A full-length cDNA for a membrane transporter was isolated from Brassica napus by its sequence homology to a previously cloned Arabidopsis low affinity nitrate transporter. The cDNA encodes a predicted protein of 589 amino acid residues with 12 putative transmembrane domains. The transporter belongs to a multigene family with members that have been identified in bacteria, fungi, plants, and animals and that are able to transport a range of different nitrogen-containing substrates, including amino acids, peptides, and nitrate. To identify the substrates of this plant gene, we have expressed the protein in Xenopus oocytes. The properties of the transporter are consistent with a proton cotransport mechanism for nitrate, and the voltage dependence of the K m for nitrate was determined. The K m for nitrate was shown to increase from 4 to 14 mM as the membrane voltage became more negative from ؊40 to ؊180 mV. Oocytes expressing the gene could accumulate internal nitrate to concentrations higher than those measured in water-injected controls. A range of different substrate molecules for the transporter was tested, but of these, histidine gave the largest currents, although the affinity was in the millimolar range. The pH dependence of the activity of the transporter was different for the substrates, with histidine transport favored at alkaline and nitrate at acid external pH. Kinetic analysis of the mechanism of histidine transport suggests a cotransport of protons and the neutral form of the amino acid, with the K m for histidine decreasing at more negative membrane voltages. This gene is the first member of this family of transporters for which the transport of two very different types of substrate, nitrate and histidine, has been demonstrated.A family of mammalian peptide transporters (1, 2) has been identified, and sequence comparisons have shown that it includes plant peptide transporters (3-5). The mammalian peptide transporters have been shown to transport a broad range of substrates, including di-and tripeptides (2) and free amino acids (6). The family members are characterized by all having a consensus motif, and they have been named the proton-dependent oligopeptide transporter (POT) family (7), or as most members are peptide transporters, they have also been called the PTR family (8). However, the family also includes plant members that have been identified as nitrate transporters (9, 10). In this paper, we show that another member of this family, isolated from the plant Brassica napus, can transport both the amino acids and nitrate when expressed in Xenopus oocytes.In soil, the nitrate concentrations can vary from Ͼ1 M to Ͼ10 mM depending on factors such as rainfall and fertilizer supply (11). Soil also contains other forms of nitrogen, including ammonium and amino acids, and these may also be nitrogen sources available to plants (e.g. Ref. 12). Nitrate uptake by plants has been shown to have biphasic kinetics, with different affinities for external nitrate; one uptake system has K m values for nitrate in t...

We conclude that genetic analysis using Pyrosequencing trade mark technology was nonlaborious, and gave highly accurate data for different kinds of target. We therefore believe that this technology has the potential to complement or in the future substitute the time-consuming traditional microbial identification and typing methods, as well as enabling rapid typing of relevant host genetic markers.

Several abnormalities of cation transport have been described in the Milan hypertensive rats (MHS). In this study we examined Na,K-ATPase activity in proximal convoluted tubules (PCT) cells and medullary thick ascending limb of Henle cells (TAL) from MHS and from the Milan normotensive rats (MNS). Na,K-ATPase activity was determined as 32P-ATP hydrolysis in single tubule segments. Na,K-ATPase activity (pmol Pi/mm t/h) was significantly higher in MHS than MNS both in PCT (903 +/- 227 n = 8 v 506 +/- 285 n = 12) and TAL (4324 +/- 800 n = 5 v 3063 +/- 625 n = 5). Na,K-ATPase dependent respiration was determined in PCT cell from MNS and MHS. Under basal condition Na,K-ATPase dependent respiration (mumol O2/mg protein/h) was higher in MHS than in MNS (24.2 +/- 1.8 n = 5 v 16.1 +/- 0.4 n = 5). When the cells were Na loaded by amphotericin Na,K-ATPase dependent respiration increased significantly more in MHS than MNS (38.4 +/- 1.6 v 26.8 +/- 2.2 n = 4). Thus, Na,K-ATPase activity is higher in renal tubule cells both at normal intracellular Na and after the cells have been Na loaded. The results indicate that regulation of Na homeostasis in renal tubule cell is different in MHS and MNS.