Int J Biochem. 1993 Dec;25(12):1775-84.  

Identification of a microsomal retinoic acid synthase as a microsomal cytochrome
P-450-linked monooxygenase system.

Tomita S, Tsujita M, Matsuo Y, Yubisui T, Ichikawa Y.

Department of Biochemistry, Kagawa Medical School, Japan.

1. To characterize an enzyme which metabolizes retinal in liver microsomes,
several properties of the enzymatic reaction from retinal to retinoic acid were
investigated using rabbit liver microsomes. 2. The maximum pH of the reaction in
the liver microsomes was 7.6. 3. The Km and Vmax values for all-trans, 9-cis and
13-cis-retinals were determined. 4. The reaction proceeded in the presence of
NADPH and molecular oxygen. 5. The incorporation of one atom of molecular oxygen
into retinal was confirmed by using oxygen-18, showing that the reaction
comprised monooxygenation, not dehydrogenation. 6. The monooxygenase activity
was inhibited by carbon monoxide, phenylisocyanide and anti-NADPH-cytochrome
P-450 reductase IgG, but not by anti-cytochrome b5 IgG. 7. The enzymatic
activity inhibited by carbon monoxide was photoreversibly restored by light of a
wavelength of around 450 nm. 8. The retinal-induced spectra of liver microsomes
with three isomeric retinals were type I spectra. 9. The microsomal
monooxygenase activity induced by phenobarbital or ethanol were more effective
than that by 3-methylcholanthrene, clotrimazole or beta-naphthoflavone. 10.
These results showed that the monooxygenase reaction from retinal to retinoic
acid in liver microsomes is catalyzed by a cytochrome P-450-linked monooxygenase
system.

PMID: 8138015 [PubMed - indexed for MEDLINE]