CAROTENOID EXCITED STATE DYNAMICS IN THE ORANGE CAROTENOID PROTEIN FROM CYANOBACTERIA

摘要

A water-soluble orange carotenoid protein (OCP), was first identified in 1981 (Holt & Krogmann 1981), and its crystal structure was solved recently to 2.1 A resolution (Kerfeld et al 2003). The high-resolution structure revealed that the protein is ahomodimer. Each 35kDa subunit contains a single molecule of 3'-hydroxyechinenone (hECN); this carotenoid has a conjugation length of N=12 and contains a conjugated carbonyl group. The OCP is presumed to play a role in photoprotection, since transcript levels for the protein increase during exposure to intense light (Hihara et al 2001). The OCP can also be converted to a red form, called the RCP, which is characterized by a red-shifted absorption spectrum (Kerfeld et al 2003). The function of RCP is notknown, but it has a higher rate of singlet oxygen quenching, most likely due to increased solvent accessibility.