Phycobiliproteins streptavidin

The spectral properties of four major phycobiliproteins used as fluorescent labels can be found in Tables 9.1 and 9.2. The bilin content of these proteins ranges from a low of four prosthetic groups in C-phycocyanin to the 34 groups of B- and R-phycoerythrin. Phycoerythrin derivatives, therefore, can be used to create the most intensely fluorescent probes possible using these proteins. The fluorescent yield of the most luminescent phycobiliprotein molecule is equivalent to about 30 fluoresceins or 100 rhodamine molecules. Streptavidin-phycoerythrin conjugates, for example, have been used to detect as little as 100 biotinylated antibodies bound to receptor proteins per cell (Zola et al., 1990). 

Other proteins commonly cross-linked to avidin or streptavidin are chromogenic or fluorescent molecules, such as ferritin or phycobiliproteins (Chapter 8, Section 1.7). These conjugates can be used in microscopy techniques to stain and localize certain antigens or receptors in cells or tissue sections. 

Conjugates of avidin or streptavidin with these fluorescent probes may be prepared by activation of the phycobiliprotein with SPDP to create a sulfhydryl-reactive derivative, followed by modification of avidin or streptavidin with 2-iminothiolane or SATA (Chapter 1, Section 4.1) to create the free sulfhydryl groups necessary for conjugation. The protocol for SATA modification of avidin or streptavidin can be found in Section... 

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