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PubMed1992

Effect of ionic strength and pH on the activity of pyruvate dehydrogenase complex from pig kidney cortex.

The activity of pyruvate dehydrogenase complex (PDC) purified from pig kidney cortex is sensitive to changes in ionic strength (mu). At low ionic strength (mu = 0.04 M) the specific activity of PDC was 12.22 mumol/min/mg, whereas at high ionic strength (mu = 0.15 M) the measured activity of the complex decreased to 4.88 mumol/min/mg. The optimum activity of PDC was achieved within a small range of ionic strength, mu = 0.035-0.040 M. Increasing the ionic strength from mu = 0.05 to mu = 0.15 M decreased the s0.5 for pyruvate from 125 to 72 microM and increased the Hill coefficient from 1.0 to 1.3. The effect of pH on PDC activity also was dependent upon ionic strength. At pH 7.2 the activity of PDC at mu = 0.05 and mu = 0.15 M was 90 and 55% of the maximal activity, respectively. Furthermore, the effects of Na+, K+, HCO3-, Cl-, and HPO4(2-) on PDC activity were dependent on ionic strength and pH. The addition of K+ (80 mM) at mu = 0.10 and mu = 0.15 M increased the activity of PDC by 12 and 42%, respectively. Lowering the pH from 8.2 to 7.5 resulted in a decrease in the s0.5 for pyruvate from 179 to 110 microM and from 110 to 35 microM in the presence and absence of K+ (80 mM), Na+ (20 mM), Cl- (20 mM), HCO3- (20 mM), and HPO4(2-) (10 mM), respectively. The observed changes in the properties of PDC in response to changes in ionic strength likely was a result of changes in the intramolecular electrostatic interactions within the complex. In this regard it was determined using two-dimensional agarose gel electrophoresis of the intact multienzyme complex that increasing the ionic strength to which PDC is exposed decreased the measured radius of PDC and may have decreased the electronegative surface charge of the complex.

Animals↗
PubMed1993

Subcellular distribution and guanine nucleotide dependency of COOH-terminal methylation in kidney cortex.

The subcellular distribution of COOH-terminal carboxyl methyltransferase and methylated substrates was studied in purified brush-border and basolateral plasma membranes, as well as in crude intracellular membranes and the cytosolic fraction isolated from rat kidney cortex. The three membrane fractions showed intrinsic carboxyl methylation of 21- to 23-kDa proteins, whereas 18- and 41-kDa methylated proteins were observed in the cytosol. In contrast, methylation activities toward N-acetyl-S-trans,trans-farnesyl-L-cysteine (AFC), a synthetic farnesylated substrate, were found to be strictly associated with membranes, with no detectable level of activity in the cytosol. Methylation of all membrane-associated substrates was inhibited by AFC but remained unaffected by TS-isoD-YSKY, a synthetic isopeptide recognized by L-isoaspartyl methyltransferase, suggesting that the membrane-associated substrates were methylated on a COOH-terminal isoprenylated cysteine residue. The membrane-associated methylated proteins were tightly bound to the membranes as reflected by their extraction with 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate but not with 1 M NaCl or 2 M urea. The nonhydrolyzable analogues of GTP and GDP, guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) and guanosine 5'-O-(2-thiodiphosphate) (GDP beta S), markedly increased the methylation of the 21- to 23-kDa substrates, whereas ATP gamma S and ADP beta S were without effect. This effect of guanine nucleotides was restricted to endogenous 21- to 23-kDa substrates with no stimulation of methylation of the exogenous substrate, AFC. Our results show a wide distribution of both COOH-terminal protein carboxyl methyltransferase activities and associated methylated substrates in the kidney cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcysteine↗
PubMed1995

Opposite effects of polyamines on glutamate deamination in isolated renal tubules and permeabilized kidney cortex mitochondria of rabbit.

The effect of polyamines on glutamate deamination has been studied in both isolated tubules and permeabilized kidney cortex mitochondria of rabbit. Spermine, spermidine and putrescine resulted in a decrease of ammonium release in isolated renal tubules incubated with glutamate in the presence of MSO and AOA, inhibitors of glutamine synthetase and aminotransferases, respectively. This was not due to the inhibition of glutamate transport across renal tubular membranes since transport of [14C]glutamate into brush border membranes vesicles was not decreased by polyamines. In contrast, polyamines stimulated glutamate deamination in permeabilized mitochondria. This effect was additive to the action of ADP, an allosteric activator of glutamate dehydrogenase. Since these compounds decreased both glutamate-induced mitochondrial swelling as well as [14C]glutamate accumulation in mitochondria, the inhibitory effect of polyamines on glutamate deamination in renal tubules might be due to a diminished glutamate transport across the mitochondrial membrane.

