3 FUNCTION IN TNE ANIMAL ORGANISM n 



the opinion that they are more Hkely to function as protectors for sensitive 

 enzymes in the cell. Warburg and Negelein^ considered that carotene and 

 xanthophyll are photochemically active in assimilation. Fodor and Schoen- 

 FELD^ have recently reported that colloidal carotene solutions can act as hydro- 

 gen acceptors, and consider the possibility that they fulfil a similar function 

 in the respiratory process. 



It has also been suggested^ that certain carotenoids (e.g. y-carotene) play a 

 part in the reproduction of algae. There appears to be no certain foundation 

 for this hypothethis. Some investigators^^ assume that carotenoids influence 

 the growth of plants, and Buexxixg^^ has recently attempted to identify the 

 pigment concerned in the phototropy of plants with ^-carotene. 



According to Kuhx, Moewus and Jerchel^-, crocin (crocetin digentiobiose 

 ester), as well as cis- and /raws-crocetin dimethyl ester play a part in the re- 

 production of the unicellular algae chlamydomonas eugamctos f. simplex. It 

 appears that crocin can induce the formation of flagella in the gametes, while 

 mixtures of trans- and c/s-crocetin methyl ester convert the motile, but still 

 infertile gametes into male and female gametes. The ratio of cis- to trans- 

 crocetin methyl ester determines whether male or female gametes are formed. 

 These experiments require further confirmation. 



As the result of recent investigations (cf. p. 66) which show that various 

 carotenoid epoxides are widely distributed in plants, it has been suggested that 

 these compounds play a part in the transport of oxygen or in oxidation re- 

 actions^^. 



All these investigations are still at a preliminary stage and further researches 

 will be required in order to elucidate the importance of carotenoids in plants. 



3. THE FUNCTION OF CAROTENOIDS IN THE ANIMAL ORGANISM 



We are somewhat better informed regarding the significance of certain 

 carotenoids in the animal organism, but again many important problems still 

 require to be elucidated. A number of carotenoids are converted into vitamin A 

 in the animal organism and therefore play the part of pro-vitamins. Further- 

 more, carotenoids play a part in the visual process, but their function is as yet 

 incompletely understood. 



a. Carotenoids as Pro-vitamins A 



• 



Numerous papers have been published dealing with the function of carote- 

 noids as pro-vitamins A^*. Only a brief summary of the definitely established 

 facts will be given here. For further details, the original literature should be 

 consulted. 

 References p. ly—ig. 



