Understanding vision

A discovery at Southampton has answered a fundamental question about the photoreceptor protein known as rhodopsin, which is found in the retina of the eye. The discovery has been the foundation for a body of scientific knowledge which has since underpinned the work of countless biochemists.

The discovery was made in the mid-1960s by a group led by Professor Muhammad Akhtar. He was interested in the structure of rhodopsin, a light-sensitive pigment found in the cells in the retina at the back of the eye. Rhodopsin absorbs light, initiating a sequence of biochemical events that result in a signal being transmitted down the optic nerve to the brain.

Rhodopsin is a protein which contains a form of vitamin A, known as retinal. "The research was motivated by a wish to understand a problem of physical chemistry," says Akhtar. "Retinal does not absorb visible light, so there had to be some sort of ingenious way in which the retinal was modified in order for it to be light-absorbing in the visible range of the spectrum."

Akhtar was the first to solve this problem by determining at a molecular level the nature of the bond between retinal and the protein in bovine rhodopsin. Later he and his team were also the first to describe the structure of rhodopsin in terms of its seven trans-membrane segments; research in other laboratories, using more up-to-date techniques, have since confirmed that this structure is present in all animal rhodopsins studied to date.

The work at Southampton has provided a platform for scientists conducting research into a range of related areas, including investigations into the degenerative eye disease retinitis pigmentosa.

Akhtar's later research led to further findings relating to the molecular mechanism of signal termination, a process through which photo-activated rhodopsin, following the transmission of a visual signal, is modified to bring to an end the signalling event.