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PubMed1994

Cytosolic proteins of 21-23 kDa are methylated by kidney cortex membrane-associated C-terminal carboxyl methyltransferases.

We have studied the effect of a soluble fraction from kidney cortex on the C-terminal carboxyl methylation of 21-23 kDa proteins catalyzed by membrane-associated methyltransferases. Addition of soluble proteins to isolated luminal, antiluminal and intracellular membranes resulted in a large increase in the methylation of the membrane-associated 21-23 kDa substrates. Fractionation of the soluble extract from the cortex by Q-Sepharose anion exchange chromatography showed the presence of two distinct peaks of proteins presenting stimulating activities, eluting at 0.15 M (peak I) and 0.4 M (peak II) NaCl, respectively. Both peaks eluted as proteins of apparent molecular sizes of 40 kDa upon Superose 6 gel-filtration chromatography. No methylation activity towards N-acetyl-S-trans,trans-farnesylcysteine (AFC), a good substrate for C-terminal carboxyl methyltransferases, was associated with either peaks. In contrast, the increase in methylation induced by these proteins was strongly inhibited by AFC, suggesting that the methylation induced by these factors occurred on C-terminal isoprenylated cysteine residues. Both partially purified proteins competitively inhibited the methylation of AFC by the membrane-associated enzymes, suggesting that they may represent substrates for the methyltransferases. Immunoblotting of these partially purified soluble substrates with a rabbit polyclonal antibody directed against the small G-protein CDC42 showed the presence of this protein in peak I but not in peak II. Taken together, these results suggest the presence in a soluble fraction from the kidney of distinct methyl-accepting proteins, one of these being tentatively identified as the small G-protein CDC42.

Animals↗
PubMed1975

Effect of glucose on the utilization of palmitate 1 14C by rat kidney cortex slices.

The authors studied the effect of glucose on the uptake and utilization of palmitate 1 14C by rat kidney cortex slices. They found that its inhibitory effect on free fatty acid (FFA) uptake was caused by inhibition of the incorporation of 1 14C-labelled palmitate into the total lipids and FFA and by reduced oxidation to 14CO2. Glucose has a regulative function in the utilization of FFA by the kidneys.

Animals↗
PubMed1979

Studies on the isolation and properties of renin granules from the rat kidney cortex.

The present study was undertaken to isolate and investigate some physicochemical properties of renin granules from the rat kidney cortex. Two preparations of subcellular organelles were used: a primary-granule fraction, which allowed the properties of lysosomes to be compared simultaneously with those of renin granules, and a semi-purified preparation of the latter. The specific activity of renin in the primary-granule preparations was about 4-fold higher than in the original homogenate; that of the semi-purified renin-granule preparation was about 18-fold higher than in the homogenate, and consisted mainly of electron-dense granules but some mitochondria were also observed. Renin and acid phosphatase release from the primary-granule preparation was increased by lowering osmolality, by a low-molecular-weight solute (glucose) and by Triton X-100 or digitonin. Enzyme release was decreased by lowering the incubation temperature (4 degrees C) or the presence of CaCl2. Renin release from the partially purified granule preparation was not affected by cyclic AMP, cyclic GMP and ATP.

Acid Phosphatase↗
PubMed1980

Parathyroid hormone acutely increases polyphosphoinositides of the rabbit kidney cortex by a cycloheximide-sensitive process.

Parathyroid hormone(PTH) rapidly increases the concentrations of diphosphoinositide and triphosphoinositide in rabbit kidney cortex. Cycloheximide pretreatment abolishes these effects of PTH. These findings are similar to those reported for adrenocorticotropin and cyclic AMP action in the adrenal cortex, and suggest a common mechanism. Cycloheximide-sensitive effects of PTH, e.g., phosphaturia, may require polyphosphoinositides and/or other phospholipids.

Animals↗
PubMed1996

Kinetic characterization of zinc binding to brush border membranes from rat kidney cortex: interaction with cadmium.

