used for modulation of the protein therapeutic efficiency.