BIOSYNTHESIS OF VITAMIN A WITH RAT INTESTINAL ENZYMES.

Vitamin A is synthesized from beta-carotene in cell-free homogenates of rat intestinal mucosa, the biosynthetic enzymatic activity being present in the soluble protein fraction of the homogenate. Also required are a heat-stable factor in the particulate fraction, molecular oxygen, and bile salts. The reaction is stimulated by glutathione. The product, obtained in yields of up to 50 percent, has been identified as vitamin A aldehyde (retinal) by way of its semicarbazone derivative. The reaction mechanism involves the central cleavage of beta-carotene into two molecules of retinal.