Extravesicular and intravesicular zinc bindings were evaluated in brush border membrane vesicles isolated from rat kidney cortex. The process was found to be time-, temperature- and substrate concentration-dependent and displayed saturability. Zn2+ influx measurements revealed a progressive uptake and massive accumulation at equilibrium which was 50 times higher than the amount that could have been accommodated by the intravesicular space calculated from the equilibrium uptake of D-glucose. Initial (5 s) and equilibrium uptakes (2 h) were found not to be osmotically sensitive as modified by adding mannitol to the medium. It was concluded from these results that the uptake involved massive binding of the Zn2+ to the brush border membranes components. The ionophore A23187 enhanced the rates of uptake and efflux of Zn2+ without affecting equilibrium values, suggesting binding of Zn2+ to interior sites of the membranes. Zn2+ flux measurements led to the conclusion that two vesicular pools of Zn2+ bindings existed: a small external pool, accessible to cation chelator (EGTA) or competitive cation cadmium and large intravesicular pool. Accumulated 65Zn was quickly removed from its internal sites only after the membrane had been permeabilized by the cation ionophore A23187 in association with exchangeable ions like zinc and cadmium. Scatchard plot analysis revealed two distinct types of extravesicular binding sites. High affinity extravesicular zinc binding sites reached saturation at 1.6 mM zinc, had a Kd of 137 microM and the number of binding sites were 12 nmol/mg protein. Low affinity extravesicular zinc binding sites could not be saturated under experimental conditions up to 3.2 mM zinc. It had a Kd of 526 microM and the number of binding sites 28 nmol/mg protein. Interestingly intravesicular binding of zinc revealed only one type of high affinity binding sites (Kd of 104 microM and number of maximal binding sites 400 nmol/mg protein). Furthermore, kinetic analysis of inhibitory effect of Cd2+ on extravesicular zinc bindings showed an increase in Kd of both types of binding sites but there was no significant change in number of maximal binding sites. Extravesicular zinc binding was temperature-sensitive. Arrhenius plot showed the break point at 30 degrees C. The apparent energies of activation were 13.36 Kcal/mol and 3.1 Kcal/mol below and above the break points respectively. The inhibitory effect of sulfhydryl blocking agents on extravesicular zinc binding suggest the involvement of -SH groups in zinc translocation. An increase in initial zinc uptake was observed in the presence of outwardly directed proton gradient. Intravesicular pool of 65Zn was displaced by unlabelled 2 mM Zn2+ or 2 mM Cd2+ but not by calcium present in the bathing medium. It is inferred that intravesicular binding sites have a high affinity and are specific for zinc. It is concluded from the present study that in the first instance the binding of zinc to the exofacial zinc binding component and concomitantly its translocation across the membrane, and subsequently massive binding of zinc to interior sites of brush border membranes occurs.

Animals↗
PubMed1969

Acceleration of gluconeogenesis from propionate by Dl-carnitine in the rat kidney cortex.

1. The rate of gluconeogenesis from propionate in rat kidney-cortex slices was stimulated up to 3.5-fold by dl-carnitine and by bicarbonate, and was inhibited by inorganic phosphate or high concentrations of propionate (above 3mm). 2. The stimulatory effect of carnitine was dependent on the bicarbonate concentration and could be replaced at low propionate concentration by addition of 25mm-bicarbonate-carbon dioxide buffer. At low bicarbonate concentration the carnitine concentration can be rate-limiting. 3. All observations are in accordance with the view that the action of carnitine is in principle the same as that established for other fatty acids in other tissues, namely that carnitine promotes the appearance of propionyl-CoA within the mitochondrion by acting as a carrier. 4. The accelerating effects of carnitine and bicarbonate and the inhibitory effect of phosphate can be explained on the basis of the known properties of key enzymes of propionate metabolism, i.e. the reversibility of the reactions leading to the formation of methylmalonyl-CoA from propionyl-CoA. 5. 5mm-Propionate caused a five- to ten-fold fall in the free CoA content of the tissue. This fall can account for the inhibition of respiration and gluconeogenesis caused by high propionate concentration. 6. Relatively large quantities of propionyl-l-carnitine (15% of the propionate removed) were formed when dl-carnitine was present; thus the ;activation' of propionate proceeded at a faster rate than the carboxylation of propionyl-CoA. The metabolism of added propionyl-l-carnitine was accompanied by glucose synthesis. 7. The appearance of radioactivity from [2-(14)C]propionate in both glucose and carbon dioxide was as expected on account of the randomization of C-2 and C-3 of propionate, i.e. the formation of succinate as an intermediate. 8. The maximum rate of glucose synthesis from propionate (93.3+/-3.3mumoles/g. dry wt./hr.) was not affected by dietary changes aimed at varying the rate of caecal volatile fatty acid formation in the rat. 9. Inhibition of gluconeogenesis by high propionate concentration was not found in those species where the rate of caecal or ruminal propionate production is high under normal conditions (rabbit, sheep and cow).

