Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

L6 myoblasts spontaneously undergo differentiation and cell fusion into myotubes. These cells express both GLUT1 and GLUT4 glucose transporters, but their expression varies during myogenesis. We now report that the subcellular distribution and the protein processing by glycosylation of both glucose transporter isoforms also change during myogenesis. Crude plasma membrane and light microsome fractions were isolated from either myoblasts or myotubes and characterized by the presence of two functional proteins, the Na+/K(+)-ATPase and the dihydropyridine receptor (DHPR). Immunoreactive alpha 1 subunit of the Na+/K(+)-ATPase was faint in the crude plasma membrane fraction from myoblasts, but abundant in both membrane fractions from myotubes. In contrast, the alpha 1 subunit of the DHPR, which is expressed only in differentiated muscle, was detected in crude plasma membrane from myotubes but not from myoblasts. Therefore, crude plasma membrane fractions from myoblasts and myotubes contain cell surface markers, and the composition of these membranes appears to be developmentally regulated during myogenesis. GLUT1 protein was more abundant in the crude plasma membrane relative to the light microsome fraction prepared from either myoblasts or myotubes. The molecular size in sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the GLUT1 transporters in myotubes was smaller than that in myoblasts (Mr 47,000 and 53,000, respectively). GLUT4 protein (Mr 48,000) was barely detectable in the crude plasma membrane fraction and was almost absent in the light microsome fraction prepared from myoblasts. However, GLUT4 protein was abundant in myotubes and was predominantly located in the light microsome fraction. Treatment with endoglycosidase F reduced the molecular size of the transporters in all fractions to Mr 46,000 for GLUT1 and Mr 47,000 for GLUT4 proteins. In myotubes, acute insulin treatment increased the crude plasma membrane content of GLUT1 marginally and of GLUT4 markedly, with a concomitant decrease in the light microsomal fraction. These results indicate that: (a) the subcellular distribution of glucose transporters is regulated during myogenesis, GLUT4 being preferentially sorted to intracellular membranes; (b) both GLUT1 and GLUT4 transporters are processed by N-linked glycosylation to form the mature transporters in the course of myogenesis; and (c) insulin causes modest recruitment of GLUT1 transporters and marked recruitment of GLUT4 transporters, from light microsomes to plasma membranes in L6 myotubes.
...
PMID:Development regulation of the subcellular distribution and glycosylation of GLUT1 and GLUT4 glucose transporters during myogenesis of L6 muscle cells. 131 24

Unlike glucose transport, where translocation of the insulin-responsive glucose transporter (GLUT4) from an intracellular compartment to the plasma membrane is the principal mechanism underlying insulin stimulation, no consensus exists presently for the mechanism by which insulin activates the Na+/K(+)-ATPase. We have investigated (i) the subunit isoforms expressed and (ii) the effect of insulin on the subcellular distribution of the alpha beta isoforms of the Na+/K(+)-ATPase in plasma membranes (PM) and internal membranes (IM) from rat skeletal muscle. Western blot analysis, using isoform-specific antibodies to the various subunits of the Na+/K(+)-ATPase, revealed that skeletal muscle PM contains the alpha 1 and alpha 2 catalytic subunits and the beta 1 and beta 2 subunits of the Na+ pump. Skeletal muscle IM were enriched in alpha 2, beta 1, and beta 2; alpha 1 was barely detectable in this fraction. After insulin treatment, alpha 2 content in the PM increased, with a parallel decrease in its abundance in the IM pool; insulin did not have any effect on alpha 1 isoform amount or subcellular distribution. The beta 1 subunit, but not beta 2, was also elevated in the PM after insulin treatment, but this increase originated from a sucrose gradient fraction different from that of the alpha 2 subunit. Our findings suggest that insulin induces an isoform-specific translocation of Na+ pump subunits from different intracellular sources to the PM and that the hormone-responsive enzyme in rat skeletal muscle is an alpha 2:beta 1 dimer.
...
PMID:Insulin induces translocation of the alpha 2 and beta 1 subunits of the Na+/K(+)-ATPase from intracellular compartments to the plasma membrane in mammalian skeletal muscle. 131 81

