Selective absorption of stereo-isomers of amino-acids from loops of the small intestine of the rat

Gibson, Quentin H.; Wiseman, G.

doi:10.1042/bj0480426

Cited by 134 publications

(38 citation statements)

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“…The results confirmed those of Gibson & Wiseman (1951) in showing that the L-enantiomorphs of both histidine and methionine were absorbed more rapidly than the corresponding D-enantiomorphs. As Since these results were obtained Hird & Sidhu (1957) have also shown by in vivo methods the inhibition of L-histidine absorption by L-methionine, and our results are a further confirmation of the inhibition of L-histidine by L-methionine shown by Wiseman in vitro.…”

Section: Proceedings Of the Physiologicalsupporting

confidence: 80%

Proceedings of the Physiological Society

1958

The Journal of Physiology

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Section: Proceedings Of the Physiologicalsupporting

confidence: 80%

Proceedings of the Physiological Society

1958

The Journal of Physiology

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“…The earliest studies in this area were conducted by Cori (19), who found that in the intact rat various sugars were absorbed at widely different rates, the order being galactose > glucose > fructose > mannose > xylose > arabinose. and histidine (23) in the small intestine. The evidence indicates that all these rapidly absorbed nutrients are taken up in the duodenum or proximal ileum, and direct measurements for some of these show that they seldom reach the distal end of the small intestine (22,24 are common in foods (25) but poorly absorbed, probably reaph the colon without attenuation in concentration.…”

Section: Absorption Patterns In the Intestinementioning

confidence: 99%

Genetic Regulatory Mechanisms and the Ecological Niche of Escherichia coli

Savageau

1974

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

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Whether the regulatory protein of an inducible operon for a catabolic pathway is a positive or a negative element in the control of expression is correlated with the frequent or infrequent presence, respectively, of the system's substrate in the natural environment.In several of the best-studied inducible operons of enteric bacteria, the regulatory protein acts as a negative (repressor) element in the control of gene expression. Examples are the galactose (1), glycerol (2), histidine utilization (3), and lactose (4) operons. In other well-studied inducible operons, like arabinose (5), maltose (6), and rhamnose (7), the regulatory protein is a positive (activator) element. These differences are represented schematically in Fig. 1. I will show that one can analyze the functional implications of these differences and predict that galactose, glycerol, histidine, and lactose are seldom in the organism's natural environment, whereas arabinose, maltose, and rhamnose are frequently present there. These predictions are confirmed by the absorption patterns for these substances in the mammalian intestine.The relative merits of genetic control by repressors and activators undoubtedly have been considered by many investigators. However, there have been no systematic attempts to compare these mechanisms on the basis of function and thus explore the reasons for their selection in nature. Clearly, the two types of mechanisms respond in opposite ways to mutations affecting (i) the synthesis of regulator, (ii) the degradation of regulator, and (iii) the mutual recognition of regulator and its binding site on the DNA. But there could be other functional differences, not necessarily intuitively obvious, responsible for the selection of these types of mechanisms. To examine this possibility one cannot compare directly two systems like the lactose and arabinose operons because of all their differences that are irrelevant to the comparison of the control mechanisms per se. Ideally, one would like a controlled comparison in which the two systems are identical in every respect except for the differences in the type of control mechanism utilized. Although this is difficult to do experimentally, it can be simulated by appropriate mathematical analysis. I have carried out such an analysis, which confirms the obvious behavioral differences mentioned above, but more importantly suggests that they are the only inherent differences between repressor and activator control (8). Therefore, it is these three kinds of mutations that must be examined further if we are to understand the natural selection of genetic control mechanisms. Natural mutational tendenciesOf the possible mutations affecting the synthesis and degradation of regulatory proteins, those that reduce the rate of synthesis and those that increase the rate of degradation presumably are the most common. It is reasonable to expect that only certain specific nucleotide sequences can result in a promoter with increased efficiency, whereas many different sequences could be promo...

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“…The transport system for D-amino acids across the intestinal membranes is the same as for L-amino acids but the L-amino acids have higher affinity (Gibson & Wiseman, 1951;Rosenhagen & Segal, 1974). D-Amino acids may be transformed to L-forms mainly in the kidney and liver (Man & Bada, 1987).…”

Section: Iii2 Absorption Distribution Excretionmentioning

confidence: 99%

Flavouring Group Evaluation 26: Amino acids from chemical group 34

2010

EFSA Journal

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The present Flavouring Group Evaluation deals with five amino acids.Three of the five flavouring substances possess one chiral centre and two possess two chiral centres.One of the substances is the naturally occurring L-amino acid, L-cystine .006], and another is the hydrochloride salt of a naturally occurring L-amino acid, 1-lysine monochlorhydrate ], for which the Panel concluded that the use of the Procedure was inappropriate, as the human exposures to L-cystine and L-lysine through food are orders of magnitude higher than the anticipated levels of exposure from the use as flavouring substances. Therefore, the flavouring substance L-cystine and l-lysine monochlorhydrate are not taken through the Procedure. However, the Panel concluded that the substances were not of safety concern at their estimated levels of intake as flavouring substances. The other three substances in this flavouring group are evaluated as racemates and are taken through the Procedure.The five flavouring substances are classified into structural class I.In its evaluation, the Scientific Panel as a default used the Maximised Survey-derived Daily Intakes (MSDIs) approach to estimate the per capita intakes of the flavouring substances in Europe. However, when the Scientific Panel examined the information provided by the European flavouring industry on the use levels in various foods, it appeared obvious that the MSDI approach in a number of cases would grossly underestimate the intake by regular consumers of products flavoured at the use level reported by the industry, especially in those cases where the annual production values were reported to be small. In consequence, the Scientific Panel had reservations about the data on use and use levels provided and the intake estimates obtained by the MSDI approach. In the absence of more precise information that would enable the Scientific Panel to make a more realistic estimate of the intakes of the flavouring substances, the Scientific Panel has decided also to perform an estimate of the daily intakes per person using a modified Theoretical Added Maximum Daily Intake (mTAMDI) approach based on the normal use levels reported by industry. In those cases where the mTAMDI approach indicated that the intake of a flavouring substance might exceed its corresponding threshold of concern, the Scientific Panel decided not to carry out a formal safety assessment using the Procedure. In these cases the Scientific Panel requires more precise data on use and use levels.According to the default MSDI approach, the five flavouring substances in this group have intakes in Europe from 0.12 to 30 microgram/capita/day which are below the threshold of concern value for structural class I (1800 microgram/person/day) substances.The human exposure of the candidate substance L-cystine .006] and l-Lysine from the candidate substance l-lysine monochlorhydrate .031] through food is orders of magnitude higher than the anticipated levels of exposure from the use of the flavouring substances. Therefore the two substances are not...

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Selective absorption of stereo-isomers of amino-acids from loops of the small intestine of the rat

Cited by 134 publications

References 5 publications

Proceedings of the Physiological Society

Proceedings of the Physiological Society

Genetic Regulatory Mechanisms and the Ecological Niche of Escherichia coli

Flavouring Group Evaluation 26: Amino acids from chemical group 34

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