Protein and amino acid requirements

Young chicks also have a dietary requirement for proline (Baker, 1991), and this may also be required for collagen biosynthesis, since collagen is composed 

Amino Add Domestic fowl Quail White-crowned sparrow Maintenartce 

Source From Fisher (1972) Shim Vohra (1984) Murphy (1993a). 

Cysteine is also essential for normal growth, and this is probably because of the high proportions (ap- 

The essential requirement of histidine for growing chicks has been clear for some time, but whether or not it was required for the adult was less clear. It now seems justified to include it as one of the adult essential amino adds. Skeletal muscle, which comprises 30 to 40% of body protein, has considerable concentrations of the histidine-containing dipeptide camosine () -alanylhistidine). The metabolic function of camosine is not clear, although it has been suggested that it may be required as an antioxidant (Kohen et al, 1988) alternatively, it may act as an intracellular buffer, since the imidazole ring of histidine 

Calpains are enzymes that consist of a proteolytic subunit and a calcium binding subunit. In the cytosol, these enzymes are inactive due to binding of the inhibitory protein, calpastatin. Attachment to the cell membrane removes this inhibition and activation occurs at low concentrations of Csi ions. The enzymes hydrolyse proteins as far as peptides complete hydrolysis requires peptidases, which are also present in the cytosol. 

Very little is known of the mechanism(s) by which the rate of degradation is controlled. The current view is that the concentrations of ubiquitin, together with changes in the activity of the proteasome complex control the rate of proteolysis by this system. Lysosomal degradation may be controlled by the number of particles transported into the cell. The calpains might be controlled by the ion concentration. 

In Duchenne, the first symptom is muscle weakness in the early years of life which gradually worsens so that patients are unable to walk by the age of 10 years. Death from cardiac or respiratory insufficiency usually occurs before the age of 25. In Becker type, weakness and wasting becomes apparent between 5 and 25 years but, although severely disabled, patients can survive to a normal age. 

In 1987 the gene responsible for muscular dystrophy was identified, leading to the isolation of a protein, known as dystrophin, which is either totally absent in Duchenne, or partially absent in the Becker type. The protein is located on the inside of the plasma membrane of all muscles (and some neurones). Although its precise function is not known, the mutant form results in structural abnormalities of the plasma member which results in degradation of myofibrils, but the hnk between the abnormalities of the membrane and degradation is not known. One theory is that it leads to an increase in the activity of a Ca ion channel in the membrane and, therefore, a marked increase in the Ca ion concentration in the cytosol. This chronic elevation results in the activation of calpain, which leads to protein breakdown and the degeneration within the fibre (Chapter 13). 

Failure to control the rate of degradation of cyclins could lead to their over-expression, increasing the risk of tumour development. 

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Anthony A. Albanese, Protein and Amino Acid Requirements of Mammals, Academic Press, New York, N.Y., 1950. 

Benevenga, N. J., Gahl, M. J., Crenshaw, T. D., and Finke, M. D. (1994) Protein and amino acid requirements for maintenance and amino acid requirements for growth of laboratory rats. /. Nutr. 124, 451-453. 

WHO/FAO/UNU Expert Consultation (2007). Protein and Amino Acid Requirements in Human Nutrition. World Health Organization, Geneva Report of a Joint WHO/FAO/ UNU Expert Consultation. World Health Organization Technical Report No. 935. Winick, M. (1979). Hunger disease. Studies by the Jewish Physicians in the Warsaw Ghetto. John Wiley Sons, New York. 

Jensen, L.S. (1989). Relationship between protein and amino acid requirements of poultry. In Proc. Georgia Nutr. Conf, Atlanta Georgia, pp. 8-15. 

Elango R, BaU RO, Pencharz PB. Recent advances in determining protein and amino acid requirements in humans. Br J Nutr. 2012 108 Suppl 2 S22-30. 

University. Protein and amino acid requirements in human nutrition. Report of a joint FAOAVHO/UNU expert consultation (WHO Technical Report Series 935) 2007. 

The legitimacy of this approach has never been adequately tested. Although we cannot doubt that growth influences protein and amino acid requirements, the primary questions are whether the relative proportions of amino acids which are needed are similar for growth and maintenance. They probably are not. Secondly, what efficiency of utilization can one expect in the deposition of the body protein. 

Mlllward DJ (2001) Protein and amino acid requirements of adults current controversies. Canadian Journal of Applied Physiology 26 S130-S140. 

Table 3. Amino Acid Composition of Defatted Oilseed Meals and Amino Acid Requirements, mg/g Crude Protein...

HPLC Separation of Selenoamino Acids Selenium proteins and amino acids have a wide variety of ionic characteristics that are pH dependent [149, 151, 152] and can be separated by anion, cation, and re versed-phase chromatography [94, 97, 98, 133, 135, 152-157]. Maher and his coworkers [30, 32, 37] used both anion and cation HPLC to confirm the identity of Se species (Figs 20.1 and 20.3). It should be noted that selenocysteine is released from proteins complexes with cysteine and chromatographs differently than the commercially available selenocystine [158]. Although the major selenoamino acid in mullet has been tentatively identified as selenocysteine (Fig. 20.3), further confirmation is required. 

One of the first applications of HPLC in the clinical field was the quantitation of theophylline in asthmatic infants. This highly accurate measurement was an important test because of the very low amount of sample required and the accuracy of the determination (see Fig. 1-10). More recent clinically related HPLC separations include drugs and drug metabolites, neurochemicals and their metabolites, histamines, thyroid hormones, and enkephalins. The earliest bioresearch applications of HPLC included the determination of peptides, proteins, and amino acids. Application of HPLC to the analysis of these compounds remains important, as indicated by the rapid growth in references (Fig. 1-11). Bioresearch remains one of the most rapidly expanding growth areas of LC. 

The assembly of biological molecules, including proteins and nucleic acids, requires the generation of appropriate starting materials. We have already considered the assembly of carbohydrates in regard to the Calvin cycle and the pentose phosphate pathway (Chapter 20). The present chapter and the next two examine the assembly of the other important building blocks—namely, amino acids, nucleotides, and lipids. 

One significant difference between the LBT and the L-929 cytotoxicity test is the composition of the test median. The luminescent bacteria are suspended in a simple 2% sodium chloride solution, whereas the tissue culture cells require serum to supplemented their growth. Serum proteins and amino acids can complex with many chemicals, particularly metals, and thus rendo them unavailable to the test cells [27]. It was noted that for the 12 samples which were scored non-toxic with the LBT but positive to tissue culture, the Microtox F were <1.0 criteria established for a positive result. Depending upon the products or matoials under test, it may be practical and appropriate to use different F values as a failure point. These could correspond with the failure concentration established with the tissue culture or animal test for a specific class of material or product category. The highest sensitivity of the LBT should not be viewed as a cause of mme materials failing the test, but rather an q rtunity to set the failure point at a realistic and safe concentration. These correlations are discussed in depth by Jones [24]. 

Rama, P. B., Norton, H. W., and Johnson, C. (1964). The amino acid composition and nutritive value of proteins. V. Amino acid requirements as a pattern for protein evaluation. /. Nutr. 82, 88-92. 

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