Animals↗
PubMed1985

Uptake of proline by brushborder vesicles isolated from human kidney cortex.

Proline transport into renal brushborder membrane vesicles isolated from human kidney is mediated by two uptake systems. The high-affinity system is stimulated by a Na gradient and appears to be shared with glycine while the low-affinity system is not. Uptake curves of low concentrations of proline exhibit a Na-gradient-dependent overshoot indicative of electrogenic transport. The proline transport systems observed in isolated human renal brushborder membrane vesicles appear to have characteristics similar to those in rat kidney membranes.

Alanine↗
PubMed1989

Evidence for the occurrence of an alkaline proteinase in kidney cortex lysosomes.

A novel alkaline endoproteinase optimally active at pH 8.5 has been detected in highly pure preparations of buffalo kidney cortex lysosomes. The enzyme has been partially purified (90-fold) by solubilization with octylglucoside, acid precipitation and chromatography over DEAE sephacel and sepharose 6B. The alkaline proteinase, resistant to known inhibitors of lysosomal cathepsins is inhibited by soyabean trypsin inhibitor and phenyl methyl sulphonyl fluoride indicating that the enzyme is a serine proteinase.

Animals↗
PubMed1987

Association of isolated bovine kidney cortex peroxisomes with endoplasmic reticulum.

Close lateral membrane associations of peroxisomes with endoplasmic reticulum are a common feature in bovine kidney cortex epithelial cells. Isolated highly purified peroxisome preparations from this tissue showed a remarkable and persistent copurification of peroxisomal marker enzymes with small amounts (5%) of the microsomal reference enzymes esterase and glucose-6-phosphatase. Contamination with mitochondrial and lysosomal markers was negligible. Ultrastructural examination of such preparations revealed a peculiar association of vesicles or short tubular segments with the peroxisomal membrane. Short electron dense crossbridges seemed to maintain their structural association. The cytochemical localization of glucose-6-phosphatase in peroxisome-associated membrane structures confirmed their derivation from endoplasmic reticulum. The metabolic significance of such structural peroxisome-endoplasmic reticulum associations is discussed.

Animals↗
PubMed2006

Thermotropic lipid phase transition and the behavior of hydrolytic enzymes in the kidney cortex brush border membrane.

Functional interactions of lipids and proteins were examined in brush-border membranes isolated from the kidney cortex by studying the temperature dependence of the hydrolytic enzyme activities. A close relationship was observed for the membrane proteins and the thermotropic lipid phase transitions. Three lines of evidences were provided for such dependence: a) Arrhenius relationship of the membrane-bound enzyme activities, and the effect of temperature in native and partially delipidated membranes, b) differential scanning calorimetric study of the membrane lipid phase transitions in the native and delipidated membranes, multilamellar vesicles prepared from the membrane extracted lipids, and in vesicles from dimyristoyl phosphatidylcholine, and c) the excimer (dimer)-formation studies of the membrane extrinsic fluorescent probe, pyrene, and the resultant membrane microviscosity. The brush-border membranes were partially delipidated with BuOH and 2,2,2-trifluoroethanol. The functional interactions of the delipidated membranes, which were greatly lost on lipid removal, were largely restored by the addition of exogenous lipids in the reconstitution process, which indicate the critical dependence of the membrane integral proteins on the neighboring lipid molecules in the bulk lipid phase.

Animals↗
PubMed1994

Tyrosine protein phosphorylation in plasma membranes of rat kidney cortex.

