3.F.2.  The Light-driven Calcium Ion Transporter (L-CAT) Family

Active transport is driven by light-induced electron transfer in a photoactive molecule that is asymmetrically disposed across a lipid bilayer (Bennett et al. 2002). The system comprises a synthetic, light-driven transmembrane Ca²⁺ pump based on a redox-sensitive, lipophilic Ca²⁺-binding shuttle molecule whose function is powered by an intramembrane artificial photosynthetic reaction centre. The resulting structure transports calcium ions across the bilayer of a liposome to develop both a calcium ion concentration gradient and a membrane potential, expanding Mitchell's concept of a redox loop mechanism for protons to include divalent cations. Although the quantum yield is relatively low (approximately 1 per cent), the Ca²⁺ electrochemical potential developed is significant.