The activation of intestinal brush border sucrase by alkali metal ions: An allosteric mechanism similar to that for the Na+-activation of nonelectrolyte transport systems in intestine

Mahmood, Akhtar; Alvarado, Francisco

doi:10.1016/0003-9861(75)90290-8

Cited by 25 publications

(5 citation statements)

References 9 publications

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“…Sucrase activity was assayed by measuring the liberation of glucose from sucrose as described by Mahmood & Alvarado (1975).…”

Section: Cell Isolationmentioning

confidence: 99%

A rabbit jejunal isolated enterocyte preparation suitable for transport studies.

Brown¹,

Sepúlveda²

1985

The Journal of Physiology

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SUMMARY1. A method is described for isolating viable enterocytes from rabbit jejunum. Estimates of sucrase and y-glutamyl transferase activities in cells isolated by this method suggest that they originate from the upper villus only.2. Isolated cells accumulate both oc-methyl-D-glucoside and alanine, maintaining high intracellular concentrations for at least 60 and 40 min respectively. Accumulation of a-methyl-D-glucoside is inhibited by the presence of phloridzin.3. The cells accumulate 42K and 86Rb in an identical manner. This uptake, which is maintained for at least 60 min, is inhibited in the presence of ouabain. Passive efflux of 42K and 86Rb occurs with rate constants which are virtually identical. The efflux follows a single exponential suggesting that it originates from only one intracellular compartment.4. It is suggested that the preparation can be used to study the effect of sugars and amino acids on K efflux. The advantages of using such a preparation are discussed.

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“…Sucrase activity was assayed by measuring the liberation of glucose from sucrose as described by Mahmood & Alvarado (1975).…”

Section: Cell Isolationmentioning

confidence: 99%

A rabbit jejunal isolated enterocyte preparation suitable for transport studies.

Brown¹,

Sepúlveda²

1985

The Journal of Physiology

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“…The absorption of amino acids and leucine aminopeptidase activity were re duced in the intestine of scorbutic animals. A functional relationship similar to one pro posed for disaccharidases and the sugar trans port system [19,26] has already been de scribed between the amino acid transport sys tems and peptidase activity in the intestine [22], The results indicate that various trans port systems and enzyme activities in intes tine are differently affected in scurvy, pre sumably because of discrete metabolic mech anisms responsible for these functions.…”

Section: Discussionmentioning

confidence: 87%

“…A functional link between sucrase-and carrier-mediated sugar transport system in the intestine has been demon strated [19,26]. Since both sucrase and the process of sugar uptake are stimulated in scurvy, this would provide indirect evidence for the functional association between these two systems.…”

Section: Discussionmentioning

confidence: 99%

“…The supernatant was removed and used for the assay of various en zymes. Brush border sucrase and maltase were assayed as described previously [19]. Alkaline phosphatase was determined according to the method of Bergmeyer [8], The Leucine aminopeptidase activity was esti mated by the method of Goldbarg and Rutenberg [13].…”

Section: Measurement O F Intestinal Uptakementioning

confidence: 99%

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Effect of Vitamin C Deficiency in Guinea Pigs on Intestinal Functions and Chemical Composition of Brush Border Membrane

et al. 1981

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The effect of vitamin C deficiency on the digestive and absorptive functions of the gut has been investigated in guinea pigs. The absorption of D-glucose was significantly elevated, but that of L-leucine, L-alanine and L-lysine considerably depressed in the intestine of scorbutic guinea pigs compared to controls. The intestinal transport of vitamin B₁₂ was also diminished. Activities of sucrase and alkaline phosphatase on the brush border were enhanced, but that of leucine aminopeptidase markedly reduced in scorbutic animals compared to controls. Maltase activity was unaffected in vitamin C deficient animals. Chemical analysis of the brush borders isolated from scorbutic animals revealed a considerable decrease in membrane protein, total lipids, phospholipids, and free cholesterol contents compared to control animals. In vivo 2-¹⁴C-acetate incorporation into membrane lipids suggested that the observed decrease in lipid components of the scorbutic membranes is due to reduced synthesis. Administration of ascorbic acid to scorbutic animals ameliorated the intestinal aberrations observed in scurvy.

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“…We base our reasoning on the general kinetic model originally proposed by Alvarado (1966,1967,1971), which considers the reciprocal, allosteric, interactions between two distinct binding sites: one for the substrate, S, and another for the allosteric modifier, A, which can behave either as an activator or as an inhibitor ( Fig. 1 in Mahmood, 1974, andAlvarado, 1978 is also applicable to cases such as the non-obligatory activation of an enzyme by a metal ion (Mahmood & Alvarado, 1975). In the special case of membrane transport, both S and A can be considered as substrates for their own respective carriers or, more precisely, binding sites.…”

Section: Theoretical Considerationsmentioning

confidence: 99%

A kinetic study of the interactions between amino acids and monosaccharides at the intestinal brush‐border membrane.

Alvarado¹,

Robinson²

1979

The Journal of Physiology

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SUMMARY1. The influx of amino acids into guinea-pig intestinal rings in vitro is inhibited by monosaccharides, and that of monosaccharides by amino acids. Two hypotheses have been proposed to account for these heterologous interactions. According to the first, the cis hypothesis, there is an allosteric interaction between substrates binding to separate but related sites at the outer face of the brush-border membrane matrix. In contrast, the trans hypothesis envisages the interaction to result from a partial dissipation of the electrochemical sodium gradient due to the cotransport of each substrate with sodium ions.2. In an attempt to distinguish between the merits of the two hypotheses, we examined the kinetics of the inhibition of phenylalanine influx by two sugars of widely different affinities, galactose and fl-methylglucoside. Since fi-methylglucoside carries more sodium into the cell than galactose, the trans hypothesis would predict it to be the stronger inhibitor, but in fact the opposite result is found.3. Equations were developed to describe the inhibitions in accordance with the cis hypothesis. The satisfactory agreement between experimental observations and theoretical predictions provides support for the applicability of the model. Further implications of the polyfunctional carrier model are discussed.

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The activation of intestinal brush border sucrase by alkali metal ions: An allosteric mechanism similar to that for the Na+-activation of nonelectrolyte transport systems in intestine

Cited by 25 publications

References 9 publications

A rabbit jejunal isolated enterocyte preparation suitable for transport studies.

A rabbit jejunal isolated enterocyte preparation suitable for transport studies.

Effect of Vitamin C Deficiency in Guinea Pigs on Intestinal Functions and Chemical Composition of Brush Border Membrane

A kinetic study of the interactions between amino acids and monosaccharides at the intestinal brush‐border membrane.

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