Amino acid free pool, table

Environmental salinity has been shown to alter rates of protein synthesis in fish tissues (Table 2). Studies have been carried out with both stenohaline and eu-ryhaline species protein synthesis rates of the former in response to salinity changes may represent stress responses, whereas in the latter species adaptive responses may be revealed. It is difficult to draw conclusions from the studies in Table 2, as amino acid-free pool-specific radioactivities were not published for any of the studies. 

All tissues contain free amino acids and a much larger fraction of bound (i.e. protein) amino acids. In cestodes, the free amino acid pool ranges from 100-400 mg/100 g fresh weight. Table 6.4 illustrates the qualitative differences that have been reported for the amino acids of some hymenolepidid cestodes (79). In general, however, there is no major departure in the amino acid content of cestodes from that of other organisms. 

DON can often be the largest pool of dissolved combined N but it is largely uncharacterized (see Chapter 3 by Aluwihare and Meador, this volume Bronk, 2002). The marine DON pool consists of highly reactive and relatively recalcitrant fractions and, while largely uncharacterized, includes a variety of compounds such as urea, dissolved free and combined amino acids and a variety of cellular intermediates, and excretion and degradation products that can be readily taken up (Table 7.1) and metabolized by phytoplankton and bacteria in the environment. Unfortunately, rates of DON uptake (excluding urea) are rarely measured. 

Some comments on the data are needed. Balance experiments show (Munro, 1972) that the average man of this size can be maintained in nitrogen equilibrium on an intake of 32 gm of high quality dietary protein. However, the customary protein intake in Western countries is about 90 gm daily. This is augmented by addition of some 70 gm of protein secreted into the gastro-intestinal tract (Table 1), so that the total load for adsorption is about 150 gm. Although this is a large amount, the pools of free amino acids in... 

The difference in nitrogen content is mainly due to the difference in protein content of the microorganisms. In fact, protein is the main cellular component containing nitrogen (in addition to RNA, DNA, free amino acids pool). The elemental composition of the main macromolecules is given in Table 11 protein contribute mainly to the N content, and RNA (5-15% cellular mass) and DNA (about 2% of cell mass) contribute to ash formation due to the phosphorus oxides. 

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