Structure of a novel flavin chromophore from Avena coleoptiles, the possible “blue light” photoreceptor

Abstract

A yellow chromophore has been isolated from Avena coleoptiles grown in the dark. It had previously been shown by Zenk [Zenk, M. H. (1967) Z. Pflanzenphysiol. 56, 122–140] to be a flavin of still unidentified structure, and had been suggested to be the blue light photoreceptor in this organism. The structure of this flavin (F1-X) has been identified as 5′-malonylriboflavin by a combination of physicochemical techniques, and by its identity with a sample obtained synthetically. The 5′-malonylester linkage is relatively labile towards hydrolysis and photolysis, it isomerizes to an equilibrium mixture containing probably the 4′ isomer. The electronic spectra of 5′-malonylriboflavin (absorption and fluorescence) are practically identical to those of normal riboflavin (vitamin B₂).