Cis-trans Isomers of Vitamin A and Retinene in Vision

Abstract

Four isomers of vit. A occur in appreciable quantities. Exptl. evidence indicates that the precursor of the visual pigment, rhodopsin, is some cis-isomer of vit. A, probably the [DELTA]3-cis -isomer. In the process of seeing, the retina continuously withdraws the active isomer of vit. A from the circulation and returns to the blood the inactive di-trans-isomer. In this way the visual process is connected intimately with the metabolism and transport of vit. A throughout the body.