VOL. 4 (1950) BIOCHIMICA ET BIOPHYSICA ACTA 215 



THE INTERCONVERSION OF THE RETINENES 

 AND VITAMINS A IN VITRO 



by 



GEORGE WALD* 

 Biological Laboratories of Harvard University, Cambridge, Mass. (U.S.A.) 



In the summer of 1933 I was woiking as a National Research Council Fellow in 

 Otto Meyerhof's Institute in Heidelberg, measuring the distribution of phosphates in 

 the frog retina in light and darkness. I had noticed that the trichloracetic acid used 

 to extract the phosphates turned the red colour of the dark adapted retina to bright 

 orange, and that thereafter the retina behaved as a pu indicator, orange in acid and 

 colourless in alkaline solution. Light adapted retinas were colourless under all circum- 

 stances. 



All about us the Third Reich was coming into flower, and the laboratory' remained 

 an island of sanity in a world increasingly committed to unreason and repression. Under 

 the urging of the Society of Animal Friends, led by a retired general, the government 

 of Baden had forbidden the killing of frogs — that is, Geiman frogs; there seemed 

 to be no objection to importing foreign frogs for laboratory use. 



In August, just after Professor Meyerhof and his assistants left on their vacations, 

 and I had all but terminated my phosphate experiments, a large sh'pment of frogs 

 arrived from Hungary. The Diener was prepared to throw them into the Neckar, but 

 it seemed a pity to waste them, and I decided to use them to try to learn something 

 of the orange p^ indicator which results from the destruction of rhodopsin in the retina. 

 It was under these circumstances that I found retinenci, and had a first view of its 

 interplay with vitamin Aj in the rhodopsin cycle. 



It is only within the past few months that the chemistry of these relationships 

 has been clarified. At a key point in this investigation it fell in with the pattern of 

 Meyerhof's classic experiments on the role of cozymase in the lactic fermentation. 

 For cozymase is also the substance which reduces the retinenes to the vitamins A; and 

 to learn this we entered on a line of experiment developed by Meyerhof many years 

 before. 



It is therefore in a double sense that I offer this essay to Otto Meyerhof: first, 

 for his personal connection with its beginnings ; and again, for the debt to him and to 

 his work which I share with all who do biochemistry. 



retinenEj and vitamin Ai 



Vision in dim light is mediated in all vertebrates through the retinal receptors 

 known as rods. In land and sea vertebrates, these organs contain the red, light-sensitive 



* The recent investigations described in this paper have been supported in part by the Medical 

 Sciences Division of the Office of Naval Research. 



References p. 228. 



