摘要：

Formation of an intramolecular cross-link in enzyme donor polypeptide fragments of &bgr;-galactosidase, thereby forming a cyclic enzyme donor which is hindered from complementation with an enzyme acceptor fragment to form active of &bgr;-galactosidase. The cyclic enzyme donor can be linearized by cleaving to restore complementation ability. Assays in which such cyclic enzyme donors are linearized by specific analytes are disclosed, as well as novel homobifunctional bis- maleimido cross-linking agents of the formula ##STR1## wherein R is hydroxy or acetate.

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