Heterologous expression systems have proven to be very important in P4
50 research, permitting investigation of many P450s identified only by
recombinant (cloning) technologies. They also make it possible to stu
dy human P450s since tissue sources for naturally occurring enzymes ar
e difficult to obtain. A variety of different heterologous systems hav
e been applied to the study of P450s and each one has its own unique a
dvantages. For the study of biophysical properties and structure/funct
ion relationships, E. coli has proven to be a particularly good system
. Both microsomal and mitochondrial P450s can be expressed to high lev
els in E. coli and subsequently purified to homogeneity for detailed a
nalysis. Techniques of both site directed mutagenesis and random chime
ragenesis are very facile in bacteria providing excellent opportunity
to analyze specific aspects of structure/function relationships of P45
0s. Furthermore microsomal P450s are active in intact E. coli, activit
ies being supported by flavodoxin and flavodoxin reductase, providing
the opportunity to develop bioreactors expressing designer P450s. The
salient features of P450 expression in bacteria are summarized herein.