TY - JOUR
T1 - Characterization of the double mutant, Val-177/Asn-322, of the lactose permease
AU - Brooker, Robert J.
N1 - Copyright:
Copyright 2007 Elsevier B.V., All rights reserved.
PY - 1990/3/5
Y1 - 1990/3/5
N2 - The double mutant, Val-177/Asn-322, was investigated with regard to its ability to transport H+ and galactosides. In downhill lactose transport assays, the wild-type strain had a Km value for lactose uptake of 0.9 mM and a Vmax of 0.65 μmol lactose/min·mg protein while the mutant had a significantly higher Km, value of 1.9 mM but a similar Vmax of 0.49 μmol/min·mg protein. In spite of its moderate ability to transport lactose downhill, the Val-177/Asn-322 mutant exhibited the striking property of being completely defective in the uphill accumulation of lactose or methyl-β-D-thiogalactopyranoside. Direct measurements of H+ transport, however, showed that the mutant's defect in active accumulation is not due to a defect in the ability to transport H+ with lactose or methyl-β-D-thiogalactopyranoside. The Val-177/Asn-322 mutant strain had a H+:lactose stoichiometry of 0.84 which was similar to that measured in the wild-type strain (0.68). These results are discussed with regard to the role His-322 plays in H+ transport, active accumulation of sugars, and sugar recognition.
AB - The double mutant, Val-177/Asn-322, was investigated with regard to its ability to transport H+ and galactosides. In downhill lactose transport assays, the wild-type strain had a Km value for lactose uptake of 0.9 mM and a Vmax of 0.65 μmol lactose/min·mg protein while the mutant had a significantly higher Km, value of 1.9 mM but a similar Vmax of 0.49 μmol/min·mg protein. In spite of its moderate ability to transport lactose downhill, the Val-177/Asn-322 mutant exhibited the striking property of being completely defective in the uphill accumulation of lactose or methyl-β-D-thiogalactopyranoside. Direct measurements of H+ transport, however, showed that the mutant's defect in active accumulation is not due to a defect in the ability to transport H+ with lactose or methyl-β-D-thiogalactopyranoside. The Val-177/Asn-322 mutant strain had a H+:lactose stoichiometry of 0.84 which was similar to that measured in the wild-type strain (0.68). These results are discussed with regard to the role His-322 plays in H+ transport, active accumulation of sugars, and sugar recognition.
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M3 - Article
C2 - 2406272
AN - SCOPUS:0025260988
SN - 0021-9258
VL - 265
SP - 4155
EP - 4160
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 7
ER -