A rat kidney- and intestine-specific cDNA (D2) that induces high-affinity, Na(+)-independent uptake of cystine and dibasic and neutral amino acids into cRNA-injected Xenopus oocytes was recently isolated by expression cloning in our laboratory (R. G. Wells and M. A. Hediger. Proc. Natl. Acad. Sci. USA 89: 5596-5600, 1992). At present it is not known whether the D2-encoded protein functions as a transporter or as a transporter activator. To gain more insight into the role of D2 in renal amino acid transport, we studied the site of its expression in the kidney. This was determined by Northern blot analysis and by using a combination of in situ hybridization and immunocytochemistry with antibodies that recognize specific proximal tubule segments. D2 antisense RNA hybridized to the same tubular segments that were strongly positive for anti-ecto-adenosinetriphosphatase but negative for carbonic anhydrase type IV and the facilitated glucose transporter GLUT2. We conclude that D2 mRNA is strongly expressed in the rat kidney proximal tubule S3 segment, although there is weak hybridization to the S1 and S2 segments. The signal is absent in all other parts of the kidney. The S3 specific expression of D2 mRNA coincides with the site of high-affinity transport of cystine and other amino acids, consistent with the proposed involvement of D2 in these processes.
...
PMID:Expression of mRNA (D2) encoding a protein involved in amino acid transport in S3 proximal tubule. 148 85

D-Glucose protectable cytochalasin B (CB) binding to subcellular membrane fractions was used to determine glucose transporter number in red (quadriceps-gastrocnemius-soleus) and white (quadriceps-gastrocnemius) rat muscle. CB binding was twofold higher in isolated plasma membranes of red than of white muscle. In contrast, the number of transporters in an isolated insulin-sensitive intracellular membrane organelle was similar in the two muscle groups. Immunoblotting and immunofluorescence microscopy with anti-GLUT4 and anti-GLUT1 antibodies indicated that both GLUT1 and GLUT4 transporter isoforms account for the higher abundance of CB binding sites in plasma membranes of red than of white muscle. Immunofluorescence localized GLUT4 to both the surface and the interior of the muscle cell and demonstrated that type I (slow twitch oxidative) and type IIa (fast twitch oxidative-glycolytic) fibers are enriched in GLUT4 protein compared with type IIb (fast twitch glycolytic) fibers. In contrast, GLUT1 reactivity was restricted to the surface of the muscle cell and was also highly enriched in the perineurial sheaths of peripheral nerves and the capsules of muscle spindles present in both red and white muscles. Insulin caused a twofold increase in CB binding in isolated plasma membranes of red or white muscles with a corresponding 40-50% decrease in CB binding in isolated intracellular membranes. These changes in CB binding were paralleled by similar changes in the membrane distribution of the GLUT4 glucose transporter isoform and in glucose transport activity measured after insulin perfusion of hindquarter muscles. In contrast, insulin did not change the distribution of either GLUT1 glucose transporters or Na(+)-K(+)-ATPase alpha 1-subunits. The molar ratio of GLUT4 to GLUT1 in red and white muscle plasma membranes was found to be 4:1 in the basal state and 7:1 in the insulin-stimulated state. These results indicate that red muscle contains a higher amount of GLUT1 and GLUT4 transporters at the plasma membrane than white muscle in the basal and insulin-stimulated states but that GLUT4 translocation does not differ between muscle types. In addition, GLUT4 expression correlates with the metabolic nature (oxidative vs. glycolytic) of skeletal muscle fibers, rather than with their contractile properties (slow twitch vs. fast twitch).
...
PMID:Abundance, localization, and insulin-induced translocation of glucose transporters in red and white muscle. 151 90

In obesity, impaired glucose tolerance (IGT), non-insulin-dependent diabetes mellitus (NIDDM), and gestational diabetes mellitus (GDM), defects in glucose transport system activity, contribute to insulin resistance in target tissues. In adipocytes from obese and NIDDM patients, we found that pretranslational suppression of the insulin-responsive GLUT4 glucose transporter isoform is a major cause of cellular insulin resistance; however, whether this process is operative in skeletal muscle is not clear. To address this issue, we performed percutaneous biopsies of the vastus lateralis in lean and obese control subjects and in obese patients with IGT and NIDDM and open biopsies of the rectus abdominis at cesarian section in lean and obese gravidas and gravidas with GDM. GLUT4 was measured in total postnuclear membrane fractions from both muscles by immunoblot analyses. The maximally insulin-stimulated rate of in vivo glucose disposal, assessed with euglycemic glucose clamps, decreased 26% in obesity and 74% in NIDDM, reflecting diminished glucose uptake by muscle. However, in vastus lateralis, relative amounts of GLUT4 per milligram membrane protein were similar (NS) among lean (1.0 +/- 0.2) and obese (1.5 +/- 0.3) subjects and patients with IGT (1.4 +/- 0.2) and NIDDM (1.2 +/- 0.2). GLUT4 content was also unchanged when levels were normalized per wet weight, per total protein, and per DNA as an index of cell number. Levels of GLUT4 mRNA were similarly not affected by obesity, IGT, or NIDDM whether normalized per RNA or for the amount of an unrelated constitutive mRNA species. Because muscle fibers (types I and II) exhibit different capacities for insulin-mediated glucose uptake, we tested whether a change in fiber composition could cause insulin resistance without altering overall levels of GLUT4. However, we found that quantities of fiber-specific isoenzymes (phopholamban and types I and II Ca(2+)-ATPase) were similar in all subject groups. In rectus abdominis, GLUT4 content was similar in the lean, obese, and GDM gravidas whether normalized per milligram membrane protein (relative levels were 1.0 +/- 0.2, 1.3 +/- 0.1, and 1.0 +/- 0.2, respectively) or per wet weight, total protein, and DNA. We conclude that in human disease states characterized by insulin resistance, i.e., obesity, IGT, NIDDM, and GDM, GLUT4 gene expression is normal in vastus lateralis or rectus abdominis. To the extent that these muscles are representative of total muscle mass, insulin resistance in skeletal muscle may involve impaired GLUT4 function or translocation and not transporter depletion as observed in adipose tissue.
...
PMID:Gene expression of GLUT4 in skeletal muscle from insulin-resistant patients with obesity, IGT, GDM, and NIDDM. 153 55

