Hydroxylation of Prostaglandin A₁ by the Microsomes of Rabbit Intestinal Mucosa

抄録

Microsomes from rabbit small intestine mucosa were found to catalyze the hydroxylation of PGA₁ in the presence of NADPH. The major product was identified as 20-hydroxy PGA₁ by using high performance liquid chromatography and gas chromatography-mass spectrometry, and the minor product was assumed to be 19-hydroxy PGA₁. The ratio of the former product to the latter was about 24.1. The specific PGA₁ ω-hydroxylase activity of small intestine microsomes was comparable to that of liver microsomes, and was significantly higher than those of microsomes from other tissues such as kidney cortex and lung. Microsomes from rabbit colon mucosa also catalyzed the hydroxylation of PGA₁ in the presence of NADPH, with the ratio of ω- to (ω-1)-hydroxy PGA₁ formed being 33.0. The PGA₁ hydroxylase activities of the microsomes from both small intestine and colon were inhibited markedly by carbon monoxide, indicating the participation of cytochrome P-450. A cytochrome P-450 was solubilized from small intestine microsomes, and purified to a specific content of 10.5 nmol of cytochrome P-450/mg of protein. This cytochrome hydroxylated PGA₁ at the ω-position with a turnover rate of 38.2 nmol/min/nmol of cytochrome P-450 in the reconstituted system containing cytochrome P-450, NADPH-cytochrome P-450 reductase, cytochrome b₅ and phosphatidylcholine. It is suggested that this cytochrome P-450 is specialized for the ω-hydroxylation of PGA₁ in small intestine microsomes.