Animals↗
PubMed1999

Ribose 1,5-bisphosphate regulates rat kidney cortex phosphofructokinase.

Phosphofructokinase (EC 2.7.1.11) is a major enzyme of the glycolytic pathway, catalyzing the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate. In this study, we demonstrated the effect of ribose 1,5-bisphosphate on phosphofructokinase purified from rat kidney cortex. Ribose 1,5-bisphosphate relieved the phosphofructokinase from ATP inhibition and increased the affinity for fructose 6-phosphate at nanomolar concentrations. These activating effects of ribose 1,5-bisphosphate were enhanced in the presence of AMP. Ribose 1,5-bisphosphate reduced the inhibition of the phosphofructokinase induced by citrate. These results suggest that ribose 1,5-bisphosphate is an activator of rat kidney cortex phosphofructokinase and synergistically regulates the enzyme activity with AMP.

Adenosine Monophosphate↗
PubMed1966

Energy barriers to sodium extrusion from sodium-rich kidney cortex slices.

1. Rat and guinea-pig kidney cortex slices were made Na-rich by leaching in cold NaCl and then allowed to recover in Ringer solution at 30 or 25 degrees C. Net Na extrusion was systematically decreased by the use of re-immersion media with constant Na and diminishing K, or with constant K and increasing Na, and the energy requirements for Na extrusion under these conditions were calculated.2. The critical energy barrier at which no net Na loss can be achieved was somewhat lower in these tissues than found by other authors for frog sartorius muscle.3. Inclusion of pyruvate or insulin and lactate in the recovery fluid had no effect.4. Methylsulphate apparently enters renal cells during incubation and is therefore unsuitable for use with this tissue as a source of impermeant anion.

Animals↗
PubMed1982

Effects of lipid peroxidation, Ca2+ and adrenalin on the release of fatty acids from rabbit kidney cortex slices.

Ascorbic acid (1 mM) plus Fe2+ (0.4 mM) and Ca2+ (4 mM) stimulated the release of arachidonic acid from rabbit kidney cortical slices. The release of arachidonic acid was inhibited completely by the addition of mepacrine (1.6 mM). Adrenalin (0.8 mM) enhanced the release of individual free fatty acids (C16:0, C18:0, C18:1, C18:2 and C20:4). The release of fatty acids by adrenalin was not inhibited by mepacrine (1.6 mM), but was inhibited by p-chloromercuribenzoic acid (2 mM). These results suggest that the lipolytic process in kidney cortex may be mediated either through the activation of phospholipase A2 by Ca2+ and ascorbic acid plus Fe2+ or through an adrenalin-activated lipase system.

Adipose Tissue↗
PubMed1970

Gluconeogenesis in the kidney cortex. Flow of malate between compartments.

1. Kidney-cortex slices from starved rats were incubated with l-[U-(14)C]lactate or l-[U-(14)C]malate plus unlabelled acetate and the specific radioactivity of the glucose formed was determined. In parallel experiments the specific radioactivity of the glucose formed from [1-(14)C]acetate plus unlabelled l-lactate and l-malate was determined. 2. By analytical methods the major products formed from the substrates were measured. The glucose formed was purified by paper chromatography for determination of specific radioactivity. 3. The specific radioactivity of the glucose formed from l-[U-(14)C]lactate agrees with predictions of a model based on interaction of the gluconeogenic and the oxidative pathways. 4. The specific radioactivity of the glucose formed from l-[U-(14)C]malate agrees with the predicted value if rapid malate exchange between the cytosol and mitochondria is assumed. 5. The rate of malate exchange between compartments was estimated to be rapid and at least several times the rate of glucose formation. 6. The specific radioactivity of the glucose formed from [1-(14)C]acetate plus unlabelled l-lactate or l-malate agrees with the predictions from the model, again assuming rapid malate exchange between compartments. 7. Malate exchange between compartments together with reversible malate dehydrogenase activity in the mitochondria and cytosol also tends to equilibrate isotopically the NADH pool in these compartments. (3)H from compounds such as l-[2-(3)H]lactate, which form NAD(3)H in the cytosol, appears in part in water; and (3)H from dl-beta-hydroxy[3-(3)H]butyrate, which forms NAD(3)H in the mitochondria, appears in part in glucose, largely on C-4.

