Science: Lasers illuminate chemistry of vision

2019-03-03 03:05:02

By JIM BAGGOTT For more than 20 years, chemists have known that the first step in vision involves a fast chemical reaction initiated by light. Now researchers in the US have used very short pulses of light to determine just how fast this reaction is. They have found that it occurs in 200 million billionths of a second, making it one of the fastest reactions ever observed experimentally (Science, vol 254, p 412). Researchers from the University of California’s chemistry department and its Lawrence Berkeley Laboratory studied rhodopsin, extracted from bulls’ eyes. The molecule is made up of a protein and a long-chain molecule called retinalis, and is found in some cells of the retina. When retinalis absorbs a photon of light, it twists around a carbon-carbon double bond in the chain. This is the first step in a convoluted series of biochemical changes which turn light into an electrical signal which is passed to the brain along the length of the optic nerve. The American chemists were able to study the reaction because of recent developments in ultrafast lasers. The reaction was so quick that it challenges the traditional picture of how photochemical reactions occur,