Although microsomal P450s represent the majority of P450s, only microbial P
450s have been amenable to crystal structure solution. We have recently sol
ved the first crystal structure of a microsomal P450, 2C5, a progesterone h
ydroxylase from rabbit. We discuss the features of the protein in common wi
th existing structures of microbial P450s and limitations of homology model
ing mammalian P450s based on the microbial structures. Unique features invo
lving membrane, substrate and cytochrome P450 reductase interactions are al
so discussed. (C) 2000 Elsevier Science S.A. All rights reserved.