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Microvillus membrane differentiation: quantitative difference in cholera toxin binding to the intestinal surface of
Abstract:
Microvillus membranes (MVM) were isolated from newborn and adult New Zealand rabbit small intestine. The isolation procedure provided a mean enrichment of 25 +/- 4 for sucrase activity in adult preparations and of 27 +/- 3 for lactase activity in newborn preparations. These purified MVM were incubated with increasing concentrations of 125I-labeled cholera toxin (CT). 125I-CT binding to adult MVM reached saturation at 6.4 X 10(-9) M; in contrast 125I-CT binding to newborn MVM did not reach saturation but instead continued to increase with increasing 125I-CT concentrations. Scatchard plot analysis of adult data supported the existence of a single binding site (Kd = 1.2 +/- 0.2 X 10(-9) M); analysis of newborn data, however, suggested the existence of additional binding sites, as 125I-CT binding to newborn MVM was inhibited by preincubation with unlabeled CT. These results show that CT binding to both preparations is quantitatively different and is higher in newborn preparations. This difference may be accounted for by the existence of additional binding sites in newborn MVM preparations in contrast to the presence of only the unique receptor previously reported in adult MVM preparations.
Insights
Cholera toxin (CT) binds differently to microvillus membranes (MVM) from newborn and adult rabbits. Newborn MVM show higher CT binding due to additional binding sites, unlike adult MVM.
Area of Science:
- Gastroenterology
- Biochemistry
- Molecular Biology
Background:
- Microvillus membranes (MVM) are crucial for nutrient absorption in the small intestine.
- Cholera toxin (CT) is a potent enterotoxin that interacts with intestinal cells.
Purpose of the Study:
- To investigate the quantitative differences in cholera toxin (CT) binding to microvillus membranes (MVM) isolated from newborn and adult rabbits.
- To characterize the binding kinetics and identify potential binding sites for CT on MVM.
Main Methods:
- Isolation of MVM from newborn and adult New Zealand rabbit small intestine.
- Incubation of purified MVM with increasing concentrations of 125I-labeled cholera toxin (CT).
- Scatchard plot analysis to determine CT binding site characteristics.
Main Results:
- 125I-CT binding to adult MVM reached saturation, indicating a single binding site (Kd = 1.2 x 10^-9 M).
- 125I-CT binding to newborn MVM did not reach saturation and was higher than in adults.
- Scatchard analysis suggested additional binding sites for CT on newborn MVM, confirmed by inhibition studies.
Conclusions:
- Cholera toxin (CT) exhibits quantitatively different binding to microvillus membranes (MVM) between newborn and adult rabbits.
- Newborn MVM possess additional CT binding sites compared to adult MVM, which have a unique receptor.
- These findings highlight developmental differences in intestinal toxin receptor expression.