104. PATHWAYS OF LIPID METABOLISM: MAMMALS (Concluded) 



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

 based on studies confined chiefly to mammals. 



blocked in diabetes mellitus, starvation (?). Insulin useful, probably necessary, but site of lipo- 

 genlc action not knovn -- possibly the hexokipase reaction in carbohydrate metabolism. /20/ Fatty 

 acid-CoA ester shortened 2 carbons at a time by p-oxidation, breaking off a molecule of acetyl ^^CoA 

 at each step, and re-esterifying the remainder with CoA. /21/ Acetic acid ester of coenzyme A 

 known also as S-acetyl coenzyme A, active acetyl. /22/ Via squalene7 /23/ Adrenal steroids (Cuoxy) 

 promote synthesis (?). /2l+/ Hormones, bile acids. /25/ Transported from liver via blood to other 

 tissues, where oxidized, via acetyl-^CoA and Krebs Cycle, to CO2 and HgO. Some conversion to ace- 

 tone. /26/ Coprosterol, epicoprosterol excreted. /27/ Tyrosine, leucine, isoleucine elLso converted 

 directly to acetoacetate . /28/ Aspartate enters Krebs Cycle not via pyruvate, but by conversion 

 directly to oxalacetate. /29/ Occurs in blood, liver, muscle, other tissues. /50/ Occurs in muscle, 

 especially in exercise, the lactate diffusing into the blood stream. /5l/ Occurs in liver, muscle, 

 brain, other tissues. /52/ ATP-dependent reaction with CoA. /53/ Diphosphothiamine (= cocarboxylase ) , 

 llpoic acid, Mg++ required, /j't-/ Pyruvate + COg — ^.oxalacetate, malate, components of Krebs Cycle. 

 Oxalacetate condenses with acetyl ^-' CoA, to form citrate. This removal of acetyL'>.'CoA by oxalacetate 

 (i. e.^ by pyruvate), occurring when acetyl'»--CoA is being formed in active fat catabolism, may ex- 

 plain antiketogenic action of carbohydrate 

 And energy liberation. 



(and protein). /55/ For Krebs Cycle see table 106. /56/ 



187 



