Protein Synthesis in Intestinal Mucosa: the Effect of Route of Administration of Precursor Amino Acids

Alpers, David H.

doi:10.1172/jci106788

Cited by 129 publications

(61 citation statements)

References 23 publications

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“…The precursor pool enrichment of leucine incorporated into the gastro-jejunal secretions was 1.6 ± 0.5 mpe. This confirms that plasma leucine is not the direct precursor pool of the intestinally secreted proteins, an assumption that has been previously formulated (Alpers, 1972). An underestimation of the isotopic enrichment of the precursor pool for luminally secreted proteins could originate from the reabsorption and possible subsequent transamination of labelled leucine in the intestine.…”

Section: Methodssupporting

confidence: 86%

Rate of [¹⁵N]leucine incorporation and determination of nitrogenous fractions from gastro-jejunal secretion in fasting humans

Gaudichon¹,

Laurent²,

Mahé³

et al. 1994

Reprod. Nutr. Dev.

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Section: Methodssupporting

confidence: 86%

Rate of [¹⁵N]leucine incorporation and determination of nitrogenous fractions from gastro-jejunal secretion in fasting humans

Gaudichon¹,

Laurent²,

Mahé³

et al. 1994

Reprod. Nutr. Dev.

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“…First, it is possible that only the upper villus cells, which are more likely to metabolize dietary amino acids, are capable of oxidizing lysine. This idea receives support from earlier studies of differences in the use of luminal and systemic amino acids for protein synthesis in different regions of the villus (18). Second, one could argue that the intracellular trafficking of amino acids depends strongly on whether amino acids enter the enterocyte across the apical or basolateral membrane.…”

Section: Discussionmentioning

confidence: 90%

“…Although both sources are used by the PDV (6,11,18), their relative contributions have received relatively little systematic study. The determination of the relative rates of arterial and dietary first-pass lysine metabolism in the PDV was the second objective of this study.…”

mentioning

confidence: 99%

Adaptive regulation of intestinal lysine metabolism

Goudoever

Stoll

Henry

et al. 2000

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

136

102

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The metabolism of dietary essential amino acids by the gut has a direct effect on their systemic availability and potentially limits growth. We demonstrate that, in neonatal pigs bearing portal and arterial catheters and fed a diet containing 23% protein [high protein (HP) diet], more than half the intake of essential amino acids is metabolized by the portal-drained viscera (PDV). Intraduodenal or i.v. infusions of [U-13 C]-lysine were used to measure the appearance across and the use of the tracer by the PDV. In HP-fed pigs, lysine use by the PDV was derived almost entirely from the arterial input. In these animals, the small amount of dietary lysine used in first pass was oxidized almost entirely. Even so, intestinal lysine oxidation (24 mol͞kg per h) accounted for one-third of whole-body lysine oxidation (77 mol͞kg per h). Total lysine use by the PDV was not affected by low protein (LP) feeding (HP, 213 mol͞kg per h; LP,186 mol͞kg per h). In LP-fed pigs, the use of lysine by the PDV accounted for more than 75% of its intake. In contrast to HP feeding, both dietary and arterial lysines were used by the PDV of LP-fed pigs in nearly equal amounts. Intestinal lysine oxidation was suppressed completely. We conclude that the PDV are key organs with respect to amino acid metabolism and that the intestines use a disproportionately large amount of the dietary supply of amino acids during protein restriction.T he portal-drained viscera (PDV; the intestines, pancreas, spleen, and stomach) contribute between 20% and 35% of whole-body energy expenditure and protein synthesis, even though they contribute less than 6% of body weight (1-3). Dietary amino acid use by the intestine could have a substantial effect on their systemic availability and thereby regulate wholebody protein deposition. Studies in a number of mammalian species show that dietary essential amino acids (EAA) are directly used by the intestines for protein synthesis and other biosynthetic pathways (4-6).Futhermore, under high protein (HP) feeding conditions, intestinal energy production is derived largely from the oxidation of glutamate, glutamine, and aspartate (7-9). However, the oxidation of these substrates accounts for neither the total CO 2 production nor the production of alanine and ammonia by the PDV. The failure to account for the nitrogen outflow from the metabolism of glutamate, glutamine, and aspartate has led us to conclude that other amino acids, possibly including EAA, are oxidized in the PDV. There is evidence that leucine and methionine are oxidized by the enterocytes (10, 11), but we know of no detailed in vivo investigations of intestinal catabolism of other EAA. In this context, the oxidation of lysine would be of particular consequence, because this amino acid is nutritionally first limiting in cereal-based diets and milk (12).Investigations carried out 25 years ago were unable to find evidence for the presence of enzymes required for lysine catabolism in enterocytes (13,14), and it is generally held that lysine catabolism occurs prima...

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“…Evidence of a degradatory pathway for newly synthesized microvillar enzymes has also been found in pig entcrocytes VilY) [23].…”

Section: Lyflw (!F C L L~~~r L ? R C ' T H~l R O T L~~mentioning

confidence: 84%

Biosynthesis of intestinal microvillar proteins. Expression of aminopeptidase N along the crypt-villus axis

Danielsen

1984

Eur J Biochem

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The expression of pig small‐intestinal aminopeptidase N (EC 3.4.11.2) along the crypt‐villus axis was studied in tangential sections of [35S]‐methionine‐labelled, organ‐cultured explants. The only detectable molecular forms of aminopeptidase N along the crypt‐villus axis were polypeptides of Mr 140000 and 166000, representing the enzyme in a transient and mature form respectively. The synthesis was at a very low level in the crypt region in experiments with labelling periods ranging from 10 min to 3 h. These findings indicate that crypt cells are not fully committed to the expression of aminopeptidase N, either in its mature or in any other immunoreactive molecular form. The expression of aminopeptidase N was markedly stimulated by dexamethasone (1 μg/ml). During labelling periods of 3 h, dexamethasone caused an approximately threefold increase in the expression of the enzyme in the crypt cells and a moderate increase of about 20% in the villus cells. Whereas the latter can possibly be ascribed to a general protective effect of dexamethasone on villus architecture, these experiments indicate that crypt cells of mucosa from adult individuals exhibit the same sensitivity to glucocorticoids as does the intestinal epithelium during the prenatal and early postnatal phase.

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Protein Synthesis in Intestinal Mucosa: the Effect of Route of Administration of Precursor Amino Acids

Cited by 129 publications

References 23 publications

Rate of [¹⁵N]leucine incorporation and determination of nitrogenous fractions from gastro-jejunal secretion in fasting humans

Rate of [¹⁵N]leucine incorporation and determination of nitrogenous fractions from gastro-jejunal secretion in fasting humans

Adaptive regulation of intestinal lysine metabolism

Biosynthesis of intestinal microvillar proteins. Expression of aminopeptidase N along the crypt-villus axis

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Protein Synthesis in Intestinal Mucosa: the Effect of Route of Administration of Precursor Amino Acids

Cited by 129 publications

References 23 publications

Rate of [15N]leucine incorporation and determination of nitrogenous fractions from gastro-jejunal secretion in fasting humans

Rate of [15N]leucine incorporation and determination of nitrogenous fractions from gastro-jejunal secretion in fasting humans

Adaptive regulation of intestinal lysine metabolism

Biosynthesis of intestinal microvillar proteins. Expression of aminopeptidase N along the crypt-villus axis

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Product

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Rate of [¹⁵N]leucine incorporation and determination of nitrogenous fractions from gastro-jejunal secretion in fasting humans

Rate of [¹⁵N]leucine incorporation and determination of nitrogenous fractions from gastro-jejunal secretion in fasting humans