CAROTENOIDS 



calorhodin. Heilbron, Lythgoe and Phipers^^*^ isolated crystalline ^- 

 carotenCy lutein (xanthophyll) and a new pigment myxoxanthin from 

 the fresh-water alga Rivularia nitida. This new carotenoid is not 

 specific to Rivularia nitida and was soon isolated from Rivularia atra 

 (marine) as well as from Oscillatoria rubescens (fresh water). ^ ' ^ Owing 

 to the large amounts of O. rubescens available this was examined in 

 detail and another pigment myxoxanthophyll was isolated. Reinvestiga- 

 tion of O. rubescens by Karrer and Rutschmann ^ ' ^ have confirmed 

 Heilbron and Lythgoe's observation and small amounts of an acidic 

 carotenoid oscillaxanthin and of zeaxanthin, which were not observed 

 by Heilbron and Lythgoe, were also isolated. The relation between 

 these pigments and those of Kylin has not yet been established. 



Tischer 1 ' 2, 1 7 3 isolated from Aphanizomenon flos-aquae four 

 carotenoids, aphanin, aphanicin, aphanizophyll and flavacin. Aphanin 

 and myxoxanthin are now known to be the same pigment and to be 

 identical with echinenone, ^'^'^ '^' first isolated from sea urchins by 

 Lederer ; ^ ' * this being so the name echinenone should be retained 

 and the others abandoned. For details of the properties of echinenone 

 see p. 163. 



Karrer and Rutschmann consider that myxoxanthophyll has the 

 following structure : 



OH Me 



but emphasize that this is by no means certain. The most obvious 

 objection to this structure is on spectroscopic grounds. It has a chromo- 

 phoric system of eleven congugated double bonds compared with twelve 

 in echinenone (or thirteen according to Karrer and Rutschmann), but 

 exhibits an absorption spectrum with its main band at a slightly higher 

 wavelength in ethanol (470 and 471 mjjL. respectively) and at a much 

 higher wavelength in chloroform (484 and 473 m(x. respectively) ; one 

 would have expected the bands to have maxima much lower than this. 

 Aphanizophyll is very similar to myxoxanthophyll, if not identical with 

 it ; Heilbron ^ ^ 6 considers their identity possible, but Tischer ^ ' ^ does 

 not agree. 



Aphanicin is thought to be a di-carotenoid, i.e., two aphanin (echine- 

 none) molecules joined by an ether bridge. Further work is required 

 before this suggestion can be fully accepted. Flavacin is, from its 



136 



