222 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



I'hodopsin. Hagins worked with the excised eyes of all)ino rabbits, pre- 

 viously dark-adapted, and measured the brightness of a monochromatic 

 light beam reflected out of the eye and into a photomultiplier tube. The 

 visual pigments were excited by a flash of light obtained by discharging 

 energy, stored in capacitors, across a spark gap built into a xenon filled 

 tube. The changing intensity of the reflected monochromatic light beam 

 following the 20 fxsec. light flash was displayed on an oscillograph. The 



ABSORBANCE(lcm) • 0.245 



-10 



X 



u 



4 

 UJ 



366 



405 436 \ 546/ 579 



X mji. 



— — 15 p MCOOd* 



75 



... 175 " 



— • — I minute 



• « 



\ / 



Fig. 1. Difference sjieetra of degassed rhodopsin .solutions after flash excitation in 

 a 5-cm absorption cell. The times indicated are the intervals between beginning of the 

 exciting flash and beginning of the analyzing flash. The wave lengths indicated are 

 obtained from a mercury arc spectrum photographed on the same plate. The ordinate 

 is in relative units: to convert ordinate to actual change in absorbance of the solution, 

 multiply by 0.043. 



preliminary results published to date show a detectable reduction in al)- 

 sorption of the reflected monochromatic beam when the wave length is 

 486 m/x. The reduction in absorption follows a characteristic exponential 

 time course which, at 12°C, has a half-time of 20 msec, and at 26°C has 

 a half-time of 1 msec. Thus, this visual process, which Hagins believes to 

 be the disappearance of the intermediate state metarhodopsin (7), is 

 markedly affected by temperature. 



The work in our own laboratory has been with aqueous digitonin solu- 

 tions of cattle rhodopsin which were subjected to two consecutive flashes; 

 the first flash is a high energy flash (400 joules) to excite the pigment 



