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Journal of Experimental Biology 149,207-221 (1990)
Published by Company of Biologists 1990

LEUCINE UPTAKE IN BRUSH-BORDER MEMBRANE VESICLES FROM THE MIDGUT OF A LEPIDOPTERAN LARVA, PHILOSAMIA CYNTHIA

V. FRANCA SACCHI 1, BARBARA GIORDANA 2, FLAVIA CAMPANINI 2, PATRIZIA BONFANTI 2, and GIORGIO M. HANOZET 3

1 Istituto di Fisiologia Generate e di Chimica Biologica, Universita di Milano, Via Saldini 50,
2 Dipartimento di Biologia
3 Dipartimento di Fisiologia e Biochimica Generali, Universita di Milano, Via Celoria 26, Milano, Italy

A potassium- or sodium-activated cotransport of leucine occurs in brush-border membrane vesicles prepared from the midgut of larvae of Philosamia cynthia Drury). The potassium chemical gradient can drive a twofold accumulation of leucine, which is greatly increased under experimental conditions that presumably provide an electrical potential difference ({delta}{psi})

Kinetic parameters show that leucine transport is improved by these conditions and by a pH gradient similar to that occurring in vivo. However, these gradients cannot drive an intravesicular accumulation of leucine in the absence of potassium. The potassium-dependence of leucine uptake shows that 20% of the transport is potassium-independent and that K50 and Vmax are 30.3± 3.2mmoll-1 and 2584±148pmol 7 s-1mg-1 protein, respectively. The potassium-independent component of leucine transport is also carrier-mediated and some evidence is reported suggesting that the same carrier can cross the membrane as binary carrier and leucine) or ternary (carrier, leucine and potassium) complexes, each having a different mobility

Key words: leucine uptake, amino acid transport, brush-border membrane vesicles, insect nidgut

Accepted on October 19, 1989






© The Company of Biologists Ltd 1990