II CARBOHYDRATES AND LIPIDS 889 



found that several transplanted tumors are capable of carrying on the condensa- 

 tion of acetyl coenzyme A with oxalacetate to form citrate at rates comparable 

 to normal tissues. From studies involving the incorporation of isotope from labeled 

 acetate, propionate, octanoate, pyruvate and glucose, Brown et al. (1956) con- 

 cluded that the citric cycle was operative in liver tumor. 



Several investigators have demonstrated that the succinoxidase activity is con- 

 siderably lower in malignant tissues than in the normal tissue of origin (Schneider 

 and Hogeboom, 1950; Dmochowski and Stickland, 1953; Mor, 1955). Schneider 

 and Potter (1943) reported that the succinoxidase activity of a group of rat tumors 

 ranged from 9-26 ml of oxygen consumed per mg dry weight per hour with 

 succinate as substrate. The values for normal tissues ranged from 18 for lung 

 to 219 for heart. These comparative values are quite representative of the relative 

 enzyme activities of normal and neoplastic tissues. Several investigators determined 

 the incorporation of radioactivity from acetate- i-^'*G into the succinate pools 

 induced by malonate in normal and neoplastic tissues in rats bearing Flexner- 

 Jobling carcinoma (Busch and Potter, 1952, 1952a, 1953; Busch, 1953; Busch 

 and Baltrush, 1954). A maximum incorporation into the succinate pool of normal 

 tissues occurred within 2-4 min. after the intraperitoneal injection of the labeled 

 acetate. The total radioactivity in the succinate pool accounted for 30% of the total 

 radioactivity within the kidney and approximately 10% in other normal tissues. In 

 the carcinoma, however, a high percentage of the radioactivity remained volatile 

 for 30 min/. after the injection of the acetate. This low incorporation of ^"^C into 

 the succinate pool within the tumor almost completely differentiates this tissue 

 from heart, spleen, lung and the other normal tissues. 



The anaerobic metabolism of pyruvate in homogenates of normal and neo- 

 plastic rat tissues has been investigated by Groth and LePage (1954). Under these 

 conditions, glycolyzing, homogenates of both normal tissue and Flexner-Jobling 

 carcinoma metabolized pyruvate at a rapid rate to yield components other than 

 lactic acid. One of the major products of the anaerobic metabolism was 1,2-pro- 

 panediol- 1 -phosphate in both tissues. In homogenates of the normal tissues the 

 decarboxylation of pyruvate to yield a two carbon fragment and CO2 was also 

 observed. Emmelot and Bosch (1955) studied the relative rates of pyruvate and 

 acetate incorporation into COj, amino acids, cholesterol and fatty acids in mouse 

 tumors in vitro. The ability of tumors to utilize pyruvate relative to acetate was 

 as follows : hepatomas, ovarian tumors of granulosa cell type and ovarian tumors 

 of the sarcomatoid type in increasing order. 



An important study on the metabolism of pyruvate in tumor bearing mice has 

 been made by Busch (1955). One mg of pyruvate-2-^'*C was injected into rats 

 with Flexner-Jobling carcinoma, Walker 256 carcinoma, or Jensen sarcoma. 

 The experiments were terminated from 15 sec. to 8 min. following the injec- 

 tion of the labeled pyruvate. In the normal tissues, 30-80% of the isotope was 

 converted into alanine, glutamic acid and aspartic acid within one min. after 

 injection of the radioactive compound. Adenine accounted for approximately 

 30% of the total isotope in liver, testes, muscle and intestine after injection of the 

 pyruvate. Tumors were slow to form labeled amino acids. At short time intervals 

 following the isotope administration a considerable quantity of ''^C was found 



Literature p. gic) 



