VOL. 4 (1950) 



ENZYMES FROM PIG HEART 



209 



lation) in the Jfirst 2 minutes per mg of protein, tested at 30^^*. Allowing for the difference 

 in temperature in the manometric tests of the two laboratories, it would appear that 

 the specific oxalosuccinic carboxylase activity of Lynen and Scherer's preparation 

 from horse liver was only about one fourth of that obtained by us starting with pig heart. 



INHIBITION OF OXALOSUCCINIC CARBOXYLASE BY ISOCITRIC ACID 



It has been reported that isocitric acid strongly inhibits the enzymatic decarboxy- 

 lation of oxalosuccinic acid as followed manometrically^. As shown in Fig. 2, this 

 inhibition can also be observed under the conditions of the optical test. The test system 



Fig. 2. Inhibition of oxalosuccinic carboxylase activity by isocitric acid; optical test. 



(Description in text). 



was as indicated in a previous section. Curves i and 2 were obtained with 0.02 and 0.04 

 ml respectively of the acetone powder extract of pig heart (about 0.12 and 0.24 mg of 

 protein). Oxalosuccinate (final concentration, 0.167- io~^ M) was added at zero time in all 

 cases. Curves 3 (-0-0-) and 4 {-A-A-) both with 0.04 ml of extract and either 0.35- io~^ 

 M (curve 3) or 0.35- ic"* (curve 4) fl',/-isocitrate. Curve 5 (-3-3-) with 0.02 ml of extract 

 and 0.35- io~^ M (^,^-isocitrate. 



A cknowledgement 



We are indebted to Mr Morton C. Schneider for technical assistance. 



SUMMARY 



Partial purification of the isocitric dehydrogenase and oxalosuccinic carboxylase activities of 

 pig heart has been obtained by means of ammonium sulphate and ethanol fractionation of an acetone 



* Manometric test with o.ooi M MnSO^ and 0.002 oxalosuccinate, pn 6.0. The purification proce- 

 dure involved water extraction of the fresh liver, precipitation with acetone, fractionation with 

 nucleic acid between pH 5-i8 and 4.6, and precipitation with ethanol. The average specific activity 

 of solutions of the acetone precipitate was 3.8. Yields were not reported and the fractions were not 

 tested for isocitric dehydrogenase. 



References p. 210. 



