104. PATHWAYS OF LIPID METABOLISM: MAMMALS 



These pathways are believed to occur in the lipid metabolism of animal forms in general. They are 

 based on studies confined chiefly to mammals . 



Triglycer- 

 ides!. 2. 3?. 4 



Di- and Mono- 

 glycerides3'4.6 



Phospho- 

 lipid!. 2. 3, 4, 13 



a-.p ?-Glycero- 

 phosphoryl-cho- 

 line!4; Glycero- 

 phosphate 



Protein! -5 



Ketogenic 

 Amino Acids! 



Glycogenic 

 Amino Acids! 



Carbohy- 

 drate! • ^ 



Acetate29 



■52- 



Pyruvate29 



3!V 



.53' 



Lactate 



/l/ In intestinal lumen, blood, liver, other tissues. /2/ In chyle. /5/ Some absorption by intes- 

 tinal mucosa, /hf Formed in intestinail mucosa, or absorbed from lumen, pass into chyle, short chains 

 possibly also into portal blood. /5/ Digestion in intestinal lumen. /6/ Probably transitory in 

 tissues. /?/ In intestinal mucosa, liver, other tissues. /8/ Occur free (ionized) in intestinal 

 lumen, blood, liver; free existence in chyle, questioned; free existence probably transitory in 

 other tissues, if it occurs. /9/ In liver, carbon chains lengthened or shortened (cf. Fn 20), and 

 H added to C9.10, or removed creating double bonds. /lO/ Chiefly (?) unsaturated, /ll/ Synthesis 

 probably in intestinal mucosa, liver, blood. /12/ In chyle, blood, and small amounts in liver, 

 other tissues; not in brain, red cells. /15/ Chiefly lecithin, cephalins (phosphatides of ethanol- 

 amlne, serine, inositol, acetal, and polyglycerlde phosphatides) some sphingomyelin, /ll^/ln intes- 

 tinal mucosa, liver (7), other tissues (?). Split to choline, glycerol, phosphoric acid. /15/ In 

 Intestinal lumen, absorbed by intestinal mucosa, where resynthesized Into glycerides. Including 

 phospholipids. Metabolized to pyruvate. /16/ In liver, other tissues. /I?/ Fatty acid ester of 

 coenzyme A, 1. e., acyl/>^'CoA ester, formed by ATP-dependent acylatlon of CoA or by transfer of CoA 

 from succlnyl- or other CoA ester. /18/ Coenzyme A probably = pantetheine (pantothenic acid + 

 p-alanlne + thloethanolamlne) + ADP, with a third PO4 at C5 of the rlbose; forms fatty acid thiol 

 esters via the SH in the thloethanolamlne. /19/ Reverse of p-oxidatlon (cf. Fn 20). Retarded or 



186 