Acetates↗
PubMed1975

The regulation of phosphoenolpyruvate carboxykinase (GTP) synthesis in rat kidney cortex. The role of acid-base balance and glucocorticoids.

The effects of metabolic acidosis and of hormones on the activity, synthesis, and degradation of renal cytosolic P-enolpyruvate carboxykinase (GTP) (EC 4.1.1.32) were studied in the rat using isotopic -immunochemical procedures. At normal acid-base balance, the synthesis of the enzyme accounted for between 2 and 3.5% of the synthesis of all soluble protein in the kidney cortex. P-enolpyruvate carboxykinase synthesis was selectively stimulated in acute metabolic acidosis, so that the relative rate of synthesis of the enzyme was increased to 7% 13 hours after oral administration of ammonium chloride. The stimulation of P-enolpyruvate carboxykinase synthesis preceded any increase in the assayable activity of the enzyme. The administration of sodium bicarbonate to acutely acidotic rats returned the rate of enzyme synthesis to normal in 8 hours. The effect of acidosis on both the synthesis and the activity of P-enolpyruvate carboxykinase was prevented by actinomycin D, cordycepin, and cycloheximide. The degradation in vivo of pulse-labeled P-enolpyruvate carboxykinase was not affected by acidosis. Thus, the stimulation of P-enolpyruvate carboxykinase synthesis is the major mechanism for the increase in the level of the enzyme observed in metabolic acidosis. The administration of glucocorticoid triamcinolone resulted in an increase in the relative rate of P-enolpyruvate carboxykinase synthesis and a commensurate increase in the activity of the enzyme in the renal cortex. Both changes were abolished by actinomycin D. Fasting was characterized by a high enzyme activity and a rapid rate of enzyme synthesis in the kidney cortex. This high rate of synthesis was reduced after the administration of sodium bicarbonate, but not after glucose feeding. Moreover, the injection of insulin to diabetic rats did not repress P-enolpyruvate carboxykinase synthesis in the renal cortex. Theophylline plus N-6, 0-2'-dibutyryl adenosine 3':5'-monophosphate stimulated P-enolpyruvate carboxykinase synthesis in the kidney of intact rats. However, the latter effect was probably due to glucocorticoid secretion, since it did not occur in adrenalectomized animals. The administration of parathyroid extracts did not result in the induction of the enzyme. Thus, the hormonal regulation of cytosolic P-enolpyruvate carboxykinase synthesis in the kidney differs markedly from that in the liver.

Acidosis↗
PubMed1984

Characterization of intermediate-molecular-weight acid phosphatase from bovine kidney cortex.

The distribution of acid phosphatases of intermediate molecular weight was determined in various mammalian tissues. The intermediate-molecular-weight acid phosphatases (designated P-II-1 and 2) comprised about 25% of the p-nitrophenyl phosphatase activity in the supernatant of bovine kidney cortex homogenate. The P-II-1 and 2 purified 2,000 fold showed the pI values of 5.9 and 5.7, respectively, on isoelectric focusing. Apparent molecular weights of both P-II-1 and 2 were estimated to be 42,000 by Sephadex G-100 gel filtration and 44,000 by SDS-polyacrylamide disc gel electrophoresis. Both the enzymes catalyzed the hydrolysis of a wide variety of natural phosphomonoesters, except for the phosphoproteins phosphoserine and o-phosphocholine. The enzymes showed a high activity on pyridoxal phosphate, beta-glycerophosphate, and 2'-AMP. The optimum activity pH was near 5 with p-nitrophenyl phosphate, but was shifted to the neutral range when pyridoxal phosphate was the substrate. The cations Hg2+ and Ag+ had a marked inhibitory effect. Neither enzyme was inhibited significantly by L-(+)-tartrate or pCMB. The two other types of acid phosphatases, the high-molecular-weight (designated P-I) and low-molecular-weight (designated P-III), were also purified to homogeneity from bovine kidney cortex, and were compared with P-II from several aspects including substrate specificity and susceptibility to various compounds.