The endogenous tyrosine protein kinase activity (TPKA) associated with brush-border (BBM) and basolateral (BLM) membranes of rat kidney cortex was studied with an anti-phosphotyrosine monoclonal antibody (PY20). Distinct major phosphotyrosine-containing proteins were associated with BBM (50, 54, and 120 kDa) and BLM (37, 90, 130, and 170 kDa). For both plasma membranes, tyrosine phosphorylation leveled off after 10 min of incubation. Endogenous phosphotyrosine-specific protein phosphatases (PT-Pases) were active in both membranes, since the presence of sodium vanadate or ammonium molybdate, which are inhibitors of PTPases, was essential to detect endogenous phosphorylation. Substrates and/or tyrosine protein kinases (TPKs) seem to be differently distributed in these plasma membranes, since phosphorylation of endogenous substrates in BLM and BBM was differently sensitive to competitive inhibitors of TPKs. Moreover, insulin- and insulin-like growth factor I-stimulated tyrosine phosphorylation of a 90-kDa substrate was only observed in solubilized BLM proteins. However, similar p60v-src-related TPKs appear to be present in the BBM and BLM, since an antibody raised against p60v-src recognized proteins of 52, 58, and 75 kDa by immunoblotting and could immunoprecipitate the TPKs associated with both plasma membranes. These data provide evidence that the endogenous tyrosine protein phosphorylation observed in the BLM is catalyzed by nonreceptor TPKs as well as receptor TPKs, whereas that observed in the BBM is exclusively due to nonreceptor TPKs.

Adenosine Triphosphate↗
PubMed1978

[Effect of sodium fluoride on the metabolism of the rat kidney cortex and medulla].

Tissue sections of cortex and outer and inner medulla of rat kidneys were examined in the Warburg apparatus with and without addition of NaF. It was shown that the O2 consumption was not significantly reduced in the presence of 0.05 mM F (=0.95 ppm F!) or smaller amounts. The respiratory quotient was not changed by NaF. Lactate formation in sections from the inner medulla was reduced to the same degree as O2 consumption. Maximal concentrations of plasma fluoride which are met in doses of fluoride used for the prophylaxis of caries, do not impair renal metabolism.

Animals↗
PubMed1976

Plasma membrane changes in freeze-fractured rat kidney cortex following renal ischemia.

Ischemia was produced in the inner cortex of the rat kidney by clamping the pedicle (artery, vein, and ureter) and severing collateral connections. After 30 minutes of ischemia, a slight aggregation of membrane-associated particles was observed in the freeze-fractured plasma membranes. The aggregation was progressive after 60 and 120 minutes of ischemia. These changes were reversible after 15 and 240 minutes of reflow of blood following 30 or 60 minutes of ischemia. The changes were irreversible after 120 minutes of ischemia. The cells were vacuolated after ischemic periods of 30 minutes or longer and after 120 minutes of ischemia the tissue was severely damaged and aggregation of membrane-associated particles was evident in the vacuolar membranes. No changes in the tissue or plasma membrane were observed after 5 or 20 minutes of ischemia.

Animals↗
PubMed1993

Regulation of rat-kidney cortex fructose-1,6-bisphosphatase activity. I. Effects of fructose-2,6-bisphosphate and divalent cations.

1. The native rat-kidney cortex Fructose-1,6-BPase is differentially regulated by Mg2+ and Mn2+. 2. Mg2+ binding to the enzyme is hyperbolic and large concentrations of the cation are non-inhibitory. 3. Mn2+ produces a 10-fold rise in Vmax higher than Mg2+. [Mn2+]0.5 is much larger than [Mg2+]0.5. At elevated [Mn2+] inhibition is observed. 4. Mg2+ and Mn2+ produce antagonistic effects on the inhibition of the enzyme by high substrate. 5. Fru-2,6-P2 inhibits the enzyme by rising the S0.5 and favouring a sigmoidal kinetics. 6. The inhibition by Fru-2,6-P2 is released by Mg2+ and more powerfully by Mn2+ increasing the I0.5.

Animals↗
PubMed1982

Effect of potassium on p-aminohippurate transport in rat kidney cortex slices.

