STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 167 



this coenzyme to handle another molecule of DPH galactose. The iso- 

 merization of UDP-glucose appears to involve a cychc oxidation and reduc- 

 tion with enzyme-bound DPN as coenzyme (Maxwell, 1957). In addition to 

 UDP-coenzymes containing glucose and galactose, the following sugars have 

 also been observed bound via 1-glycosidic Imkage to UDP: iV-acetyl gluco- 

 samine, iV-acetyl galactosamine, glucuronic acid, galacturonic acid, D-xylose, 

 L-arabinose. The UDP-sugars have been shown to be the intermediates in 

 glycosyl transfer to form a large number of complex polysaccharides, such 

 as hyaluronic acid (Cifonelli and Dorfman, 1957) and chitin (Glaser and 

 Brown, 1957). In addition, UDP glucuronide is the coenzyme of glucuronide 

 formation m detoxication reactions. A similar coenzyme consisting of 

 guanosine diphosphomannose is involved in the transfer of this hexose. 



C. Phospholipid Synthesis 



The role of coA and the formation of acyl-ScoA derivatives have been 

 discussed earher (p. 83). The successive reaction of such acyl-coA derivatives 

 with a-glycerophosphate to form mono- and diesterified phosphatidates has 

 been presented in the discussion of Enzymatic Systems of Cytoplasm 

 (Section III, D, p. 84). These reactions may be summarized as shown in 

 formula (XXII). 



Fatty acids > acyl adenylates 



. coASH diacylphosphatidate 



^1 ATP acyl-ScoA acyl-ScoA 



a-glycerophosphate > monoacyl phosphatidate 



f DPNH 

 dihydroxyacetone phosphate 



(XXII) 



Mammalian tissues contam an enzyme which converts the phosphatidate to 

 an a-^-diglyceride. This may react with another acyl-ScoA to form a tri- 

 glyceride or with one of the forms of the cytiduie-containmg coenzymes to 

 form lecithins or cephahns, as described by Kennedy (1957) and Rossiter 

 et al. (1957). These reactions may be represented as shown in formula 

 (XXIII). 



cytidine triphosphate (CTP) -|- phosphoeholine ^ CPP-choline -\- PP 

 CTP -{- phosphoethanolamine ^ CPP-ethanolamine + PP 



