RESUMEN
Conditions for the optimal expression of the human CYP1B1 hemoprotein in Escherichia coli have been investigated. CYP1B1 cDNA was prepared from a retinal cDNA template and used to generate cDNA fragments with modified 5'-sequences reported to allow enhanced expression in E. coli DH5alpha. Plasmids were constructed, using the pCWori+ expression vector and were used to examine necessity for thiamine, delta-aminolevulinic acid (ALA), and IPTG. The optimal shaking speed in an orbital incubator was 150 rpm at 30 degrees C. Higher speeds resulted in increased cell death and lower speeds resulted in lower expression of cytochrome P450. IPTG was necessary for this expression system, which makes use of the lac repressor, but levels above 0.5 mM were without additional benefit. We were able to show thiamine to be unnecessary in this expression system, although included by others expressing CYP1B1. ALA has been reported to enhance expression of several different forms of cytochrome P450. We examined the dependence of CYP1B1 expression on ALA. The expression proved to be highly dependent upon this heme precursor, with levels of CYP1B1 increasing approximately 20-fold, to 920 nmol/l in the presence of up to 2.5 mM ALA. The question of whether heme synthesis and apoprotein synthesis were coupled was then investigated. It could be shown that although heme synthesis was not limiting (CYP101 holoenzyme expression in the absence of ALA was four times higher than the ALA-supported CYP1B1 holoenzyme expression), it was necessary for optimal expression of CYP1B1. CYP1B1 protein synthesis appears to be coupled to heme precursor availability, as seen by SDS-PAGE, because in the absence of heme precursor apocytochrome P450 1B1 does not accumulate.