Acid Phosphatase↗
PubMed2005

Cephaloridine induces translocation of protein kinase C delta into mitochondria and enhances mitochondrial generation of free radicals in the kidney cortex of rats causing renal dysfunction.

We have previously reported that the enhancement of free radical generation in mitochondria isolated from the kidney cortex of rats exposed to cephaloridine (CER) is probably mediated by the activation of protein kinase C (PKC). We examined which isoenzymes of PKC might be involved in the development of nephrotoxicity induced by CER in rats. The CER-induced renal dysfunction observed 24 h after its injection was prevented by a potent antioxidant DPPD and well-known PKC inhibitors like H-7 and rottlerin. At 1.5 and 3.5 h after the CER injection, the free radical generation was increased markedly and this was associated with translocation of PKCdelta into the mitochondria of renal cortex tissue. Pretreatment of rats with H-7, a PKC inhibitor, significantly inhibited the CER-derived increase in mitochondrial generation of free radicals, suggesting that H-7 probably gets into the mitochondria and inhibits the activity of translocated PKC within the mitochondria. It was also shown that pretreatment of rats with rottlerin, a specific inhibitor of PKCdelta, suppressed the early translocation of PKCdelta into mitochondria and inhibited the CER-derived development of renal dysfunction. These results suggest that the CER-derived early translocation of PKCdelta into mitochondria probably leads to the enhanced production of free radicals through the mitochondrial respiratory chain during the development of the nephrotoxicity caused by CER. Understanding the role of PKCdelta in mitochondria may provide an important clue to the molecular mechanisms of mitochondrial production of reactive oxygen species and the free radical-induced renal failure in rats treated with CER.

Animals↗
PubMed1994

Purification and some properties of a hydrophilic prokallikrein and a hydrophobic prokallikrein from sheep kidney cortex.

1. A hydrophilic and a hydrophobic prokallikrein were purified from sheep kidney cortex and some of their biochemical properties were compared. 2. The effects of several inhibitors on the activity of the hydrophilic and hydrophobic kallikreins were investigated. 3. The thermal stability and response of the hydrophobic kallikrein towards various detergents were also studied.

Animals↗
PubMed1989

Studies on the nephrotoxicity of aminoglycoside antibiotics and protection from these effects (7): Effect of latamoxef on binding of tobramycin to brush border membranes isolated from rat kidney cortex.

We investigated the effect of latamoxef (LMOX) on the binding of tobramycin (TOB) to brush border membranes (BBMs) isolated from rat kidney cortex by calcium precipitation. The simultaneous treatment with TOB (0.2 mM) and LMOX (10 and 20 mM) to the BBMs fraction (about 250 micrograms protein) significantly inhibited the binding of TOB to BBMs. The addition of the reaction mixture of TOB (0.2 mM) and LMOX (4, 10 and 20 mM) which was preincubated for 3 hr at 37 degrees C, to the BBMs fraction resulted in less binding of TOB to the membranes than that observed in the case of simultaneous treatment with both drugs. Although [14C]-labeled LMOX was taken up by BBMs temperature- and time-dependently, the pretreatment with LMOX showed no obvious differences in inhibition of the TOB binding to BBMs, as compared with the result from simultaneous treatment with both drugs. Additionally, the binding of TOB to the LMOX-treated BBMs that were resuspended in fresh medium after the pretreatment with LMOX for 10 min at 37 degrees C was similar to that of TOB to the non-treated BBMs. These results indicate that LMOX inhibits the binding of TOB to BBMs not by binding to BBMs but by interacting with TOB.

Animals↗
PubMed1978

[Activity of gluconeogenetic enzymes of rat kidney cortex during acute hypoxia].

The activities of gluconeogenic enzymes of the rat kidney cortex was studied after exposure to lowered atmospheric pressure (200 mm Hg) for 3 hours. The hypoxic stress was found to cause an increase in the activities of phosphoenolpyruvate carboxykinase and alanine aminotransferase, but failed to affect significantly the activities of fructose-1,6-diphosphatase, glucose-6-phosphatase, and aspartate aminotranspherase. The ratio of glucose-6-phosphatase/hexokinase activities was increased under these conditions.

Acute Disease↗
PubMed1989

Techniques for isolation of brush-border and basolateral membrane vesicles from dog kidney cortex.

