Using an optical biosensor Biacore 3000 the interaction of human recombinant cytokeratins (CK) with isatin analogues (5-aminocaproyl-isatin and 5-aminoisatin) immobilized on the CM-5 chip has been investigated. CK-14 effectively interacted with 5-aminocaproyl-isatin immobilized on the carboxymethyl dextran chip surface, but not with a "shorter" analogue (5-aminoisatin). In contrast to CK14 CK8 effectively interacted only with 5-aminoisatin. In both cases cytokeratin binding with the immobilized isatin analogues was characterized by rather high affinity (Kd of 0.7 microM for the pair CK14/immobilized 5-aminocaproylisatin and 1.7 microM for the pair CK8/immobilized 5-aminoisatin). CK20 did not interact with both immobilized isatin analogues. Taking into consideration non-specific binding of mouse CK14 and rat CK8 with 5-aminocaproyl-Sepharose we have performed comparative analysis of amino acid sequences of human, mouse, and rat CK8 and CK14. The data obtained suggest that in the case of human, mouse, and rat CK14 the N-terminal domain is the most variable among these species, whereas the major differences between amino acid sequences of human, mouse, and rat CK8 have been found both in N-terminal and C-terminal regions.