Kühne, Wilhelm

[kü nuh] (1837–1900) German physiologist: discovered reversible photosensitivity of animal eye pigment.

Although Kühne was a medical man, taught by , and a professor of physiology (mainly at Heidelberg), his selection and approach to problems was rather that of a chemist. He worked on trypsin from pancreatic juice and coined the name enzyme (Greek, ‘in yeast’) for the class of ‘ferments’ which activate chemical change in living cells. Other compounds that interested him were proteins; he studied post-mortem change in muscle and found the protein myosin to be the cause of rigor mortis. In the 1860s he separated various types of egg albumen; and when in 1876 F Boll (1849–79) discovered a photosensitive protein pigment in the retina of a frog’s eye, Kühne took up the study of this ‘visual purple’ (now known as rhodopsin) and showed that it is bleached by light and regenerated in the dark. The retina works, he showed, like a renewable photographic plate; he obtained a pattern of crossbars of a window on the retina of a rabbit that had been kept in the dark, exposed to a window and killed. It needed new techniques, in the 1930s, for G Wald (1906–97) and others to advance knowledge of the mode of action of rhodopsin.