The effects of medium K+ concentration on the tissue uptake of p-aminohippurate (PAH) were investigated in rat kidney cortex slices. K+ concentration in the incubation medium was changed in the absence of Na+. Increase in K+ concentration up to 145 mM revealed an augmenting effect on PAH uptake when tissue water content was controlled at about 72% by elevating medium osmolarity with mannitol. The K+-induced enhancement of PAH uptake was almost completely abolished by the simultaneous presence of extremely high concentration of hippurate. Anoxia reduced this augmenting effect. Pyruvate added to the medium scarcely affected this augmenting effect. The uptake rate during the initial 10-min incubation increased linearly in proportion to the increase in log [K]o/[K]i. The results suggest that high medium K+ concentration stimulates PAH transport by a carrier-mediated process which is dependent on oxidative metabolism. However, the mode of action of K+ on PAH uptake seems to be different from that of Na+. It seems likely that K+ exerts its effect on PAH transport by the alteration of the peritubular membrane potential.

Aminohippuric Acids↗
PubMed1987

Inhibitory effect of gentamicin on gluconeogenesis from pyruvate, propionate, and lactate in isolated rabbit kidney-cortex tubules.

The effect of gentamicin on glucose production in isolated rabbit renal tubules was studied with lactate, propionate, malate, 2-oxoglutarate, and succinate as substrates. This antibiotic at 5 mM concentration inhibited gluconeogenesis from lactate by about 60% and that from either pyruvate or propionate by about 30%. In contrast, it did not alter the rate of glucose formation from other substrates studied. The rate of gluconeogenesis was higher at 1 mM propionate than at increasing concentrations of this substrate and was stimulated in the presence of 1 mM carnitine. However, the addition of carnitine did not affect the degree of inhibition of glucose formation by gentamicin. Since the mitochondrial free coenzyme A level was significantly lower in the presence of 10 than 1 mM propionate and increased on the addition of carnitine to the reaction medium, the inhibitory effect of propionate concentrations above 1 mM on gluconeogenesis in rabbit renal tubules may be due to a depletion of the free mitochondrial coenzyme A level, resulting in an inhibition of the mitochondrial coenzyme A-dependent reactions. In intact rabbit kidney cortex mitochondria incubated in State 4 as well as in Triton X-100-treated mitochondria, 5 mM gentamicin inhibited by about 30-40% the incorporation of 14CO2 into both pyruvate and propionate. The results indicate that the inhibitory effect of gentamicin on glucose formation in isolated kidney tubules incubated with lactate, pyruvate, or propionate is likely due to a decrease of the rate of carboxylation reactions.

Animals↗
PubMed1993

Phosphorylation and activation of protamine kinase by two forms of a myelin basic protein kinase from extracts of bovine kidney cortex.

Two myelin basic protein kinases designated MBPK-1 and MBPK-2 were purified to apparent homogeneity from extracts of bovine kidney cortex. The purified preparations exhibited an apparent M(r) approximately 40,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and approximately 42,000 (MBPK-1) and 45,000 (MBPK-2) by gel permeation chromatography. Up to 0.4 and 1.8 mol of phosphoryl groups were incorporated per mol of MBPK-1 and MBPK-2, respectively, on threonines following incubation with ATP. Autophosphorylation, incubation with protein phosphatase 2A2 (PP2A2), CD45, or T-cell protein tyrosine phosphatase did not affect MBPK-1 activity. Autophosphorylation increased by about 3-fold MBPK-2 activity. This autophosphorylation and activation was reversed by PP2A2 but not by CD45 or T-cell protein tyrosine phosphatase. MBPK-1 and MBPK-2 displayed a positive reaction with an antibody to mitogen-activated protein kinase. Purified preparations of protamine kinase were activated by about 1.5-6-fold and, after inactivation with PP2A2, were reactivated by about 30% by MBPK-1 and MBPK-2. Activation and reactivation correlated with the incorporation, respectively, of 0.1-0.5 and 0.5 mol of phosphoryl groups/mol of the protamine kinase on serines. The results show that MBPK-1 and MBPK-2 are protamine kinase-activating kinases and suggest that MBPK-1 and MBPK-2 may be related to mitogen-activated protein kinase.

Amino Acid Sequence↗