65 



John M. Olson and Robert M. Smillie 



given light reaction (e.g. Ri ) . In either Anacystis or Euglena, 

 a photon absorbed by chlorophyll a has a significant probability 

 of driving R^ instead of R, . Analysis of energy transfer path- 

 ways should Be made in terms of relative probabilities of energy 

 transfer to R^^ and R2 from a given light absorber. 



2) The cytochrome oxidation vs. intensity curve (Fig. 2) for 

 actinic wavelengths -vdiich activate both R, and R^ suggest that 

 the transfer ratio R-i/R2 ^^Y increase as the light inten- 

 sity is raised to very high levels. This implies that R2 ap- 

 proaches light saturation at lower intensities than R, . 



3) Cytochrome f (or -552) is oxidized by R-j^ via a mechanism 

 relatively insensitive to temperature, and is reduced by R2 and/ 

 or a short-circuit pathway around R, . Cytochrcane-552 oxidation 

 apparently requires 2 quanta per electron. Cytochrome reduction 

 has a temperature coefficient of about 2 per 10 degrees. 



k) Light-driven reduction of cytochrome b^ in Euglena chloro- 

 plast fragments and the interaction of added cytochrome -5 52 sup- 

 ports the proposal of Hill and B€ndall(9) that electron flow frcxn 

 R2 to R^ is mediated by cytochrome br and cytochrome f (or -552). 



5) The mechanism of 1,10 phenanthroline inhibition of the 

 Hill reaction and photosynthesis may be linked to the apparent 

 short-circuiting of R2 via cytochrome b^ in chloroplast frag- 

 ments. ^^*^^ 



REFERENCES AND NOTES 



B. Kok & G. Hoch, in Light and Life (W.D. McElroy & B. Glass, 

 eds.), Johns Hopkins Press, Baltimore, I96I, p. 39T« 



2 H.T. Witt, A. Muller, & B. Rumberg, Nature 192, 967, I96I. 



3 L.N.M. Duysens & J. Amesz, Biochim. Bio^Aiys. Acta 64, 2U3, I962. 

 ^ J. Amesz & L.N.M, Duysens, Biochim. BiojAiys. Acta ^, 26l, I962. 

 5 B. Kok & H. Beinert, Biochem. Bioi^ys. Res. Ccmmun . 9, 3^9,1962. 

 ° W.L. Butler, Arch. Biochem. Biophys . 93, 4l3, I96I. 



T J. Myers & C.S. French, J. Gen. Physiol . k3, 723, I96O. 



° M.B. Allen, L.R, Piette, & J.C. Murchio, Biochim. Biophys. Acta 



Q 60, 539, 1962. 



f R. Hill & F. Bendall, Nature I86, I36, I96O. 



Research carried out at Brookhaven National Laboratory under the 

 auspices of the U. S. Atonic Energy Commission. The coopera- 

 tion of Dr. John A. Bergeron in culturing the algae under con- 

 ditions of rapid autotrophic growth is appreciated. 



ID 



