Iridoid Synthase (IMAGE) John Innes Centre Caption The biosynthesis of iridoids, a class of bicyclic monoterpenes, features an atypical cyclization reaction catalyzed by iridoid synthase (ISY). Crystallographic and biochemical characterization of ISY from Catharanthus roseus provides insights into the ISY enzymatic mechanism and highlights similarities with the homologous progesterone 5β-reductase. Credit The John Innes Centre Usage Restrictions Credit the John Innes Centre License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.