Newer concepts of the indispensable amino acids

Laidlaw, Stewart A.; Kopple, Joel D.

doi:10.1093/ajcn/46.4.593

Cited by 147 publications

(55 citation statements)

References 144 publications

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“…The most effective combination of dispensable N is glycine with either glutamic acid or an ammonium salt (Kies, 1972). Second, the classical perception of dispensability is too narrow (Jackson, 1983 ;Laidlaw & Kopple, 1987). The division between IAA and dispensable amino acids presumes that dispensability is conferred by the carbon skeleton (Rose, 1957).…”

Section: A M I N O a C I D D I S P E N S A B I L I T Ymentioning

confidence: 99%

“…On this basis, only lysine and threonine can be considered to be absolutely indispensable, and only alanine, glutamate and aspartate, which are formed by transamination from readily available intermediates, dispensable. All other dispensable amino acids are conditionally indispensable, being derived from IAA or exhibiting occasions in which the demand for them exceeds the capacity for their synthesis (Laidlaw & Kopple, 1987). Thus, leucine, isoleucine, valine, tryptophan, phenylalanine, methionine, threonine and lysine are indispensable ; glutamine, proline, histidine, arginine, tyrosine, taurine, glycine and serine are conditionally indispensable ; and glutamate, alanine and aspartate are dispensable.…”

Section: A M I N O a C I D D I S P E N S A B I L I T Ymentioning

confidence: 99%

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Human Amino Acid and Protein Requirements: Current Dilemmas and Uncertainties

et al. 1989

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Section: A M I N O a C I D D I S P E N S A B I L I T Ymentioning

confidence: 99%

Section: A M I N O a C I D D I S P E N S A B I L I T Ymentioning

confidence: 99%

Human Amino Acid and Protein Requirements: Current Dilemmas and Uncertainties

et al. 1989

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“…Although many aspects of amino acid metabolism are well understood, there are still important qualitative and quantitative issues to be studied. Such issues include the scale and regulation of the synthesis of an amino acid subgroup (exemplified by cysteine, glycine, proline, and arginine) that has been categorized as conditionally essential (12). The availability of uniformly 13C-labeled amino acid precursors would enable these questions to be studied experimentally.…”

mentioning

confidence: 99%

Uniformly 13C-labeled algal protein used to determine amino acid essentiality in vivo.

Berthold

Hachey

Reeds

et al. 1991

Proc. Natl. Acad. Sci. U.S.A.

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The edible alga Spirulina platensis was uniformly labeled with 13C by growth in an atmosphere of pure 3C02. The labeled biomass was then incorporated into the diet of a laying hen for 27 days. The isotopic enrichment of individual amino acids in egg white and yolk proteins, as well as in various tissues of the hen at the end of the feeding period, was analyzed by negative chemical ionization gas chromatography/mass spectrometry. The amino acids of successive eggs showed one of two exclusive enrichment patterns: complete preservation of the intact carbon skeleton or extensive degradation and resynthesis. The same observation was made in tissue proteins. These patterns were cleanly divided according to known nutritional amino acid essentiality/nonessentiality but revealed differences in labeling among the nonessential amino acids: most notable was that proline accretion was derived entirely from the diet. Feeding uniformly 13C-labeled algal protein and recovering and analyzing de novo-synthesized protein provides a useful method to examine amino acid metabolism and determine conditional amino acid essentially in vivo.The use of stable isotopically labeled amino acids has been the key to many developments in our understanding of the protein metabolism of humans (1-4). Stable isotopically labeled amino acids have also been used to examine some important practical questions concerned with human nutrition. In a recent series ofreports, Young and coworkers (5-7) have reported the use of amino acids labeled with 13C on the carboxyl group to examine the essential amino acid requirements of adult men; the studies have provided invaluable information about the obligatory metabolic "needs" for these amino acids (3,8). This approach, however, does not directly address questions related to the efficiency with which different dietary proteins support metabolic requirements. Such information is necessary if biological needs are to be converted into dietary recommendations. Questions about the extent to which dietary proteins support metabolic requirements can best be answered by comparing the use of dietary protein with free amino acids administered i.v. This method would enable an estimate of the significance of protein digestibility and absorptive processes for overall requirements of dietary amino acids.In general, 13C-, 2H-, and '5N-isotopes are inserted into single amino acids via specific chemical reactions. This process limits the number of positions within a given molecule that can be labeled, which, in turn, limits the metabolic information that can be obtained from studies with commercially available amino acids.Apart from the extremely high sensitivity with which uniformly labeled substrates can be detected, they can be used to great benefit in studies of intermediary metabolism. For example, several recent reports describing hepatic glucose metabolism in vivo have depended on the use of [U-_3Clglucose (9-11) and have included a detailed analysis of the mass isotopomer labeling patterns in the circulating glu...

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“…The classical perception of essential (indispensable) and nonessential (dispensable) amino acids was based on the presumption that essentiality was a feature conferred by the structure of the carbon skeleton (Rose, 1957). This perception is too narrow (Jackson, 1983;Laidlaw & Kopple, 1987). With the use of 15N labels it is possible to demonstrate that there is specific channelling of amino groups between amino acids (Jackson & Golden, 1980;Jahoor er al.…”

Section: Vol 48mentioning

confidence: 99%

“…pyruvate, a-ketoglutarate or oxaloacetate, which can be readily aminated in transamination reactions. All the other non-essential amino acids can be shown to be conditionally essential, and are potentially formed from essential amino acids (Table 2) (Laidlaw & Kopple, 1987).…”

Section: Vol 48mentioning

confidence: 99%

Optimizing amino acid and protein supply and utilization in the newborn

Jackson

1989

Proc. Nutr. Soc.

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As has been pointed out already (Casey, 1989) homologous milk appears to promote optimal growth and well-being in the infant, although it is not .entirely clear why this should necessarily be so. The difficulty in fully understanding the basis of the relations is particularly well illustrated for protein and amino acids. Within the framework of our general appreciation of nitrogen and protein requirements (Food and Agriculture OrganizatiodWorld Health Organizatioflnited Nations University, 1985), the N content of human milk is remarkably low, whether expressed in relation to the total energy content, or the amount ingested daily by the infant. It would appear that all the protein in the milk is not digested and absorbed. This may be particularly true for certain classes of proteins such as immunoglobulins, although we do not have any precise, quantitative information on the extent of this malabsorption. On the other hand, about 25% of the N in human milk is not present as protein at all. A portion can be identified as free amino acids, but by far the largest contribution, about 60%, comes from urea-N (Harzer et af. 1984). The urea-N has generally been considered to be metabolically unavailable. If this is so, the available protein would appear to be exceptionally low at a time when the demands for infant growth, development and elaboration are at their highest (Fomon & Macy, 1958). With our present concepts of protein and amino acid metabolism it is not possible to rationalize the apparent contradiction between the N requirements for growth and that available from breast milk. In order to make sense of the observed reality, we have to be prepared to consider alternative frameworks of understanding.In order to usefully approach this problem I have to start from a base of assumptions founded on experimental observations. There are four propositions I think it necessary to accept in order to be able to proceed.

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Newer concepts of the indispensable amino acids

Cited by 147 publications

References 144 publications

Human Amino Acid and Protein Requirements: Current Dilemmas and Uncertainties

Human Amino Acid and Protein Requirements: Current Dilemmas and Uncertainties

Uniformly 13C-labeled algal protein used to determine amino acid essentiality in vivo.

Optimizing amino acid and protein supply and utilization in the newborn

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