title: A novel proline, glycine: K+ symporter in midgut brush-border membrane vesicles from larval Manduca sexta.
abstract: Alkali-cation-dependent uptake of proline and glycine into brush-border membrane vesicles from the midgut of the larval tobacco hornworm Manduca sexta was investigated using rapid filtration assays. Uptake of both amino acids was by electrophoretic symport, with K+ being the favored cation at pH 10. Counterflow accumulation of proline was elicited by glycine and vice versa, suggesting that the two amino acids are transported by a common symporter, which we designate the pro, gly: K+ symporter. L-alpha-Aminoisobutyric acid was the only other amino acid that elicited the accumulation of both proline and glycine. D-Proline was not symported; L-proline, glycine and L-alpha-aminoisobutyric acid appear to be the only substrates of the pro, gly: K+ symporter. Neutral amino acids with relatively short sidechains elicit glycine accumulation, suggesting that glycine may also be symported by the well-established neutral amino acid system. Since proline does not utilize the broad-spectrum, neutral system, its symport appears to be exclusively through the pro, gly: K+ symporter. Proline symport was found mainly in posterior midgut vesicles, suggesting that the pro, gly: K+ symporter may be localized in this region of the midgut.
authors.affiliation: Department of Biology, Temple University, Philadelphia, PA 19122, USA.
authors.forename: A L
authors.initials: AL
authors.lastname: Bader
authors.forename: R
authors.initials: R
authors.lastname: Parthasarathy
authors.forename: W R
authors.initials: WR
authors.lastname: Harvey
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism*; D005998:Glycine / Q000378:metabolism*; D017136:Ion Transport; D007814:Larva / Q000378:metabolism; D018402:Manduca / Q000378:metabolism*; D011392:Proline / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D011392:Proline; D005998:Glycine