Ion selective electrode estimation of avidin and biotin using a lysozyme label

A method for the homogeneous estimation of the biotin binding protein, avidin, by use of an enzyme label is described. As in homogeneous enzyme immunoassay, where no separation step is employed, the activity of a biotin-lysozyme conjugate is inhibited by the binding of avidin, instead of an immunoagent. Biotin concentration can also be related to conjugate activity after sequential saturation of a known amount of avidin by the biotin sample and the biotin-lysozyme conjugate. Conjugate activity is followed potentiometrically by the release of trimethylphenylammonium ion from loaded Micrococcus lysodeikticus cells or turbidimetrically using a M. lysodeikticus cell suspension.