new protein is synthesized for growth and repair as also are essential 

 non-protein substances such as coenzymes, hormones, creatine, and choline 

 — to mention a few. Excess amino acids in this pool are deaminatedj 

 some, the glucogenic ami.no acids, are converted to glucose, while others, 

 the ketogenic amino acids, give rise to ketones. The end products of 

 many are yet unknown. Thus in addition to synthetic functions, amino 

 acids may serve as a source of energy. Hutchens et al. (1°U2) found that 

 certain samples of eggs of the sea urchin, Arbacia , consumed little or no 

 carbohydrate in early stages of development, during which cell division 

 proceeds most rapidly. Processes involving the oxidation of protein or 

 protein breakdown products could account for the observed uptake of oxy- 

 gen. Indeed, in some cases, ammonia production agreed with oxygen con- 

 sumed for complete oxidation of protein. Ammonia formed from the process 

 of deamination is eliminated either unchanged or in less toxic forms as 

 urea or uric acid* Protein metabolism, therefore, is essentially the 

 metabolism of amino acids and includes the pathways connecting their 

 interconversion and those leading to the synthesis of other nitrogenous 

 compounds, including nitrogenous waste products excreted by the animal. 



Detailed information of protein metabolism, as outlined above, is 

 al most nonexistent for fish, being limited almost completely to warm- 

 blooded animals and to microorganisms. By means of compositional studies, 

 however, possible relationships of amino acids to other metabolites found 

 in fish may be initially formulated, using information known for other 

 animals. Geiger (19U8) has reported the protein content of the muscle 

 of many species of fish and has compared the various fractions to mammal- 

 ian muscle. Included are proteins of fish blood, collagens, and proteins 

 isolated from fish sperm and from the female reproductive organs of fish. 

 Analyses of fish protein by many workers have shown over 20 of the common 

 amino acids to be present (Baertich and Weber 19U7, Geiger 19U8, Dunn et 

 al. 19U9, KakLmoto et al. 1953, Goncalves 1952, Master and Magar 195U, 

 Sugimura et al. 195U, and Eastoe 1957). Compared to beef muscle, fish 

 muscle has higher amount of glutamic acid (Jarpa 1950). The nature and 

 function of the red muscle of fish have been given much consideration. 

 Although it resembles heart muscle in certain respects, it has essen- 

 tially the same amino acid composition as has white muscle (Matsuura 

 et al. 1955). Studies of the extractive nitrogen of certain shellfish 

 and squid muscle have shown generally higher amounts of amino nitrogen 

 to be present than are found in vertebrate muscle (Simidu et al. 19!?3 

 and Endo et al. 19 5U). 



I^-amino acid oxidase, which catalyzes the oxidation of amino acids 

 to the corresponding a- keto acids and ammonia, occurs in marine inverte- 

 brates (Roche et al. 1952), Differing from the L-amino acid oxidase found 

 in many vertebrates, however, this enzyme in invertebrates is capable of 

 catalyzing the oxidation of basic amino acids, especially arginine Tissue 

 extracts of hepatopancreas and digestive tract of annelids, gephyriens, 

 mollusks, crustaceans, and echinoderms were able to oxidize Ir-histidine, 

 L-leucine, Ir-tryptophane, Ir- ornithine, and L-citrulline in aBTdition to 



2U 



