Pyochelin, an endogenous growth promoter that solubilizes ferric iron, has been isolated from Pseudomonas aeruginosa, including clinical strains. The structure of pyochelin has been assigned as 2-(2-o-hydroxyphenyl-2-thiazolin4-yl)-3-methylthiazolidine4-carboxylic acid and is of a different type from those previously assigned to siderophores (siderochromes) from bacteria. The assignment rests on H and '3C NMR data, highresolution (including field desorption) mass spectrometry, and spectroscopic properties ofsynthetic model compounds. Pyochelin is presumed to be biosynthesized from salicylic acid and two moles of cysteine.Many microorganisms produce compounds [siderophores (1) or siderochromes (2)] that bind iron and enhance microbial growth by solubilizing ferric iron and by accelerating iron transport. These compounds have been classified loosely as phenolate or hydroxamate siderophores according to the groups that are involved in forming the iron ligands. The phenolate siderophore studied most intensively, which is produced by Escherichia coli and Salmonella typhimurium and has been referred to as both enterochelin (3) and enterobactin (4), contains as its active site N-(2,3-dihydroxybenzoyl)serine (3, 4), which forms a trimer by ester bonds involving the serine hydroxyl groups. Phenolate siderophores appear to be produced exclusively by bacteria, whereas hydroxamates are produced by both bacteria and fungi. Bacteria usually synthesize dihydroxamates containing E-N-hydroxylysine, whereas fungi and streptomycetes usually synthesize trihydroxamates containing 8-N-hydroxyornithine, although exceptions are known (5). There is also the mixed case of mycobactin, the hypothesized siderophore of mycobacteria, which contains two hydroxamate groups in addition to a phenolate group consisting of salicylate or 6-methylsalicylate (6).An iron-binding compound has been isolated from culture media of Pseudoxnnnas aeruginosa (7, 8) containing <0. 1 uM ferric iron and shown to enhance the growth of the bacterium under iron-limiting conditions. The compound was phenolic rather than hydroxamic but was not a dihydroxybenzoate, and it accelerated the transport of 5Fe into bacteria (9). A similar or identical material also has been reported by others (10) and given the name pyochelin A. Growth promotion of P. aeruginosa is of particular clinical significance because of the organism's involvement in infection of severe bums (11), and several investigations have concluded that iron is important to the pathogenesis of the bacterium in experimental animals (12,13). In this connection, pyochelin was produced by all of the clinical isolates examined (8). The present report describes the properties of pyochelin and assigns its structure as 1, a structure MATERIALS AND METHODS Spectra. Low-resolution electron impact (LREI) mass spectra were obtained on a Varian MAT CH-5 DF spectrometer; high-resolution electron impact (HREI) and low-and high-resolution field desorption (FD) mass spectra were obtained on a Varian MAT 731 spectromete...

We have isolated a cDNA clone by screening a rabbit kidney cortex cDNA library for expression of sodiumindependent transport of L-arginine and L-alanine in Xenopus laevis oocytes. Expressed uptake relates to a single component of sodium-independent transport for dibasic and neutral amino acids. This transport activity resembles the functionally defined system b0'+ and carries cystine and dibasic amino acids with high affmity. The rBAT (bO'+ amino acid transporterrelated) mRNA is found mainly in kidney and intestinal mucosa. It encodes a predicted 77.8-kDa protein with only one putative transmembrane domain and seven potential N-glycosylation sites. This protein could either be a constitutive element or a specific activator of system b°'+.

A cDNA library from rabbit kidney cortex was screened for expression of Na-dependent transport of phosphate (P.) using Xenopus laevis oocytes as an expression system. A single clone was eventually isolated (designated NaPi-1) that stimulated expression of Na/P1 cotransport -700-fold compared to total mRNA. The predicted sequence of the Na/P1 cotransporter consists of 465 amino acids (relative molecular mass, 51,797); hydropathy profile predictions suggest six (possibly eight) membrane-spanning segments. In vitro translation of NaPi-1/complementary RNA in the presence of pancreatic microsomes indicated NaPi-1 to be a glycosylated protein; four potential N-glycosylation sites are present in the amino acid sequence. Northern blot analysis demonstrated the presence of NaPi-1/mRNA in kidney cortex and liver; no hybridization signal was obtained with mRNA from other tissues (including small intestine). Kinetic analysis of Na/P1 cotransport expressed by NaPi-1/complementary RNA demonstrated characteristics (sodium interaction) similar to those observed in cortical apical membranes. The alignment of 5 amino acid residues (Gly32/Alae'-Xaa-Xaa-Xaa-Xaa-Leu38-Xaa-XaaXaa-Pro3W.Arg39l) is consistent with a motif proposed for Na-dependent transport systems. We conclude that we have cloned a cDNA for a Na/P1 cotransport system present in rabbit kidney cortex.Reabsorption of phosphate (P) in the proximal tubule of the kidney contributes essentially to maintenance of the body Pi homeostasis (1). Influx of Pi at the brush border membrane of epithelial cells is mediated by a Na/Pt cotransporter and is driven by the transmembrane electrochemical potential gradient of sodium (2). Thereafter, P1 moves to the blood across the basolateral membrane, most likely via an anion-exchange mechanism and/or another Na-dependent Pi transport system. This transepithelial transport of P1 is controlled in a complex manner by various hormonal (e.g., parathyroid hormone) and nonhormonal (e.g., dietary Pi/Pi demand) factors (2-4).By using different experimental systems such as isolated tubules, isolated brush border membranes, and established cell cultures, it has been demonstrated that regulation of proximal tubular Pi reabsorption is accomplished mainly by modulation of the apically localized Na/Pi cotransport system (2). Thus, this Na/Pa cotransport system is a central target within the complex control of P1 homeostasis. Studies with established cell lines (mainly opossum kidney cells) demonstrated that inhibition of the Na/Ps cotransport (by, for example, parathyroid hormone) is mediated by activation of protein kinase C and/or A followed by an internalization step (endocytosis) of the transport system. On the other hand, stimulation of Na/P, cotransport by, for example, reduction of the concentration of extracellular Pi has been demonstrated to be dependent on de novo protein synthesis (2, 5).Despite the detailed knowledge of kinetic and regulatory properties of the renal (proximal tubular) Na/Pa cotransport system and despite several bioc...

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