SUBSTRATE STRUCTURE AND AMINO-ACID K-BORDER MEMBRANE-VESICLES FROM LARVAL MANDUCA-SEXTA MIDGUT( SYMPORT IN BRUSH)

Citation
R. Parthasarathy et al., SUBSTRATE STRUCTURE AND AMINO-ACID K-BORDER MEMBRANE-VESICLES FROM LARVAL MANDUCA-SEXTA MIDGUT( SYMPORT IN BRUSH), Journal of Experimental Biology, 197, 1994, pp. 237-250
Citations number
29
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Biology
ISSN journal
0022-0949
Volume
197
Year of publication
1994
Pages
237 - 250
Database
ISI
SICI code
0022-0949(1994)197:<237:SSAAKM>2.0.ZU;2-K
Abstract
The effects of amino acid sidechain length, substituent position and c hirality on amino acid/K+ symport have been examined in rapid filtrati on experiments on brush-border membrane Vesicles prepared from larval Manduca sexta midgut. Cis-inhibition and trans-stimulation protocols w ere used to examine the effects of amino acid analogs on the uptake of alanine, phenylalanine, leucine and lysine, which are cotransported w ith K+ by a zwitterionic symporter at the high pH characteristic of th e midgut in vivo. The symporter was found to translocate both L- and D -stereoisomers of alanine, leucine and lysine, but only the L-form of phenylalanine. Alterations to substrate structure that leave the charg e distribution unchanged do not affect symport. Thus, moving the methy l group from C-3 to C-5 in the sequence isoleucine, leucine and norleu cine has no effect on their ability to inhibit leucine symport. Increa sing sidechain length among alanine homologs has little effect on thei r ability to inhibit alanine uptake, but increasing the sidechain leng th of lysine homologs from 1 to 3 methylene groups enhances cis-inhibi tion and trans-stimulation of lysine symport. The substantial. differe nce in molecular charge distribution among aminobutanoic acid isomers has a large impact on alanine symport with only alpha- (or 2-) aminobu tanoic acid functioning as an alanine analog. Only those changes in su bstrate structure that are coupled to the molecular charge distributio n seem to affect symport. The tolerance of the symporter may reflect a balance mandated by the conflicting demands of selectivity and throug hput.