BESSEL KOK AND GEORGE HOCH 



409 



observed signal) on rate constants, light intensities, total pigment 

 concentration (Ptot.) '»"<^l '^ '^ proportionality factor correlated with 

 Beer's law. Fig. 8, which is based on this lornuila, predicts the pat- 

 tern of observations for a variety of intensities of detecting beam (700 

 m^) and actinic beam (absorbed by accessory pigment). Actual ex- 

 perimental findings agree with this pattern (17). The most signi- 

 ficant aspect is that at a certain value of the detecting intensity the 

 activating light induces no effects. 



The implication is that two light steps, and at least one dark step, 

 nuist be involved in the behavior of "P 700." 



Effects of Various Agents on the Two Light Effects 



One, of course, would like to obtain more knowledge about the 

 chemical nature of the 700 m^ pigment and the reactions involved in 

 its turnover. Table 2 shows the influence of various agents and treat- 

 ments on the two absorption shifts as observed with the difference 

 apparatus. 



The negative light effect, i.e., the photochemical bleaching and 

 spontaneous dark regeneration, appears very stable and is only slightly 

 affected by any of the inhibitors employed. In cell-free Anacystis 



M 



' '^2'^4 



I Act 



•^b^'^S^D 



0<f + kj^) + (kj+k3)Iy 



Fig 8. Expected dependence of sign and magnitude of the background absorp- 

 tion changes at 700 m^ as a function of detecting intensities /„ (700 m/i) and 

 actinic intensity /^ (600 m/x) in Anacystis. (Experimental data in 1/). 