The (Na+,K+) ATPase in plasma membranes isolated from rat adipocytes is insensitive to insulin (Lytton J., Lin, J.C., and Guidotti, G. (1985) J. Biol. Chem. 260, 1177-1184). For this reason, the characteristics of the (Na+,K+) pump in adipocyte ghosts, prepared by hypotonic lysis of adipocytes (Rodbell, M. (1967) J. Biol. Chem. 242, 5744-5750), were studied. Herein it is demonstrated that the (Na+,K+) pump in ghosts is identical to that described in isolated plasma membranes, sharing the following characteristics: 1) the Ki values for ouabain are 1.3 x 10(-7) M and 4.5 x 10(-5) M for the alpha 2 and alpha 1 isozymes, respectively; 2) the K0.5 values for sodium are 11.4 +/- 1.6 and 7.2 +/- 3.8 mM for the alpha 2 and alpha 1 isozymes, respectively; 3) both forms of the (Na+,K+) pump are insensitive to insulin stimulation, presumably because the activities are already maximal. The ghosts are not in an insulin-stimulated state because the activity of the glucose transporter is not increased as it is in ghosts prepared from insulin-treated cells. In addition, presented evidence demonstrates that ghost internal sodium concentration, [Na+]i, is very sensitive to changes in the activity of the (Na+,K+) pump. If the [Na+]i, of adipocytes is also very sensitive to the activity of the (Na+,K+) pump, the mechanism of insulin stimulation of the adipocyte (Na+,K+) pump requires reexamination.
...
PMID:Characterization of the adipocyte ghost (Na+,K+) pump. Insights into the insulin regulation of the adipocyte (Na+,K+) pump. 165 21

Glucose transport in the bloodstream form of the protozoan parasite Trypanosoma brucei was characterized by enzymatically measuring the D-glucose uptake. Uptake kinetics showed a concentration-dependent saturable process, typical for a carrier-mediated transport system, with an apparent Km = 0.49 +/- 0.14 mM and Vmax = 252 +/- 43 nmol.min-1.mg cell protein-1 (equal to 2.25 x 10(8) trypanosomes). The specificity of glucose transport was investigated by inhibitor studies. Glucose uptake was shown to be sodium independent; neither the Na+/K(+)-ATPase inhibitor ouabain (1 mM) nor the ionophor monensin (1 microM) inhibited uptake. Transport was also unaffected by the H(+)-ATPase inhibitor N,N'-dicyclohexylcarbodiimide (DCCD; 20 microM) and the uncoupler carbonylcyanide-4-(trifluoromethoxy)phenylhydrazone (FCCP; 1 microM). However, highly significant inhibition was obtained with both phloretin (82% at 0.13 mM; Ki = 64 microM) and cytochalasin B (77% at 0.3 mM; Ki = 0.44 mM), and partial inhibition with phlorizin (14% at 0.5 mM; Ki = 3.0 mM). In each case, inhibition was noncompetitive, partially reversible (45%) for phloretin and completely reversible for cytochalasin B and phlorizin. Measurement of the temperature-dependent glucose uptake between 25 degrees C and 37 degrees C resulted in a temperature quotient of Q10 = 1.97 +/- 0.02 and an activation energy of Ea = 52.12 +/- 1.00 kJ/mol for glucose uptake. We conclude that glucose uptake in T. brucei bloodstream forms occurs via a facilitated diffusion system, clearly distinguished from the human erythrocyte-type glucose transporter with about a 10-fold higher affinity for glucose and about a 1000-fold decreased sensitivity to the inhibitor cytochalasin B.
...
PMID:Specificity of glucose transport in Trypanosoma brucei. Effective inhibition by phloretin and cytochalasin B. 193 76

