050 ABSORPTION SPECTRA OF PIGMENTS IN VITRO CHAP. 21 



Absorption curves of colloidal chlorophyll-protein extract were given 

 also by Katz and Wassink (1939). Figure 21.29 shows the red band in the 

 spectra of Chlorella suspensions, and in colloidal extracts from the same 

 cells (a) in phosphate buffer pH 6.0, (6) in distilled water, (c) in Knop's 

 culture medium and (d) in fresh egg albumen. The position of the maxima 

 are but slightly different in all these ciu'ves (approximately 080 m/x); 

 the shapes of the curves are, however, affected by the nature of the medium, 

 particularly in extracts a and b. The solution in egg albumen has an ex- 

 tinction curve practically identical with that of the living cells. Fig. 21.29e 

 shows, as a contrast, the strong shift occurring upon extraction of the pig- 

 ment with alcohol. Similar curves were given by Katz and Wassink (1939) 

 and French (1940) for colloidal extracts from purple bacteria (c/. figs. 21.30). 



A transmission curve of a water extract of the blue-green alga Chroococ- 

 cus can be found in figure 22.48B. In these extracts, the phycocyanin- 

 protein forms a true colloidal solution, while the other pigments probably 

 are in the same state of dispersion as in extracts from green algae and leaves. 



C. Absorption Spectra of the Carotenoids* 



1 . Experimental Results 



The extinction curves of carotenoids in organic solvents have been in- 

 vestigated by numerous authors, among whom we may mention Willstatter 

 and Stoll (1913), Pummerer and Rebmann (1928), McNicholas (1931), 

 Smakula (1934), Gillam (1935), Sprecher von Bernegg, Heierle and Almasy 

 (1935), Miller (1935, 1937), Strain and co-workers (1938, 1942, 1943, 1944), 

 French (1941), Beadle, Zscheile and co-workers (1942, 1944, 1945) and 

 Zechmeister and co-workers (cf. review by Zechmeister 1944). 



Recently, a number of absorption curves were determined by Karrer 

 and co-workers, and were reproduced in a monograph by Karrer and Jucker 

 (1948). 



The absorption spectra of carotene and "leaf xanthophyll" in the in- 

 frared were observed by Stair and Coblentz (1933). They show a series 

 of absorption bands characteristic of long unsaturated carbon chains; 

 many of them coincide closely with the absorption bands of phytol (cf. 

 Table 21.IIA). 



The spectra of all carotenoids in the visible are characterized by two or 

 three intense bands near the violet end of the spectrum. Depending on 

 how far these bands extend into the blue and green, the color of the pig- 

 ments may be yellow, orange or even red. The position of the absorption 

 bands depends, often even more strongly than in the case of chlorophyll, 



* Bibliography, page 670. 



