Thioether Formation of Phycocyanobilin: A Model Reaction of Phycocyanin Biosynthesis

Abstract

Abstract The reaction of phycocyanobilin dim ethylester (1 a) with ethanethiol is studied. The spectral shifts during a slow reaction correspond to the disappearance of the double bonds at the ethylidene group (595 → 580 nm) and at the methine bridge between rings B and C (365 → 395 nm). Chromic acid degradation of the reaction products reveiles that the thiol has been added at the ethylidene double bond yielding two stereoisomers as expected. The reaction is considered as a model reaction for the presumed last step of phycocyanin biosynthesis, namely the formation of the thioether between cysteine residues of the apoprotein and phycocyanobilin.