TRIGLYCERIDES AND FATTY ACIDS 107 



actively reduced by butyryl-CoA, altliough the aoti^'it.y was enhanced by 

 the presence of the Cu ion. 



(b') Unsatui'ated Fatty Acyl-Coenzyme A Hydrase. — Wakil and Mah- 

 Ipj.164 ^ygi-g the first to isolate and to purify a hydrating enzyme from beef 

 liver mitochondria wliich had a specific action on unsaturated acyl deriva- 

 tives of CoA. The preparation was shown to catalyze the hydration of 

 a,^-, and also of /3,7-unsaturated acyl-CoA derivatives. The enzj^me is. 

 specific for the trans isomer; at equihbrium, the ratio of /3-hydroxy to total 

 unsaturated acyl-CoA derivative equals 1.4 ± 0.2. The hydrase is acti- 

 vated with reduced glutathione (GSH) and cysteine; it is inhibited by p- 

 chloromercuribenzoate, iodoacetamide, and iodosobenzoate. 



(c') /3-Hydroxyacyl-Coenzyme A Dehydrogenase. — Wakil and collabo- 

 rators'®" likewise isolated and partially purified a second enzyme from 

 beef liver mitochondria which catalyzes the oxidation of ^S-hydroxyacyl- 

 CoA derivatives in the presence of diphosphopyridine nucleotide (DPN), 

 which serves as an electron acceptor. The enzyme was found to act on all 

 ^-hydroxyacyl-CoA derivati^'es from C4 to C12; it was optically specific for 

 the product of the imsaturated acyl-CoA hydrase. i.e., c?-/3-hydroxyacyl- 

 CoA. The optimal pH was found to be 10.0. At this pH the reaction pro- 

 ceded completely from left to right, while at a low^r value the equilibrium 

 could be shifted in favor of the /3-keto-acyl-CoA formation by the use of the 

 Mg ion as a complexing agent. 



b'. Fatty Acid Oxidases: These enz3'mes catalyze the oxidation of acyl- 

 CoA to i3-ketoacyl-CoA, with DPN as the primary external electron ac- 

 ceptor.'®' Beinert'®® was able to prepare acetoacetyl-CoA (CH3-CO-CH2- 

 CO-CoA), ;S-ketohexanoyl-CoA (CHs-CHa-CHa-CO-CH-rCO-CoA), and (3- 

 ketooctanoyl-CoA (CH3-(CH2)4-CO-CH2-CO-CoA) by enzymatic de- 

 hydrogenation of the corresponding (8-h3'droxy deri\'atives of CoA. The 

 compounds were identified by determination of the nature of the /3-keto 

 acid after alkaline hydrolysis, by enzymatic reactions, and by their spectral 

 properties. The compomids were found to be of the same order of sta- 

 bility as other knowii acyl derivatives of CoA. They were readily sus- 

 ceptible to enzymatic cleavage in the presence of reduced CoA. 



According to Wakil and Mahler,'®'' the sparking or activation ol fatty 

 acids and their oxidized derivatives before oxidation by fatty acid oxidase 

 systems involves the formation of S-acylated CoA derivatives. 



e\ Cleavage Enzymes: These Ijring about the change of /3-ketoacyl- 

 CoA to acetyl-CoA and acyl-CoA. The latter product contains two less 

 carbons than does its parent keto compound.'®' Goldman'®* recently re- 

 ported the fifteen-fold purification of the cleavage enzyme (CE) obtained 



