title: Lipid and temperature dependence of the kinetic and thermodynamic parameters for active amino acid transport in Escherichia coli K1060.
abstract: The influence of membrane physical state on the kinetic and thermodynamic parameters for the active transport systems for two amino acids has been investigated in Escherichia coli K1060, an unsaturated fatty acid auxotrophic mutant. The apparent Michaelis constant (Km) for the uptake of L-[14C]glutamine (0.05 to 0.08 microM) or L-[14C]proline (1 microM approx.) is invariant with temperature for this mutant grown on elaidate (18:1t), palmitelaidate (16:1t), oleate (18:1c), palmitoleate (16:1c) and linoleate (18:2c,c). Arrhenius plots of the maximum velocities (Vmax) for L-glutamine transport in cells grown on 16:1t, 18:1c and 16:1c are biphasic within a limited temperature range peculiar to each UFA supplementation. Above an upper temperature limit also displayed by 18:1t and 18:2c,c-cells, Vmax decreases with temperature. A characteristic temperature (Tb) marks the point of intersection of the biphasic slope of the Arrhenius plots, and activation energy (Ea) is lower above than below Tb. Differential thermal analysis considered with membrane lipid fatty acyl profiles indicates that the upper temperature limit is governed by both membrane lipid acyl chain fluidity and heterogeneity, while Tb is governed by fluidity alone. Data on L-proline transport Vmax are similar, but the upper temperature limit and Tb are each shifted to lower temperatures relative to L-glutamine. We suggest that membrane defects related to energy-coupling and caused by abnormal fluidity and physical state are responsible for the peculiar temperature dependences of Vmax for these active transport processes.
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D004926:Escherichia coli / Q000378:metabolism*; D005227:Fatty Acids / Q000494:pharmacology / Q000502:physiology*; D005973:Glutamine / Q000378:metabolism; D007700:Kinetics; D008563:Membrane Lipids / Q000502:physiology*; D011392:Proline / Q000378:metabolism; D013696:Temperature; D013816:Thermodynamics
chemical_list: D000596:Amino Acids; D005227:Fatty Acids; D008563:Membrane Lipids; D005973:Glutamine; D011392:Proline