CAROTENOIDS 



S5mthesis, itself can be divided into two sub-phases. In the first sub- 

 phase (the first 3-5 days of growth) p-carotene synthesis is very slow 

 compared with general growth and lipid synthesis ; during the next 

 2-3 days, however, the rate of pigment formation is very rapid, this 

 coincides with the cessation of fungal growth. * ^ From 8-20 days the 

 amount of pigment present remains constant and thereafter it begins 

 to disappear until in a 36-day old culture, very little carotene remains. 

 This series of events is illustrated in Fig. 18. 



Effect of the Carbon Source. Variations in carbon source affect 

 carotenogenesis differently in different fungi. Glycerol, for example, 

 is the most effective single carbon source for pigment production in 

 Rhodotorula sanniei although a mixture of lactic acid and glucose is 

 equally effective. Glucose alone does not support pigmentation for, 

 in conjunction with gelatin as a nitrogen source, it will initiate but not 

 maintain pigmentation and a colourless yeast is produced. This form, 

 however, has not lost its ability to synthesize carotenoids for when 

 transferred to an adequate medium it assumes its original colour. * ^ 



Maltose and glucose are equally effective as carbon sources for 

 carotenogenesis in Phycomyces blakesleeanus, but xylose and fructose 

 are considerably less effective although equally good in promoting 

 general grovith and lipogenesis. Lactose was ineffective merely because 

 the fungus does not grow on a medium containing this carbohydrate as 

 its sole carbon source, i ». 2 o j^ the hands of Garton et al. ^ ° glycerol 

 was inactive for the same reason, but it should be noted that Schopfer** 

 found his strain of Phycomyces to grow reasonably well on glycerol. 



Schopfer and Grob ^ ^ have recently shown that Phycomyces grows 

 only slightly and produces no carotene when cultured on a medium 

 containing ammonium lactate as the sole carbon and nitrogen source. 

 If sodium acetate is added to this, medium growth is much improved 

 and some carotene is synthesized. This is taken to indicate that acetate 

 is a primary precursor of carotene. A direct demonstration of the 

 incorporation of acetate into the carotenoid molecule has been obtained 

 by Schopfer and his colleagues *®a using acetate labelled with C^* in 

 either the methyl or the carboxyl group. When the acetate was labelled 

 in the carboxyl group the activity of the carotene was twice that of the 

 carotene when the labelling was in the methyl group. 



Glover, Goodwin and Lijinsky*8B using 2-i*C-CH3COOH have 

 recently confirmed that acetate is utilized in the synthesis of carotene ; 

 they did not, however, obtain any evidence that the incorporation was 

 in any way specific. The original experiments of Grob, Poretti, von 

 Muralt and Schopfer**^ can also be interpreted in this way, for the 

 activity of the carotene should be higher when the methyl group 



110 



