Biotin-avidin system

Avidin-biotinic system as the aid of address delivery of antitumor compounds 98MI54. 

More detailed discussions of avidin-biotin systems as well as the process of adding a biotin affinity group to proteins, nucleic acids, and other biomolecules can be found in Chapters 11 and 23. 

Figure 22.21 Antibodies may be conjugated to liposomes using an indirect approach incorporating a (strept)avidin-biotin system. Biotinylated liposomes may be complexed with biotinylated antibodies using (strept)avidin as a bridging molecule or may be complexed with an antibody-(strept)avidin conjugate.

In a recent study of the avidin-biotin system Wang et al.41 have used the LIE approach as well as a version of it that includes an extra entropy term . That is, the interaction free energy in the bound and free states was... 

Fig. 1. Schematic drawing of various immune methods for localization of antigens. (A) Direct method. (B) Indirect method. (C) Immunogold with silver enhancement. (D) Peroxidase-antiperoxidase method. (E) Avidin-biotin system.

The above represent the past and present of the most common enzyme-mediated methods of antigen detection. There are alternate procedures available, involving such methods as antibiotin antibody steps that combine the avidin-biotin systems with a further antibiotin/antienzyme sandwich for still greater sensitivity. Also, there are methods that follow a PAP procedure with a biotinylated antibody to the PAP immunoglobulin followed by ABC detection (15). The obvious problem created with this approach is the tremendous... 

Although many applications of avidin-biotin systems have been developed so far the nature and mechanism of the tight binding are not yet fully understood. It... 

In 1989, to the best of our knowledge, the first report appeared on the use of an avidin-biotin system for the immobilization of enzymes in the preparation of biosensors. Walt et al. have immobilized biotin-modified enzymes (urease, esterase, and penicillinase) on the surface of biotin-modified optical fiber using avidin as a binder (Figure 5a). They have demonstrated the general use of this procedure in immobilizing several types of enzymes. At nearly the same time, Gunaratna and Wilson used an enzyme column in which choline esterase and choline oxidase were immobilized through avidin-biotin complexation for the determination of acetyl-... 

The following procedure is based on the Vectastain ABC kit from Vector (suppliers appendix). It uses an avidin-biotin complex to attach horseradish peroxidase (HRP) or alkaline phosphatase (AP) to the biotinylated secondary antibody. Avidin-biotin systems are capable of extremely high sensitivity because multiple reporter enzymes are bound to each secondary antibody. In addition, the detergent Tween 20 is a popular alternative to protein blocking agents when using nitrocellulose or PVDF membranes. 

TTBS is well suited for avidin-biotin systems. For nylon, protein binding agents are recommended. Because nonfat dry milk contains residual biotin that will interfere with the immunoassay, its use must be restricted to the blocking step only. 

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