VOL. 12 (1953) 



CO COMPOUNDS OF RESPIRATORY ENZYMES 



293 



First, the photodissociation is accomplished by illuminating the cell suspension 

 with yellow light, for example, the 589 m/i line of the Na arc or the 578 m/x of the Hg arc, 

 other portions of the spectrum of these line sources being readily eliminated by appro- 

 priate filters having the characteristics shown in Fig. 3. The observation of the photo- 

 dissociation of CO compounds is made in the region of the Soret band (410-480 m/x) and 

 the photocell is rendered insensitive to the yellow light not only by the nature of its 

 surface (Cs-Sb) but also by the blue colour filter combination shown by the solid curve 

 of Fig. 3. 



'°° 1 C - 3480 



700 



A(m;j) 



Fig. 3. Transmission curves for optical filters used to isolate photodissociating light (above 520 m/n) 



from spectrophotometric wavelengths (410-480 m/i). C represents Corning glass filters, W represents 



Wratten filter, and B + L represents Bausch and Lomb interference filters (MD-27). 



MONOCHROMATOR 

 set to /\. 



Exit sht 



MONOCHROMATOR 

 set to T^p 



7-\ Vibrating mirror 



*V :_'; / Color filters 



Cell (Blue' 



/." 



xit slit 



suspension 



:D:::::::i:p-^-^v.g: 



(Entronce 

 ^ slit 



Ptiotocell 



AC Amplifier 



i> 



o 



Tungsten lomp 



=■<- Yellow filter 

 •«-Shutter 



^^\*- Sodium ore 

 Kj) ;\=589m^ 



Half silvered mirror 



Fig. 4. A schematic diagram of a double-beam spectrophotometer suitable for measuring the kinetics 

 of the photochemical decomposition of the CO compounds of the respiratory enzymes within intact 

 cells. The characteristics of the optical filters are given in Fig. 3. The wavelengths Aa and Ab are 



set in the region 410-480 mju (MD-28). 



Secondly, as Fig. 4 shows, the differential double-beam spectrophotometer em- 

 ploys two wavelengths of light, one a reference wavelength, for example 480 m/x where 

 no appreciable optical density changes due to photodissociation are to be expected, and 

 the other an adjustable wavelength (in the region 410-480 mix). The photoelectric cir- 

 cuit measures the differences of the light transmission changes at the two wavelengths, 

 and this difference is not affected by leakage of yellow light through the colour filters. 



Thirdly, to discriminate further against light leakage, the two beams of monochro- 

 matic light are chopped by a vibrating mirror at 60 cps so that first one and then the 

 other is incident upon the sample and the photocell. Thus the output current from the 

 photocell consists of a square 60 cps wave, the amplitude of which represents the dif- 

 ference of light transmission at the two wavelengths of light^. Since the arc lamps for 



References p. 2971298. 



