scholarly journals Folate transport in intestinal brush border membrane: involvement of essential histidine residue(s)

1993 ◽  
Vol 290 (1) ◽  
pp. 237-240 ◽  
Author(s):  
H M Said ◽  
R Mohammadkhani
Keyword(s):  
Folic Acid ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Inhibitory Effect ◽  
Histidine Residue ◽  
Acid Transport ◽  
Intestinal Brush Border Membrane ◽  
Intestinal Brush Border ◽  
Rabbit Intestine

We examined the possible existence of histidine residue(s) in the folate transporter of rabbit intestine. This was done with use of the histidine-specific reagent diethyl pyrocarbonate (DEPC) and purified intestinal brush-border-membrane vesicles. DEPC caused significant concentration- and time-dependent inhibition of folic acid transport. The inhibition was only seen when transport was examined in vesicles incubated in buffer at pH 5.2 and not in those incubated in buffer at pH 7.4. The addition of unlabelled folic acid to vesicle suspension before treatment with DEPC (2.5 mM) led to a significant (P < 0.01) protection (84%) against the inhibition of folic acid transport. Treating vesicles pretreated with DEPC (2.5 mM) with reducing reagents (dithiothreitol, 2-mercaptoethanol and 2,3-dimercaptopropanol, all at a final concentration of 10 mM) did not reverse the inhibitory effect of DEPC on folic acid transport. On the other hand, treating the DEPC-pretreated vesicles with hydroxylamine (140 mM) led to a significant reversal (P < 0.01) (54%) of the inhibition of folic acid transport. The inhibitory effect of DEPC on carrier-mediated folic acid transport was found to be mediated through a decrease in the Vmax. (i.e. a decrease in the number and/or activity) of the carriers and an increase in the apparent Km (i.e. a decrease in their affinity), classifying the effect as a mixed-type inhibition. These results demonstrate the existence of critical histidine residue(s) in the intestinal brush-border-membrane folate transporter which is essential for its interaction with, and transport of, the vitamin. These findings also suggest that the histidine residue(s) is located at (or near) the substrate-binding site.

scholarly journals Direct Inhibitory Effect of Rotavirus NSP4(114-135) Peptide on the Na+-d-Glucose Symporter of Rabbit Intestinal Brush Border Membrane

2000 ◽  
Vol 74 (20) ◽  
pp. 9464-9470 ◽  
Author(s):  
Nabil Halaihel ◽  
Vanessa Liévin ◽  
Judith M. Ball ◽  
Mary K. Estes ◽  
Francisco Alvarado ◽  
...  
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Inhibitory Effect ◽  
Norwalk Virus ◽  
Coupled Transport ◽  
Intestinal Brush Border Membrane ◽  
Intestinal Brush Border

ABSTRACT The direct effect of a rotavirus nonstructural glycoprotein, NSP4, and certain related peptides on the sodium-coupled transport ofd-glucose and of l-leucine was studied by using intestinal brush border membrane vesicles isolated from young rabbits. Kinetic analyses revealed that the NSP4(114-135) peptide, which causes diarrhea in young rodents, is a specific, fully noncompetitive inhibitor of the Na+-d-glucose symporter (SGLT1). This interaction involves three peptide-binding sites per carrier unit. In contrast, the Norwalk virus NV(464-483) and mNSP4(131K) peptides, neither of which causes diarrhea, both behave inertly. The NSP4(114-135) and NV(464-483) peptides inhibited Na+-l-leucine symport about equally and partially via a different transport mechanism, in that Na+behaves as a nonobligatory activator. The selective and strong inhibition caused by the NSP4(114-135) peptide on SGLT1 in vitro suggests that during rotavirus infection in vivo, NSP4 can be one effector directly causing SGLT1 inhibition. This effect, implying a concomitant inhibition of water reabsorption, is postulated to play a mechanistic role in the pathogenesis of rotavirus diarrhea.

Divalent cations and vitamin B12 uptake by intestinal brush-border membrane vesicles

1980 ◽  
Vol 239 (6) ◽  
pp. G452-G456
Author(s):  
R. C. Beesley ◽  
C. D. Bacheller
Keyword(s):  
Vitamin B12 ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Divalent Cations ◽  
Intrinsic Factor ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Tetraacetic Acid ◽  
Intestinal Brush Border Membrane ◽  
Intestinal Brush Border

Brush-border membrane vesicles from hamster intestine were employed to investigate uptake (binding) of vitamin B12 (B12). Ileal vesicles took up 25 times more B12 than did jejunal vesicles. Uptake of B12 by ileal vesicles was dependent on intrinsic factor (IF) and required Ca2+. Increasing the Ca2+ concentration caused an increase in uptake of B12 reaching a maximum at approximately 8 mM Ca2+. At high Ca2+ concentrations, 6–8 mM, Mg2+ had little effect on uptake of B12. At low Ca2+ concentrations, up to 2 mM, Mg2+ stimulated B12 uptake. Mg2+, Mn2+, and, to a lesser extent, Sr2+ stimulated Ca2+-dependent B12 uptake, but Zn2+, Ba2+, Na+, K+, and La3+ did not. B12 was apparently not metabolized and was bound as IF-B12 complex, which could be removed with (ethylenedinitrilo)tetraacetic acid (EDTA). Our results suggest that two types of divalent cation reactive sites are involved in binding of IF-B12. One is Ca2+ specific. The other is less specific reacting with Mg2+, Mn2+, Sr2+, and perhaps Ca2+ itself, thereby stimulating Ca2+-dependent binding of IF-B12 to its ileal receptor.

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