of respiratory enzymes in tissues of dolphin and rat was made by DuBois 

 et al. (19U8), using homogenized liver, kidney, brain, skeletal muscle* 

 and cardiac muscle. Assays for cytochrome oxidase, succinic dehydrogenase, 

 and mal ic dehydrogenase demonstrated the presence of these enzymes in 

 dolphin tissues, although their activities were found to be lower than 

 were those in corresponding rat tissues. A slower rate of metabolism in 

 dolphin is indicated. 



Our knowledge of the tricarboxylic acid cycle in aquatic animals 

 is very incomplete. The presently available information can be summar- 

 ized in two figures. Figure 5 summarizes the known information on the 

 tricarboxylic acid cycle in teleosts and elasmobranchs. For the tele- 

 osts and elasmobranchs, identification of three important enzymes also 

 suggests that this cycle may be operative. In figure 6 is summarized our 

 present knowledge of the tricarboxylic acid cycle in oysters. For the 

 oyster, there is sufficient information in the form of the identification 

 of four of the important enzymes catalyzing the transformation of inter- 

 mediates of the tricarboxylic acid cycle to suggest that this cycle is 

 operative in these aquatic animals. In the oyster and in the large group, 

 teleosts and elasmobranchs, much more detailed knowledge is required be- 

 fore we will know if they have a tricarboxylic acid cycle that is the 

 same as that of land animals. 



ELECTRON TRANSPORT SYSTEMS, COENZYMES AND VITAMINS 



The aerobic transport of hydrogen and electrons to oxygen is accom- 

 plished by a chain of several carrier systems, beginning with dehydrogen- 

 ases, which act directly on their substrates, followed by flavoproteins, 

 and finally, the cytochromes. Some dehydrogenases are able to catalyze 

 the reaction of hydrogen removed from the substrate with molecular oxy- 

 gen. Other dehydrogenases, however, are linked to oxygen through the 

 cytochrome system. Many require pyridine nucleotides, such as DPN and 

 TPN, as coenzymes, and for others, the nature of the coenzyme is still 

 unknown. Also included in this chain are flavoproteins, some of whxch 

 are capable of dehydrogenating substrates directly, whereas others trans- 

 port electrons from pyridine nucleotides to the cytochrome system. These 

 en«ymes require the prosthetic group, flavin adenine dinucleotxde. 



The probability that the coenzymes of the hydrogen-transport system 

 are in fish is indicated by the results of numerous vitamin analyses of 

 fish tissues, since many of the vitamins have been found to be coenzymes 

 or precursors of coenzymes. Nicotinamide, which is incorporated in the 

 pyridine nucleotides, has been measured in various tissues of fish (itl- 

 gashi and Hirai 19U6 and Ghosh et al. 195D. Assays of commercially 

 important marine species for riboflavin, the precursor of £ la ™ ™ C ^?T 

 tides and flavin adenine dinucleotide, have been made by Sautier (19U6) 

 and by Higashi and Iseki (19U2 and 19U8). The distribution o .these B 

 vitamins in fish also has been reported by Umemura (1951 c , Stan grj£953), 

 Karrick (1955), Joshi et al. (1953), Braekkan et al. C 1 ?^), and ^raekkan 

 (1956). DPN and flavin have been determined in the eggs of Orlzias (Hi- 

 shida and Nakano 195U) and in the eggs of the sea urchin, Arbacia ^ahl 

 1950). 



17 



