Leucine methyl ester is a powerful allosteric activator of the neutral amino acid cotransport system in Bombyx mori larval midgut.
We have identified three methyl esters that have a potent stimulatory effect on the cotransport system responsible for the absorption of most essential amino acids in the silkworm Bombyx mori. L-Leucine methyl ester, the most powerful activator, determined a large dose-dependent, K(+)-independent increase of leucine uptake into midgut brush border membrane vesicles. Kinetic experiments revealed non-essential mixed-type activation, with K(a) values of 27+/-2 and 47+/-8 microM in the presence and in the absence of K(+), respectively. The activation increased K(m) twofold, and V(max) up to 18-fold depending upon the experimental conditions. Leucine uptake mediated by the amino acid uniport appears to be unaffected by the activator.
Parenti
P
P
Department of Environmental Sciences, University of Milano-Bicocca, P.zza della Scienza 1, 20126, Milano, Italy. paolo.parenti@unimib.it
Leonardi
M G
MG
Forcella
M
M
Casartelli
M
M
Pugliese
A
A
Hanozet
G M
GM
Giordana
B
B
D000494:Allosteric Regulation; D026921:Amino Acid Transport Systems, Neutral / Q000378:metabolism*; D000818:Animals; D012831:Bombyx / Q000378:metabolism*; D004064:Digestive System; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007814:Larva; D007930:Leucine / Q000031:analogs & derivatives* / Q000378:metabolism*; D008871:Microvilli / Q000378:metabolism; D011188:Potassium / Q000378:metabolism
D026921:Amino Acid Transport Systems, Neutral; C030365:leucine methyl ester; D007930:Leucine; D011188:Potassium