USE OF A BIOSENSOR WITH SURFACE-PLASMON RESONANCE DETECTION FOR THE DETERMINATION OF BINDING CONSTANTS - MEASUREMENT OF INTERLEUKIN-6 BINDING TO THE SOLUBLE INTERLEUKIN-6 RECEPTOR

The interaction of recombinant human interleukin-6 (IL-6) with the sol uble extracellular form of its receptor (sIL-6R) has been characterize d by the application of expressions developed for quantitative affinit y chromatography to results obtained with a biosensor based on surface plasmon resonance detection. First, the interaction of sIL-6R with IL -6 covalently attached to the biosensor-chip was characterized from th e dependence of the surface plasmon resonance response upon the concen tration of receptor injected into the biosensor. A binding constant fo r the interaction between sIL-6R and IL-6 was then determined from the biosensor response observed for mixtures of IL-6 and receptor-a proce dure that is shown to provide unequivocal characterization of the comp eting reaction, irrespective of the model used to describe the biphasi c interaction between partitioning receptor and immobilized IL-6. A bi nding constant of 5 x 10(7) M(-1) has been obtained for the interactio n of sIL-6R with two equivalent and independent sites on an essentiall y dimeric IL-6 preparation produced using the pUC vector system, and a lso for the interaction of sIL-6R with a monomeric IL-6 preparation th at was univalent in its interaction with receptor.