The ω-hydroxylation of prostaglandins, fatty acids and eicosanokts are catalyzed by members of cytochrome P4504A subfamily. Cytochrome P4504A4 (CYP4A4), a member of this subfamily, was first purified from pregnant rabbit lung (Williams ef a/, 1984) and concurrently from progesterone-treated rabbit lungs (Yamamoto ef a/, 1984). The induction of 4A4 in pregnant rabbit lung suggests that it is of physiological importance although the precise function is not known. CYP4A4 has been expressed in E. coll and a purification system, which provides detergent free enzyme, developed. Kinetics for this expressed enzyme with the physiologically significant substrates prostaglandin E1, (PGE,) and arachidomc acid have been examined in the presence and absence of cytochrome bs (cyt b5). PGE1 metabolism by CYP4A4 displays at least a 2-fold increase in activity on addition of cyt b5 to the assay system (Turnover No. +cyt b5= 206 min-1; -cyt b5= 77.6 min-1) while metabolism of arachidonic acid by CYP4A4 is only detectable in the presence of cyt b5 (Turnover No. +cyt b5= 204 min-1). A haem-deplete form of cyt b5 (apo b5) has been prepared to further examine the cause of CYP4A4 stimulation by cyt b5. Until recently stimulation of P450 activity by cyt bs was thought to be due to improved electron transfer. However, Guengrich el al (1996) has shown that stimulation of some P450s is not dependent on electron transfer to cyt b5. Initial data suggest that the apo b5 stimulates CYP4A4 metabolism (Turnover No. PGE, +apo b5 =166 min-1). (Supported by NIH Grant No.:GM31296 to BSSM.).
|Original language||English (US)|
|State||Published - Dec 1 1998|
ASJC Scopus subject areas
- Molecular Biology