The levels of mRNAs encoding the alpha 1 chain of collagen IV and the B1 chain of laminin were assayed in the lenses and retinas of long-term (28-week) diabetic and galactosaemic rats in order to gain some insight into the effects on basement membrane (BM) synthesis in these tissues. mRNAs coding for beta-actin, glucose transporter protein and the alpha 2 catalytic subunit of Na+,K(+)-ATPase were also assayed to determine whether any effects on BM-coding mRNA levels were specific. Long-term diabetes had no significant effect on the levels of alpha 1 (IV) collagen mRNA but caused a significant reduction in the laminin B1 message in the lens. In the same samples, the level of the glucose transporter protein mRNA was found to be elevated significantly in the diabetic tissue, whereas the mRNAsen coding beta-actin and alpha 2 Na+,K(+)-ATPase were unaffected in comparison with age-matched controls. Long-term galactosaemia resulted in significant increases in the levels of all mRNAs assayed when expressed per micrograms total RNA used for each analysis. However, this effect appeared to be due to a specific loss of ribosomal RNA from these severely cataractous lenses. When related to the beta-actin mRNA internal control, the levels of mRNA in the galactosaemic lenses were very similar to that found in the diabetics. Laminin B1 mRNA levels were decreased significantly.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Effects of long-term diabetes and galactosaemia upon lens and retinal mRNA levels in the rat. 216 48

The transmembrane segments predicted for the Neurospora H-ATPase are laid out diagrammatically in Figure 10. Although the eight segments have arbitrarily been compressed into rectangles of the same size, they range in length from 20 residues (II) to 30 residues (IV and VI), so the corresponding helices must vary in length as well. Notable features of the model include the charged residues located just outside the plane of the membrane, with a clear excess of negative charges (5-, 1+) at the extracellular surface and a slight excess of positive charges (4+, 3-) at the cytoplasmic surface. There are also a conspicuous number of bulky residues (tryptophan, phenylalanine, and tyrosine) just inside the plane of the membrane. Within the bilayer, most of the helices are noticeably amphipathic, consistent with the expectation that at least some of them stack together to form a channel-like structure with a hydrophobic surface and a hydrophilic core. The charged residues predicted to lie within the membrane are listed in Table 2, which is a summary of data from eight of the P-type ATPases; the S. cerevisiae and S. pombe enzymes have not been included because they are nearly identical in this respect to the Neurospora enzyme. Interestingly, all of the ATPases have more membrane-embedded negative charges (5 to 8) than positive ones (0 to 4), a pattern that may be connected with their role as cation transporters. Certainly, other unrelated transport proteins have a rather different pattern of positive and negative charges: for example, the mammalian glucose transporter (1+, 2-), Na-glucose transporter (3+, 3-), and the E. coli lac permease (11+, 7-). The actual positioning of the negative charges in the P-type ATPases does not make it easy to single out the functionally important ones, however. The glutamyl residue in segment I is present in the fungal, plant, and Leishmania H-ATPases but not in the gastric H,K-ATPase. The same is true for the aspartate in segment II, except that it also appears in the muscle and brain Ca-ATPases. A glutamate is found at one end of segment III in the E. coli and fungal enzymes and at the other end in Arabidopsis; in segment IV, another glutamate appears in a well-conserved region in the Leishmania and mammalian enzymes but not in the bacterial, fungal, or plant ones.(ABSTRACT TRUNCATED AT 400 WORDS)
...
PMID:Transmembrane segments of the P-type cation-transporting ATPases. A comparative study. 256 19

The time course of insulin activation of sodium and potassium ion activated adenosinetriphosphatase [(Na+,K+)ATPase] was studied in the rat adipocyte and was compared to activation of the glucose transporter. Under conditions in which the binding of insulin to its cell surface receptor was not rate limiting, a distinct time lag was apparent between insulin addition and stimulation of transport activity. At 37 degrees C, 40-50 s elapsed before an increase in Rb+ uptake [a measure of (Na+,K+)ATPase transport activity] or 2-deoxyglucose uptake could be observed. This lag time increased in an identical manner for both transport processes as the temperature was lowered to 23 degrees C. Addition of the insulinomimetic agent hydrogen peroxide also produced a lag time similar to that for insulin before activation of Rb+ and 2-deoxyglucose uptakes was detected. These data provide the first evidence of a discrete time lag involved during stimulation of the adipocyte (Na+,K+)ATPase. A model for the molecular mechanism of insulin activation of (Na+,K+)ATPase is presented that incorporates these results into the hypothesis of insulin mediated "translocation" of glucose transporters to the plasma membrane.
...
PMID:Insulin activation of (Na+,K+)-adenosinetriphosphatase exhibits a temperature-dependent lag time. Comparison to activation of the glucose transporter. 630 47


1 2 3 4 5 6 7 8 9 10 Next >>

---