TIME SEQUENCE OF REACTIONS 



185 



eter that employs two light beams differing slightly in wavelength. 

 These results allow us to determine, on a kinetic basis, the sequence 

 of reactions in the respiratory chain that follows infrared illumina- 

 tion. 



METHOD 



In our spectrophotometric methods, the "compensating" beam 

 passes over an optical path identical to that of the measuring beam 



Fig. 1. A double-beam spectrophotometer for recording differences of optical 

 density at two wavelengths selected so as to maximize the response to the oxida- 

 tion and reduction of the cytochromes and minimize the response to nonspecific 

 effects. This apparatus employs Bausch and Lomb grating monochromators in- 

 stead of the Beckman quartz monochromators used in previous experiments. 



