CaptAvidin™ biotin-binding protein contains a nitrated tyrosine in its biotin-binding site. This chemical modification permits dissociation of the avidin-biotin complex under milder conditions than the traditional avidin-biotin complex. At pH 4.0, CaptAvidin™ biotin-binding protein binds biotin tightly with a K_a of ∼10⁹M^-1. This association can then be reversed at pH 10, allowing complete dissociation of the avidin-biotin complex. This is in contrast to the harsh conditions (8 M guanidine hydrochloride, pH 1.5) needed to dissociate the avidin-biotin complex.