The transport of Krebs-cycle intermediates in Azotobacter vinelandii under various metabolic conditions

Distinct metabolic profile of primary focal segmental glomerulosclerosis revealed by NMR-based metabolomics

Background

Primary focal segmental glomerulosclerosis (FSGS) is pathological entity which is characterized by idiopathic steroid-resistant nephrotic syndrome (SRNS) and progression to end-stage renal disease (ESRD) in the majority of affected individuals. Currently, there is no practical noninvasive technique to predict different pathological types of glomerulopathies. In this study, the role of urinary metabolomics in the diagnosis and pathogenesis of FSGS was investigated.

Methods

NMR-based metabolomics was applied for the urinary metabolic profile in the patients with FSGS (n = 25), membranous nephropathy (MN, n = 24), minimal change disease (MCD, n = 14) and IgA nephropathy (IgAN, n = 26), and healthy controls (CON, n = 35). The acquired data were analyzed using principal component analysis (PCA) followed by orthogonal projections to latent structure discriminant analysis (OPLS-DA). Model validity was verified using permutation tests.

Results

FSGS patients were clearly distinguished from healthy controls and other three types of glomerulopathies with good sensitivity and specificity based on their global urinary metabolic profiles. In FSGS patients, urinary levels of glucose, dimethylamine and trimethylamine increased compared with healthy controls, while pyruvate, valine, hippurate, isoleucine, phenylacetylglycine, citrate, tyrosine, 3-methylhistidine and β-hydroxyisovalerate decreased. Additionally, FSGS patients had lower urine N-methylnicotinamide levels compared with other glomerulopathies.

Conclusions

NMR-based metabonomic approach is amenable for the noninvasive diagnosis and differential diagnosis of FSGS as well as other glomerulopathies, and it could indicate the possible mechanisms of primary FSGS.

Alteration of glucose transport and diauxic growth in 5-thio-D-glucose-resistant mutants of Azotobacter vinelandii

Spontaneous mutants of Azotobacter vinelandii defective for glucose utilization were selected as resistant to 5-thio-D-glucose. Mutant strains AM2, AM38, and AM39 exhibited longer generation times than the wild type when grown on glucose. Mutant strain AM2 also exhibited an altered Km and Vmax for glucose uptake. During acetate-glucose diauxie, glucose utilization in the 5-thio-D-glucose-resistant mutants was subject to severe inhibition by acetate. These mutants did not exhibit the normal glucose phase of diauxie. Transport studies during diauxie indicated that glucose uptake was not induced in mutant strain AM2. However, increasing the glucose concentration from 25 to 200 mM relieved the severe acetate inhibition, and under these conditions the mutant strain AM2 exhibited normal diauxie. Revertants of mutant strain AM2 exhibited normal glucose and diauxie growth. The results are discussed in terms of a model for acetate regulation of glucose utilization in A. vinelandii.

Effect of triethyltin on Escherichia coli K-12

Triethyltin (TET) stimulated the basal respiration of Escherichia coli K-12 membrane vesicles in chloride (Cl-) medium but it had little effect on respiration in sulphate (SO4(2-)) medium. Since this uncoupling activity was Cl- dependent it was attributed to the Cl-/hydroxide (OH-) exchange reaction known to be mediated by TET [1,2]. TET inhibited the oxidation of succinate by intact E. coli in both Cl- and SO4(2-) medium, but at the same concentration of TET, inhibition was always more extensive in Cl- than SO4(2-) medium. In Cl- medium uncoupling in membrane vesicles and inhibition of succinate oxidation in intact bacteria occurred over the same concentration range and it appeared that the same mechanism, i.e. Cl-/OH- exchange, was responsible for both effects. Inhibition of succinate oxidation in SO4(2-) medium was not substantial until the concentration of TET was greater than 10(-5) M. Although the nature of this inhibition could not be determined by experiments with membrane vesicles indirect evidence from growth experiments indicated that it was due to impairment of oxidative phosphorylation. The relationship between these biochemical findings and the bacteriocidal action of TET was examined by using various concentrations of anion and substrate in the growth medium. Growth was inhibited in media containing either Cl- or SO4(2-) as the main anion but at a particular concentration of TET, inhibition was greater in Cl- medium. Growth was also inhibited to a greater extent in succinate than glucose medium. Furthermore in either Cl- or SO4(2-) glucose medium, lactic acid production increased as the concentration of TET was increased. These findings imply that the bacteriocidal action of TET is related to its effect(s) on oxidative phosphorylation.

Accumulation of arsenate, phosphate, and aspartate by Sreptococcus faecalis

Uptake of arsenate and phosphate by Streptococcus faecalis 9790 is strictly dependent on concurrent energy metabolism and essentially unidirectional. targinine supports uptake only in presence of glycerol or related substances; glycerol is not directly involved in transport but depletes the cellular orthophosphate pool and thus relieves feedback inhibition of transport. Uptake of phosphate and arsenate is stimulated by K+ and by other permeant cations. The results suggest that electroneutrality is preserved by compensatory movement of either H+ or OH minus. Ionophores and N,N'-dicyclohexylcarbodiimide, which prevent establishment of a proton motive force, block the accumulation of thiomethylgalactoside and of threonine but not that of arsenate or phosphate. We conclude that arsenate accumulation requires adenosine 5'-triphosphate but is not driven by the proton-motive force. However, conditions and reagents that lower the cytoplasmic pH do inhibit accumulation of arsenate and phosphate, suggesting that uptake depends on the capacity of the cells to maintain a neutral or alkaline cytoplasm. We therefore propose that phosphate accumulation is an electroneutral exchange for OH driven by adenosine 5'-triphosphate or by a metabolite thereof. Accumulation of aspartate and glutamate also requires adenosine 5'-triphosphate but not the proton-motive force and may involve a similar mechanism.

Effect of dicyclohexylcarbodiimide on growth and membrane-mediated processes in wild type and heptose-deficient mutants of Escherichia coli K-12

The effects of N,N'-dicyclohexylcarbodiimide (DCCD) on the growth of Streptococcus faecalis, and on the growth, beta-galactosidase synthesis, and various membrane-mediated processes, were studied in wild-type Escherichia coli JE1011 and its lipopolysaccharide-defective mutant NS1. DCCD (0.1 mM) completely inhibited the growth of S. faecalis and E. coli NS1 but had little effect on strain JE1011. The same amount of DCCD with E. coli NS1, but not with E. coli JE1011, inhibited the induction of beta-galactosidase, increased the permeability of the cells to o-nitrophenyl-beta-d-galactoside without causing extensive cell lysis or release of ultraviolet-absorbing materials, and inhibited the oxidation of certain intermediates of the tricarboxylic acid cycle. Inhibition of the oxidation of malate, fumarate, and alpha-ketoglutarate by DCCD appeared to be at the level of the transport system for these compounds. Inhibition of the membrane-bound adenosine triphosphatase by DCCD was not entirely responsible for these effects, since oxidation of these substances, and transport of [(14)C]succinate and [(14)C]fumarate, was inhibited by DCCD in a mutant, N(144), which lacked adenosine triphosphatase activity. It is concluded that lipopolysaccharide forms a barrier to DCCD in wild-type E. coli, and that DCCD can inhibit several processes in the cell.