Dirigent protein

Dirigent protein is a protein which dictates the stereochemistry of a compound synthetised by other proteins. They are enzymes catalyzing the coupling of two radicals. Dirigent proteins are found in plants. Originally they were discovered in coniferous trees, were they participate in lignan biosynthesis. Lignan synthesis is catalysed by oxidative enzymes. In the test tube the reaction results in a heteregenous mixture of compounds. When dirigent protein is present during the reaction, only one stereoisomer of one compound is produced. Dirigent proteins possess no oxidative radical forming activity of their own; but catalyze a radical radical coupling. Thus they shall be regarded as enzymes. According to a disputed theory dirigents also participate in the synthesis of lignin, a polymer with some similarity to ligninans. However, lignin is optically inactive, and this theory is now regarded as disproven. A few scientists believe that the lignin polymer itself may posses dirigent protein activity.