CAROTENOIDS 



At the moment such a generahzed conception of the place of caro- 

 tenoids in the living world may seem very remote, but the wealth of 

 data, which has been presented in this book, must at some point be 

 holding out a master clue if only we had the wit to recognize and grasp 

 it. 



It has been thought that such a comprehensive theory may emerge 

 from a closer investigation of the relationship between carotenoids and 

 the reproductive processes, and the author recently fully reviewed 

 the evidence for this. ^ 



Eggs of a large number of animal species contain carotenoids, very 

 often xanthophylls. When xanthophylls are present in eggs they are 

 always unesterified and this, by analogy with vitamin A is a hint that 

 they are present in a functional form. Furthermore, egg carotenoids 

 are often present attached to proteins ; this recalls that in some sea- 

 urchins the pigment echinochrome when attached to protein may be 

 active in attracting spermatozoa. Body carotenoids can undergo changes 

 during the sexual cycle, for they are often mobilized into and meta- 

 bohzed by the gonads ; [^-carotene is actively metabolized during the 

 development of fertilized locust eggs. 



Sexual differentiation of carotenoid distribution is not confined to 

 the animal kingdom for we find fungi in which there is a marked 

 quantitative and often qualitative difi"erentiation of carotenoids between 

 the male and female gametes ; further, in the algae, participation in 

 sexual "processes has been noted with the crocetins which, if by the 

 definition adopted in this book, are not ** true " carotenoids, are 

 almost certainly derived from such compounds. 



Speculation can be pushed too far, but it may not have been inappro- 

 priate to conclude this monograph on a somewhat speculative note by 

 considering the territory open to conquest and possible lines of attack. 

 With the fundamental chemical data on the identification and dis- 

 tribution of the carotenoids so well founded and so considerable, the 

 time appears propitious for investigations aiming at the integration 

 of carotenoid biochemistry in a sound and comprehensive theory of 

 carotenoid metabolism. This demands an attack on a broad front with 

 the comparative approach as the spearhead. If such an attack is carried 

 out using all the weapons available to modern biochemistry then it is 

 possible that the next ten years will see advances sufficiently great to 

 allow wide generalizations concerning the biological role of the caro- 

 tenoids. 



REFERENCE 

 1. Goodwin, T. W. (1950), Biol. Rev., 25, 391. 



288 



