296 



B, CHANCE, L. SMITH, L. CASTOR 



VOL. 12 (1953) 



430-445m;j — 

 logIo/I = O.OIO 



T" 



10 



20 

 Seconds 



30 



40 



Fig. 

 and 



8. The kinetics of photodissociation 

 recombination of the cytochrome 



homogenates, bakers' yeast cells, A. pasteurianmn, and Bacillus suhtilis^^, and find £5^^^, 

 = 12 cm-^ X mil/"i fQj- lY^Q cytochromes of type a^. (Reference 14 gives detailed data 

 on the experimental controls and also the method 

 of calculating the results.) 



In our previous studies the sensitivity of 

 the apparatus was insufficient to give any quan- 

 titative idea of the molecular extinction coef- 

 ficients of the "CO-binding pigment" of S. albus. 

 We now have increased the sensitivity, and satis- 

 factory kinetic data may be obtained as in Fig. 8. 

 A preliminary value can be given for the molecu- 

 lar extinction coefficient of the band at 546 m/u, 

 £ = 5 cm-i X milf-i, about half that of the 

 value for myoglobm-CO at 580 m/x (10.6 cm"^ 

 X mil/~^)^2. The extinction coefficient at 589 m^u 

 is very small compared to that of the yeast enzyme and this emphasizes the difference be- 

 tween this CO-binding pigment and cytochrome a.j. 



The photochemical action spectrum 



One of us (L. C.) has recently developed an appa- 

 ratus for measuring photochemical action spectra 

 in a drop of bacterial suspension by means of the 

 platinum microelectrode^^. This method utilizes the 

 steady-state system developed by Connelly and 

 Brink^^ in their studies of the respiration of nerve. 

 A steady-state in oxygen tension results from the 

 balance between inward diffusion of oxygen and 

 utilization of oxygen by the nerve tissue. The same 



fitg-CO compound in bakers' yeast cells as 

 measured by the method of Fig. 4 (Expt. 

 measured by the method of Fig. 4. Il- 

 luminating light is 589 m/^ (Expt. 144). 



Fig. g. The kinetics of photodissocia- 

 tion and recombination of "CO-binding 

 pigment" in a suspension of S/«/5/;v/o- 

 coccus albus cells as measured by the 

 method of Fig. 4. Illuminating light is 

 578 m^< (Expt. 144). 



conditions obtain in a drop of bacterial or yeast sus- 

 pension respiring in a CO-Og atmosphere. The size of 

 the drop, the number of cells, and the substrate concen- 

 tration are adjusted so that the steady-state oxygen 

 concentration for maximal effectiveness of the photo- 

 chemical reaction is obtained. Illumination of the drop 

 will displace this steady-state and the change of oxygen 

 concentration is sensitively recorded by the platinum 

 microelectrode. 



Our results for S. albus show a Sorct band at 418 

 m/i. definitely displaced from the 430 m/x peak measured 

 for 3^east cells with the same apparatus. A preliminary 

 action spectrum for the respiratory enzyme in S. albus 

 in the vSoret region is shown in Fig. 10. 



In the visible region of the spectrum, the peaks 

 of the CO compound are found to lie at 535 and 566 mjLt 

 in fairly good agreement with the peaks of the absorp- 

 tion difference spectrum that lie at 535 and 570 m^Li^^. 

 These values are similar to those for hemop^rotcins 



References p. 2gyl2g8. 



420 440 



Fig. 10. A relative photochemical 

 action spectrum of the CO-binding 

 pigment in Staphylococcus albus. 

 Similar data are readily obtained 

 in the visible region of the spectrum 

 (-'.5'^) (0-38). 