Two methods are reported for renal membrane preparation from the dog kidney cortex. One method is a simultaneous preparation of brush-border (BBMV) and basolateral (BLMV) membranes. Using readily available laboratory equipment, differential centrifugation produced a supernatant which was treated with Mg2+. The Mg2+ treatment produced a pellet (crude BLMV) which was added to Percoll and centrifuged to produce purified BLMV. The supernatant after Mg2+ treatment eventually yielded pure BBMV after additional Mg2+ precipitations. The second method used an acidic medium in conjunction with divalent-cation precipitation to prepare BBMV. Whichever method was used, BBMV and BLMV showed appropriate enzyme and transport activities.

Animals↗
PubMed1990

Comparative studies of volume restoration following cold-stress induced swelling in renal tissues--I. Effects of ouabain, K+ free medium, colchicine and cytochalasin B on rat and rabbit kidney cortex slices.

1. Cold-stress-induced swelling in rabbit and rat kidney cortex slices cannot be due to the sole inhibition of a Na+/K+ exchange system. In these tissues indeed, ouabain induces no swelling and an exchange of Na+ for K+ or a l/l basis. Inhibition of K+ extrusion at low temperature has also to be taken into consideration. 2. Volume restoration at 27 degrees C after cold-stress-induced swelling is inhibited by ouabain in rabbit slices, not in rat ones. The inhibition in rabbit slices is concomitant with an increase in Na+ at levels higher than equilibrium with the external medium. 3. Volume restoration does not seem to implicate colchicine or cytochalasin B sensitive processes.

Animals↗
PubMed1977

Effect of cations on tetraehtylammonium exit from mouse kidney cortex slices.

Exit of 14C-tetraethylammonium (TEA) was studied in mouse kidney cortex slices incubated in Krebs-Ringer bicarbonate buffer (37 degrees C, pH 7.4) aerated with O2-CO295:5 v/v%. Substitution of Na+ in the wash out buffer by K+, Rb+ or the organic cations TEA and choline resulted in a stimulation of exit which, however, may be secondary to concomitant biochemical changes in the tissue (increase of water content and relative loss of K+) seen in the presence of these cations. However, enhancement of 14C-TEA exit although less pronounced was also produced of low organic cation concentrations having no effect on tissue water and K+. The latter specific effect on 14C-TEA exit may represent an interaction phenomenon in renal organic cation transport of accelerative exchange diffusion type.

Animals↗
PubMed1978

Properties of brush border vesicles isolated from rat kidney cortex by calcium precipitation.

Brush border membrane vesicles were isolated from rat kidney cortex by differential centrifugation in the presence of 10 mM calcium. Their properties were compared to brush border vesicles isolated by free-flow electrophoresis. By the calcium precipitation method membrane vesicles were obtained in a shorter time with a similar enrichment of brush border marker enzymes (11- to 12-fold for alkaline phosphatase and maltase), with a similarly reduced activity of the marker enzyme for basal-lateral plasma membranes and an almost identical protein composition as revealed by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. The transport properties of the two membrane preparations for D-glucose, L-phenylalanine, and phosphate are essentially the same; there is some indication for a lower sodium permeability of the vesicles prepared by the calcium precipitation method. The latter vesicles were also shown to exhibit sodium gradient stimulated uptake of L-glutamate.

Animals↗
PubMed1982

A study of the probenecid effect on amino acid accumulation in kidney cortex slices.

The amount of amino acids accumulated by rat and mouse kidney cortex slices is determined by both membrane transport and intracellular metabolism, especially protein incorporation. Even with substrate concentrations of 100 microM up to 70% of the transported amino acids were found to be protein incorporated. Probenecid reduces the accumulation of the amino acids glycine, L-phenylalanine, L-valine, L-arginine, L-lysine, L-proline and alpha-AIB. At substrate concentrations of 100 microM the inhibition is between 28 and 66% (except alpha-AIB) with a probenecid concentration of 7.0 mM. Slight inhibitory effects were observed with 0.7 mM probenecid. The probenecid effect, however, is mainly on the protein incorporation. With 7.0 mM probenecid protein incorporation is reduced considerably, for some amino acids below 10% of the control values; small inhibitory effects were observed with concentrations of 0.7 mM. Amino acid transport is affected only slightly by probenecid. In consequence, higher accumulation rates of free amino acids may be measured after probenecid administration, preferentially with amino acids showing high initial incorporation rates.

Amino Acids↗