Electrogenic K+-basic amino-acid cotransport in the midgut of lepidopteran larvae |
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Authors: | Barbara Giordana Paolo Parenti Giorgio M Hanozet V Franca Sacchi |
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Institution: | (1) Dipartimento di Fisiologia e Biochimica Generali, Università di Milano, 20133 Milano, Italy |
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Abstract: | Summary Experiments performed on isolated midgut demonstrate that the model proposed for the absorption of neutral amino acids in the K+-transporting intestinal epithelium of lepidopteran larvae applies also to the transport of the basic amino acids histidine and lysine. The characteristics of these K+-basic amino-acid cotransports have been studied in brush-border membrane vesicles. Histidine and lysine are transported by different transport agencies, which share, to a different degree, a high sensitivity to transmembrane electrical potential difference. Kinetic analysis showed thatK
m
for histidine and lysine increased 10-fold and three-fold, respectively, whereasV
max was only slightly modified when the electrical potential difference was abolished. The relationship between potassium concentration and histidine uptake indicates a cooperative binding of more than one potassium to the transporter. Countertransport experiments with glutamine as elicitor show that histidine and glutamine are transported through the same system. |
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Keywords: | lepidopteran larvae midgut basic amino-acid transport K+ cotransport transstimulation brush-border membrane vesicles |
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