BACTERIOCHLOROPHYLL AND BACTERTOVIRIDIN 1787 



formed during the extraction, can be separated from the bulk of the blue 

 pigment by chromatography; after bacteriochlorophyll has been so puri- 

 fied it proves (luite stable, not only in crystalline form (c/. section 5 above), 

 but also in ethereal solution. 



The green oxidation product, obtained in the preparation of bacterio- 

 chlorophyll, probably has the oxidation level of dihydroporphin, and may be 

 identical with the green compound obtained by Schneider (c/. p. 445) by 

 oxidation of bacteriochlorophyll with ferric salts, iodine, quinone and other 

 mild oxidants, and by Krasnovsky and Voynovskaya (1951) by the action 

 of quinone on a bacteriochlorophyll solution in toluene. The latter ob- 

 servers reported that the oxidation can be reversed by ascorbic acid— an 

 interesting suggestion which needs confirmation. The oxidation product 

 has a chlorophyll-type spectrum, with the main absorption bands at 432 

 and 677 mu (as measured by Holt and Jacobs in ether) ; it fluoresces with. 

 red hght. Fischer (p. 445) suggested that it may differ from bacterio- 

 chlorophyll only by the absence of two H atoms in ring II, and also that 

 the "bacterioviridin" of green sulfur bacteria may be identical with it. 



Seybold and Hirsch (1954) reported that the azure-blue, non-fluorescent (more 

 correctly: infrared fluorescent!) bacteriochlorophyll (which they called "bacteriochloro- 

 phyll a") is, in vitro, "extraordinarily unstable," and is converted "in a few minutes" 

 into a green "bacteriochlorophyll b" (obviously the above-mentioned green oxidation 

 product!). 



The question of the chemical identity of hacteriovindin remains to be 

 settled. Barer and Butt (1954) found, in pigment extract from green bac- 

 teria, two main absorption bands, at 664 and 434 m^, respectively. The 

 first one is markedly different from the red band of the oxidation product of 

 bacteriochlorophyll (677 m/x) ; both bands are almost coincident with the 

 peaks of chlorophyll a. Barer asked whether ''bacterioviridin" could not 

 be identical with chlorophyll a; but noted differences in the position of 

 the minor bands and in the chromatographic behavior, which argued against 

 this identity (cf. also Katz and Wassink's curves in Fig. 21.7!). 



Seybold and Hirsch's absorption curve of an extract from Microchloris showed three 

 peaks, including, in addition to Barer's "red" and "violet" peaks, also a peak in the far 

 red, at 770 m/x, just where the bacteriochlorophyll band is usually found. Seybold and 

 Hirsch interpreted this as evidence that green bacteria contain, in vivo, the same "bac- 

 teriochlorophyll a" as the purple ones, but that this pigment is rapidly converted (oxi- 

 dized) into "bacteriochlorophyll 6" ( = bacterioviridin) upon extraction. An alternative 

 explanation is, however, that Sej'bold and Hirsch's culture of Microchloris, when used 

 for pigment extraction, was contaminated with purple bacteria. (The absorption curve 

 given by them for live Microchloris cells shows a weak but unmistakable band at 850 m^, 

 typical of purple bacteria ! ) 



We will see in Chapter 37C (section 6c) that the absorption spectra of live green 

 (and purple) bacteria, given by Seybold and Hirsch, also disagree with those found by 



