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Jack Myers 



two light beams of wavelength X± and complementary wavelength >.2 

 show enhancement. Then in at least one of the 'beams alone the 

 q.uantum yield must be less than maximum simply because quanta are 

 distributed in excess to one of the two photoreactions . Addition 

 of the second beam permits the use of quanta previously wasted and 

 gives a more than additive increase in oxygen evolution. We in- 

 terpret enhancement by this simple extension of the two-photoreac- 

 tion hypothesis. 



A framework for discussion of the distribution problem is pre- 

 sented in Fig. 4. In order to supply the intermediates for ther- 

 mal reactions, it is supposed that photoreactions I and II are 

 required in a stoichiometric ratio, n. One can visualize, for ex- 

 ample, that cyclic phosphorylation may place extra demand on I and 

 a value of n > 1. Hence we cannot now specify a value and must 

 leave n as an unknown in subsequent analysis. 



One point of distribution of quanta is detenained by absorp- 

 tions of the two pigment systems. We define by a the fraction of 

 total absorbed quanta which are absorbed by pigment system 2. A 

 second possible point of quanta distribution occurs within the 

 pigment systems in transfer of quanta to the terminal photorecep- 

 tors (such as P700 for photoreaction l). In this transfer we can 

 imagine two possible arrangements. In the first and simplest we 

 imagine that the two pigment systems are arranged, perhaps spa- 

 tially, so that there is an invariant transfer within each system 

 to its specific photoreceptor. Such an arrangement, suggested by 

 Duysens and Amesz,^ we have called the separate package model. We 

 have also imagined a second possible arrangement called the spill - 

 over model. In this we envision that quanta absorbed by system 2 

 (largely composed of accessory pigments) are transferred preferen- 

 tially to the photoreceptor for II, but also may be transferred to 

 the photoreceptor for I if II is "full." Reasons for considering 

 the spillover model have been discussed previously.^® It is not 

 a novel concept, having been considered, at least in principle, 

 by W. A. Arnold, by Hans Gaffron (personal communications), and 

 probably also by others. 



In short, there are now two alternate models for quanta dis- 

 tribution. The separate package model supposes that the distri- 

 bution at any wavelength is governed only by absorption into the 

 two pigment systems. The spillover model requires a two-stage 

 distribution system, the first by pigment absorption ratios and 

 the second in energy transfer between pigments. Actually the two 

 models merely describe limit possibilities. For example, if 

 energy transfer can occur between system 2 and photoreaction I 



