Biosynthesis of retinoic acid by intestinal enzymes of the rat

Abstract

The incubation of Β-carotene-14C with the soluble fraction of the intestinal mucosa resulted in the formation of small amounts of acidic material. The addition of NAD or NADH to the soluble fraction caused a tenfold increase in this material. Incubation of retinal-15-14C with the soluble fraction of the intestinal mucosa plus NAD or NADH resulted in the conversion of 80-90% of the retinal to acidic material, which has been shown to contain retinoic acid.In vivo studies on the formation of retinoic acid in the intestinal mucosa after the administration of Β-carotene-14C revealed that an appreciable amount of Β-carotene was converted to acidic compounds. When retinal-15-14C was administered, portal blood contained 30-40% of the absorbed radioactivity. 24% of this radioactivity was found in acidic material, which has been shown to contain retinoic acid.It is suggested that enzymes in rat intestine cleave Β-carotene to retinal and oxidize the latter to retinoic acid, which is then transported via the portal circulation to the liver.

Keywords

• Β-carotene
• cleavage
• retinal
• oxidation
• retinoic acid
• biosynthesis