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Endogenous glycine and tyrosine production is maintained in adults consuming a marginal-protein diet

Endogenous glycine and tyrosine production is maintained in adults consuming a marginal-protein diet
Endogenous glycine and tyrosine production is maintained in adults consuming a marginal-protein diet
Background: The adequacy of indispensable amino acid supplies has received much attention in studies of protein requirements, but the availability of nitrogen for synthesis and maintenance of the supply of dispensable amino acids has been overlooked.

Objective: We aimed to determine whether nitrogen balance and the endogenous supply of the dispensable amino acids glycine and tyrosine can be maintained with a marginal protein intake.

Design: Phenylalanine, glycine, and tyrosine kinetics were measured in young adults (6 men, 6 women) on 4 occasions during a reduction in habitual protein intake (1.13 g·kg-1·d-1) to a marginal intake (0.75 g·kg-1·d-1) by using a multiple stable-isotope-infusion protocol.

Results: During the 10-d period of marginal protein intake, nitrogen excretion fell initially, then remained constant such that nitrogen balance was negative for the first 2 d and then positive or zero thereafter. Whole-body protein degradation and synthesis predicted from phenylalanine kinetics declined significantly (P < 0.05) over the period of marginal protein intake. Despite the reduction in the amount of glycine and tyrosine derived from whole-body proteolysis, the fluxes of glycine and tyrosine were maintained.

Conclusions: The results show that adaptation to a marginal intake of dietary protein consisted of an overall reduction in whole-body protein turnover, net protein catabolism, and the rate of nitrogen excretion. The conserved nitrogen was sufficient to maintain the endogenous synthesis and hence the supply of glycine and tyrosine.
phenylalanine, glycine, tyrosine kinetics, marginal protein intake, nitrogen balance, protein requirements, dispensable amino acids
0002-9165
511-518
Gibson, Neil R.
78736858-f72c-48e7-ae49-4a5519ffb3e4
Jahoor, Farook
7b3a0b55-f1a0-4dbd-bc48-d031a87a4ef0
Ware, Lisa
a56cf9e3-a3af-4df0-9b1f-4782aeda1384
Jackson, Alan A.
c9a12d7c-b4d6-4c92-820e-890a688379ef
Gibson, Neil R.
78736858-f72c-48e7-ae49-4a5519ffb3e4
Jahoor, Farook
7b3a0b55-f1a0-4dbd-bc48-d031a87a4ef0
Ware, Lisa
a56cf9e3-a3af-4df0-9b1f-4782aeda1384
Jackson, Alan A.
c9a12d7c-b4d6-4c92-820e-890a688379ef

Gibson, Neil R., Jahoor, Farook, Ware, Lisa and Jackson, Alan A. (2002) Endogenous glycine and tyrosine production is maintained in adults consuming a marginal-protein diet. American Journal of Clinical Nutrition, 75 (3), 511-518. (PMID:11864857)

Record type: Article

Abstract

Background: The adequacy of indispensable amino acid supplies has received much attention in studies of protein requirements, but the availability of nitrogen for synthesis and maintenance of the supply of dispensable amino acids has been overlooked.

Objective: We aimed to determine whether nitrogen balance and the endogenous supply of the dispensable amino acids glycine and tyrosine can be maintained with a marginal protein intake.

Design: Phenylalanine, glycine, and tyrosine kinetics were measured in young adults (6 men, 6 women) on 4 occasions during a reduction in habitual protein intake (1.13 g·kg-1·d-1) to a marginal intake (0.75 g·kg-1·d-1) by using a multiple stable-isotope-infusion protocol.

Results: During the 10-d period of marginal protein intake, nitrogen excretion fell initially, then remained constant such that nitrogen balance was negative for the first 2 d and then positive or zero thereafter. Whole-body protein degradation and synthesis predicted from phenylalanine kinetics declined significantly (P < 0.05) over the period of marginal protein intake. Despite the reduction in the amount of glycine and tyrosine derived from whole-body proteolysis, the fluxes of glycine and tyrosine were maintained.

Conclusions: The results show that adaptation to a marginal intake of dietary protein consisted of an overall reduction in whole-body protein turnover, net protein catabolism, and the rate of nitrogen excretion. The conserved nitrogen was sufficient to maintain the endogenous synthesis and hence the supply of glycine and tyrosine.

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More information

Published date: March 2002
Additional Information: Original research communication
Keywords: phenylalanine, glycine, tyrosine kinetics, marginal protein intake, nitrogen balance, protein requirements, dispensable amino acids

Identifiers

Local EPrints ID: 25533
URI: http://eprints.soton.ac.uk/id/eprint/25533
ISSN: 0002-9165
PURE UUID: c2c1d074-ef03-45cf-945c-109faa0ee00c

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Date deposited: 11 Apr 2006
Last modified: 15 Mar 2024 07:03

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Contributors

Author: Neil R. Gibson
Author: Farook Jahoor
Author: Lisa Ware
Author: Alan A. Jackson

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