George Wald Biography (1906-1997)
A born and bred New Yorker, George Wald graduated from New York University in1927 and received his Ph.D. five years later from Columbia University. For the next two years, Wald studied in Europe, working with two of the continent's most eminent chemists, Berlin's Otto Warburg and, in Zurich, Switzerland, Paul Karrer (1889-1971), a pioneer in vitamin A research. He then returned tothe United States and, in 1934, joined the faculty of Harvard University, where he remained for the rest of his career.
From the start, Wald was primarily interested in the photochemistry of vision. In 1933, he had already discovered that vitamin A was a vital ingredient inthe eye's retina, specifically in the pigments contained in the retina's rods and cones. The rods--the tiny rod-shaped cells that allow the eye to see indim light--contained a pigment called rhodopsin. What exactly was the relationship between rhodopsin and the vitamin A it contained? Wald wasn't certainbut during his first quarter century at Harvard, he and his co-workers, in particular, Paul K. Brown (1919- ), did their best to find out.
The group's first task was to break down rhodopsin--until then, generally considered one large, lumpy, and exceedingly complicated molecule--into its component parts. Rhodopsin, Wald soon demonstrated, was in reality composed of two substances: a colorless protein, opsin, and a yellow carotenoid, retinal (or retinene) that was actually the aldehyde form of vitamin A. Rhodopsin's role in the visual cycle was a crucial one. When stimulated by light rays, Wald discovered, the rhodopsin molecule promptly splits into its twocomponent parts and the retinal fraction is transformed back into vitamin Aby an enzyme. In the dark, the process is reversed: vitamin A becomes retinal, the components come back together and once again form rhodopsin. Most important of all: the various biochemical changes trigger an electrical activity that excites both the retina's nerves and the optic nerve resulting in vision.
In the course of working out this complex scenario, Wald answered the question that had long puzzled scientists: why is night blindness an early sign of vitamin A deficiency? Because, Wald explained, as the light-dark changes takeplace, some retinal is invariably lost and more must be formed from the body's supply of vitamin A. If, over time, this supply becomes exhausted, no moreretinal can be made, the rods no longer function normally--and the eye no longer sees in dim light. In the 1950s and 1960s, Wald and his Harvard associates went on to identify the pigments in the retina's cones--all also related tovitamin A--that detect red, yellow-green and blue light and showed how the absence of one of these pigments can result in color blindness. For these andhis earlier discoveries, Wald shared the Nobel Prize in physiology and medicine in 1967.