96 



LIPIDES (fats and RELATED SUBSTANCES) 



thesized in the body from two-carbon fragments produced during carbo- 

 hydrate and fat metabolism. 



Ergosterol 



This sterol has acquired great importance because of the discovery 

 that it is the parent substance of one of the D vitamins. AVhen ergosterol 

 is exposed to ultra violet light for a few minutes, several new compounds 

 are formed. One of these, calciferol, has, besides chemical properties 

 that differentiate it from its parent substance, marked antirachitic 

 potency. (See discussion on vitamin D, p. 212, for details regarding 

 these changes.) 



Ergosterol is a white, crystalline compound, which has a melting point 

 of 160-161^0. It is obtained commercially from yeast and mold cells, 

 where it occurs in concentrations up to 2 per cent of the dry weight of 

 the fungal tissue. The dry yeast or mold is extracted with alcohol and 

 benzene, and on concentration of the extract, crystals of crude ergosterol 

 separate. Its chief commercial use is in the manufacture of vitamin D 

 preparations. 



BILE SALTS 



Bile aids in fat digestion (p. 317) because most of its solid matter con- 

 sists of bile salts, strong emulsifying agents which form water-soluble 

 complexes with fatty materials. These substances are sodium salts of 

 peptide-like combinations of glycine or taurine (NH2CH2CH2SO3H) with 

 bile acids, steroids bearing a carboxyl and one or more hydroxyl groups. 

 The commonest and most abundant bile acid is cholic acid, and the 

 glycine and taurine conjugates of it are glycocholic and taurocholic acids, 

 respectively. 



CH3 CH3 



HO H3CH(CH2)2COOH HO H3CH(CH2)2CONHCH..CH2S03Na 



HO' 



OH HO 

 Cholic acid 



Sodium salt of taurocholic acid 

 (a typical bile salt) 



PHOSPHOLIPIDES 



Phospholipides, or phosphatides, are fat-like substances that contain 

 phosphorus and nitrogen. Upon hydrolysis they are broken down into 



