VOL. 12 (1953) 



ENZYMIC OXIDATION OF |8-HYDR0XYBUTYRATE 



191 



precursor by a mechanism involving citrate formation, presumably the tricarboxyUc 

 acid cycle, but no oxidation of ^-BOH takes place in the absence of fumarate. 



The data in Table II also show that the Z-isomer gives rise to acetoacetate in the 

 presence of fumarate as well as in its absence, although in some experiments there is a 



TABLE II 



FORMATION OF ACETOACETATE AND CITRATE FROM d- AND /-/^-HYDROXYBUTYRATE BY INTACT 

 PARTICULATE PREPARATIONS OF LIVER AND KIDNEY 



All vessels in Experiments i, 2 and 3 contained 0.005 M MgClg, o.ooi M ATP, 0.014 M phosphate 

 buffer pH 7.5, 0.06 M KCl and liver particles from 0.45 g fresh liver in a total volume of 3.0 ml. In 

 Experiment 4 the vessels contained 0.005 M MgClj, o.ooi M ATP, 0.033 M phosphate buffer pH 7.5. 

 0.045 M KCl, and particles from 0.30 g fresh rat kidney, in 3.0 ml total volume. Where added, final 

 concentrations of /-BOH, f^-BOH and fumarate were o.oi M. Experiment i, 22°, 70 minutes; Experi- 

 ment 2, 25°, 60 minutes; Experiment 3, 25°, 44 minutes; Experiment 4, 30°, 70 minutes. 



Expt. 



Organ 



fi-Hydroxybutyrate 



Fumarate 

 added 



O2 uptake 

 microatoms 



Acetoacetate 

 formation 

 micromoles 



Citrate 

 formation 

 micromoles 



Liver 



Liver 



Liver 



Kidney 



significant decrease in acetoacetate formation in the presence of fumarate. Since previous 

 work with such enzyme preparations has indicated that acetoacetate is essentially inert 

 and accumulates quantitatively^^- ^^, formation of citrate from /-BOH would not be 

 expected if the /3-hydroxybutyric dehydrogenase represents the only mechanism of 

 oxidative attack on /-BOH. However, in many of our experiments (see especially Expt. 

 I, Table II) some extra citrate was actually formed from /-BOH although this extra 

 citrate formation from /-BOH never approached the amounts formed from rf-BOH. 

 The reasons for the rather unexpected formation of small amounts of citrate from /-BOH 

 under these particular conditions are not entirely clear but will be discussed later in this 



References p. 202. 



