Ammonotelic

Ammonia (NH3) is a relatively strong base, and at physiological pH values it is mainly present in the form of the ammonium ion NH4 (see p. 30). NH3 and NH4 are toxic, and at higher concentrations cause brain damage in particular. Ammonia therefore has to be effectively inactivated and excreted. This can be carried out in various ways. Aquatic animals can excrete NH4 directly. For example, fish excrete NH4 via the gills (ammonotelic animals). Terrestrial vertebrates, including humans, hardly excrete any NH3, and instead, most ammonia is converted into urea before excretion ureotelic animals). Birds and reptiles, by contrast, form uric acid, which is mainly excreted as a solid in order to save water uricotelic animals). 

Ammonotelic animals most aquatic vertebrates, such as bony fishes and the larvae of amphibia... 

Excess nitrogen is excreted as ammonia. Ammonotelic organisms excrete ammonia directly, uricotelic organisms excrete it as uric acid, and ureotelic organisms excrete it as urea. 

While the complete oxidations of fats and carbohydrates yield C02 + H20, the complete oxidation of amino acids yields C02 + H20 and as well as ammonia. Three fates of this so-called nitrogen waste product are common in animals it can be excreted into the outside medium (ammonotelism, which is common in many aquatic animals) it can be excreted as uric acid (uricotely, common in reptiles and birds) or, it can be excreted as urea (common... 

In humans and many other vertebrates, ammonia arising from deamination reactions or other sources is excreted in the form of urea. These animals are called ureo-telic. Fish excrete nitrogen in the form of ammonium ions and are therefore ammonotelic. Animals that need to conserve water excrete their nitrogen in the form of crystalline uric acid. They are uricotelic, or purinotelic. One often finds animals that convert uric acid to allantoin via uric acid oxidase (Figure 20.8). Allan-toin is more water soluble than uric acid. Uric acid oxidase is absent from primates. 

The endogenous repletion of water in the sea Lets nitrogenous excretion proceed quite easily For ammonia though toxic is quickly washed away So fish excrete (4 times) the ammonotelic way (repeat). 

Like the zooplankton (see Chapter 26 by Steinberg and Saba, this volume), marine teleost fish are primarily ammonotelic (Wood, 2001), but also can excrete a significant proportion of their TDN as urea or other DON compounds (in both early... 

Cohen, P.P. Biochemical aspects of metamorphosis Transition from ammonotelism to ureatelism. Harvey Lect. Series 60,119-154 (1964-1965)... 

The presence of urease in several ammonotelic invertebrates has been shown by many investigators. In these animals urea arises from the degradation of purines. 

The degradation of purines in ammonotelic animals and in some ureo-telic animals proceeds to ammonia and urea, respectively. The oxypurines, hypoxanthine and xanthine, are oxidized to uric acid which is in turn oxidized, under the influence of uricase, to allantoin. Hydrolysis of allantoin proceeds in two stages to yield allantoic acid, and finally urea and gly-oxylic acid. In ammonotelic animals urease cleaves the urea into carbon dioxide and ammonia. 

The end products of purine metabolism are uric acid in primates and uricotelic animals, allantoin in mammals other than primates, urea in the rest of the ureotelic animals, and ammonia in many of the ammonotelic animals. 

In terms of amino nitrogen excretion the animal kingdom can be classified into ammonotelic (ammonia), ureotelic (urea) and uricotelic (uric acid) organisms depending on the nature of the discharged substance. 

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