Baculovirus overexpression system

However, other cells may respond differently to the toxin. In particular, platelets are able to resist the entry of pertussis toxin, either because they lack surface binding sites for the toxin B oligomer or because they are unable to internalize the bound toxin (Brass et al., 1990). PT-sensitive G proteins expressed in insect Sf9 cells (ovary cells from the insect Spodoptera frugiperda Sf9 cells are employed as an overexpression system for G proteins and other signal transduction components by infection with recombinant baculovirus) are also not modified by the toxin (Mulheron et al., 1994). 

CMP-neuraminic acid can be used in oligosaccharide synthesis as a substrate for various a2-6-sialyltransferases isolated from rat liver [50] or bovine colostrum [51] as well as a2-3-sialyltransferases isolated from porcine liver [52] and porcine submaxillary glands [53]. Recently, the enzyme has been overexpressed in a baculovirus system [54]. 

Some commercially available phenotyping kits use an array of coumarin analogs designed to be relatively isozyme-specific substrates (probes) that are metabolized to products with easily measurable spectral characteristics. Other commercially available kits use microsomes from baculovirus-infected cells that overexpress individual human GYP isoforms and fluorescent substrates (Vivid substrates) that can be incorporated into 1536 well formats. These simple systems do not readily lend themselves to the in vitro study of enzyme induction, however. The prediction of xenobiotic alteration of the expression of GYP activity in vivo from in vitro experiments will be discussed more completely in the chapter on drug—drug interactions. 

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