succinic dehydrogenating ability of muscle tissue from carp and frog over 

 a temperature range of 10° to 30° C. The activity of the fish muscle was 

 constant within this range, whereas that of the frog muscle showed an 

 average Qiq of approximately 1.7. It appears that the two factors— a 

 relatively high oxygen consumption and a low temperature coefficient for 

 respiratory enzymes of fish, especially at low temperatures — are of value 

 in metabolic adaptation to temperature and also indicate an important 

 difference in these enzymes of fish compared to those of warm-blooded 

 animals. Such adaptation also has been noted by Steinbach (19U9) for ATP- 

 ase activity of cold- and warm-blooded animals. 



Of the enzymes of the TCA cycle involved in the uptake of oxygen 

 observed in these experiments, the succinoxidase system probably pre- 

 dominates, owing to its relative stability j however, numerous other enzym- 

 atic pathways account for some of this activity. Succinoxidase activity 

 has been observed in homogenized goldfish gill by noting the increase in 

 consumption of oxygen following the addition of succinate. Inhibition 

 studies with mercuric chloride showed this activity to be dependent upon 

 the presence of sulfhydryl groups (Sexton and Russel 1955). tJmeraura (1951 

 a,b, and c) investigated the respiratory enzymes of carp by comparing the 

 dehydrogenase activities of lateral red and white muscle, liver, and kidney 

 homogenates. Using the Thunberg technique and succinate or malate as 

 substrates, he found that red muscle showed five to eight times the activ- 

 ity of ordinary white muscle; the activities of liver and kidney were un- 

 affected by these substrates* Succinic and cytochrome oxidases also 

 demonstrated in these tissues were found to be most active in red muscle. 

 Thus the oxidative and reductive activity of the lateral red muscle of 

 fish far surpasses that of ordinary muscle and resembles that of heart 

 muscle in these respects. Measurements of succinic dehydrogenase and 

 cytochrome oxidase also have been made on a variety of homogenized tissues 

 of the toadfish (Lazarow and Cooperstein 1951) • Heart muscle was by far 

 the most active, followed by liver and kidney tissue. Compared with corres- 

 ponding preparations of rat tissues, approximately the same order of active 

 ity was shownj however, the absolute activity of rat heart was three times 

 that of toadfish heart. 



Homogenized eggs of the fish, Oryzias latipes, can oxidize several 

 substrates of the TCA-cycle (Hishida and itekano J.ySU) • The rate of up- 

 take of oxygen is stimulated by addition of citrate, succinate, malate, 

 glutamate, and pyruvate. ATP was found to have a stimulatory effect on 

 the oxidation of any of these substrates other than succinate. Qido- 

 genous oxygen uptake and succinoxidase activity increase as development 

 progresses* 



The citric acid content of fish muscle decreases after death and 

 is found to accumulate upon addition of pyruvic or oxalacetic acids (T*- 

 mada and Suzuki 1950) • As their work indicated, this is probably not 

 the result of microbial action but of the presence of the condensing 

 enzyme system. Yamada and Suzuki (1951) also reported a malonic acid 

 decomposing enzyme, present in carp-muscle homogenate, that decomposes 

 malonic acid into carbon dioxide and acetic acid. 



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