- Michael Hammerling 19:10, 5 March 2012 (EST) I'd be interested to know what membrane pumps are light-activated, and how these work? It seems a lot more straightforward for a channel to be light-activated through a conformation change than a pump to my intuition. It could cause a conformation change that allows it to cleave ATP, I suppose. Also, just have to bring up this paper. They use in silico feedback and light-activatable transcription factors to fine-tune expression level in E. coli. This seems like a lot more promising route than trying to "program" the desired behavior into a circuit. 
- David M. Truong 19:33, 17 March 2012 (EDT): Halorhodopsin, bacteriorhodopsin, proteorhodopsin, sensory rhodopsin I, and phoborhodopsin are known light-activated ion pumps. In bacteriorhodopsin, the retinal initiates a cascade of proton transfers through aspartate residues from the intracellular face out to the extracellular space, thereby pumping protons out of the cell. Photon absorption by bacteriorhodopsin isomerizes retinal from an all-trans to 13-cis conformation, raising the pK (dissociation constant) of the protonated schiff base. In the 13-cis conformation, a proton is then released to an aspartate in the proton release complex, and finally pushed into the extracellular space. To renew this process, a new proton is accepted at the extracellular space, shuttled via aspartate residues back to the retinal schiff base and reverting it to an all-trans state, where it is ready for the next cycle of photon absorption. [proton cycling] Halorhodopsin acts similarly, but slightly differently in that, it accepts a chloride ion into it's core and instead of deprotonation, a chloride takes its place. Proteorhodopsin's act similar to bacteriorhdopsin and can be used to generate ATP. 
- Milias2011 pmid=22057053
- Yizhar2011 pmid=21363959
//Microbial opsins: a family of single-component tools for optical control of neural activity.