1852 SPECTROSCOPY AND FLUORESCENCE OF PIGMENTS CHAP. 37C 



spectra of "young" and "old" cultures of Rhodospirillum rubrum, the former ones con- 

 taining more rhodopin, the latter ones more spirilloxanthin (which is probably identical 

 with fhodoviolascin, cf. this chapter 37B, section 2(d) and is characterized bj^ a band at 

 550 mn). Whether all these differences are based on analogous changes in the assort- 

 ment of the carotenoids remains to be seen. 



Krasnovsky, Voynovskaya and Kosobutskaya (1952) suggested a new 

 interpretation also of the three infrared absorption bands of bacterio- 

 chlorophyll in vivo. As mentioned above, they attributed them to three 

 different states of aggregation of bacteriochlorophyll (rather than to three 

 different protein complexes, as suggested by Wassink and Katz, and 

 Duysens); they pointed out that at least two, and perhaps all three, of 

 these peaks can be observed also in colloids or solid films of chromato- 

 graphed pigment containing no proteins or other foreign molecules {cf. 

 section 3 above). 



This is not an implausible alternative to Wassink's interpretation, 

 since, apart from spectroscopic data, no other evidence for the existence of 

 three different bacteriochlorophyll-protein complexes in bacteria is pres- 

 ently available. More difficult to reconcile with experimental data is, 

 however, the additional hypothesis of Krasnovsky that the "aggregated" 

 forms of bacteriochlorophyll, ^vith absorption bands at 800, 850 and 890 

 m/x, which account for the bulk of the pigment in vivo, are "storage forms," 

 nonfluorescent and inactive, while the monomeric form, with a (hypo- 

 thetical) absorption peak at 780-790 van, is the only "active" one. 



Krasnovsky, Kosobutskaya and Voynovskaya (1953) noted a prefer- 

 ential bleaching and extraction of "Bchl 890" (compared to "Bchl 850" 

 and "Bchl 800"), and suggested that "Bchl 890" is the one of the three 

 "polymeric" forms most easily decomposed into the "monomeric" form. 

 However, they acknowledged that no absorption band of the "monomer" 

 could be observed in the expected location (780-790 m/z). To these 

 difficulties of Krasnovsky's hypothesis, one can add the physical im- 

 possibility of energy migration from the Bchl forms 890, 850 or 800, to 

 the hypothetical, active "Bchl 780"; and the experimental proof by 

 Duysens of energy migration in the opposite direction — towards Bchl 

 890. The fluorescence of the latter indicates that it serves as the final 

 energy acceptor, and probably also as the actual photocatalyst in bacterial 

 photosynthesis. We conclude that Krasnovsky's hypothesis is even less 

 plausible in the case of purple bacteria than we found it to be in that of 

 green plants. 



Krasnovsky and co-workers made some observations on the effect of 

 external factors on the three absorption peaks of colloidal dispersions of 

 bacteriochlorophyll-bearing material from purple bacteria, which origi- 



