Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.1.2.13 (aldolase)
 3,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The masses of inositol phosphates have been determined in isolated skeletal muscles from Xenopus laevis (sartorius, tibialis anterior and iliofibularis) and rat (gastrocnemius and soleus) which were quick-frozen in the resting state and at different stages of an isometric (Xenopus) or isotonic (rat) tetanus. The isomeric spectrum of inositol phosphates detected was similar to that in other tissues and cell types. The total sarcoplasmic concentrations of the isomers Ins-(1,4,5,6)P4/Ins(3,4,5,6)P4 (0.2-0.9 microM), Ins(1,3,4,6)P4 (not detectable), Ins(1,3,4,5,6)P5 (about 1 microM) and InsP6 (3.2-4.6 microM) were lower than in other cell types. Variations in these concentrations were due to the muscle type rather than to the donor species. The putative second messenger Ins(1,4,5)P3, as well as its dephosphorylation product Ins(1,4)P2, were present at surprisingly high total myoplasmic resting concentrations, ranging from 1.2 to 2.5 microM and 3.5 to 6.9 microM respectively. Upon tetanic stimulation these two inositol phosphates in particular exhibited significantly increased total sarcoplasmic concentrations, up to 4.2 microM and 11.3 microM respectively, with a time scale of seconds. From the initial rate of increase in the total sarcoplasmic concentrations of Ins(1,4,5)P3 and its rapidly formed metabolic products, a minimal phosphoinositidase C (PIC) activity in tetanically activated Xenopus skeletal muscle of about 1.7-2.6 microM/s can be estimated. This PIC activity observed in vivo seems to be far too low to account for a functional role for Ins(1,4,5)P3 as a chemical transmitter in the fast excitation-contraction coupling (ECC) process in skeletal muscle. The presence of Ins(1,3,4,5)P4 in all muscle types is indicative of a Ca(2+)-activated Ins(1,4,5)P3 3-kinase activity. The rapid transient increases in Ins(1,3,4)P3 and Ins(1,3)P2 in isometrically contracting Xenopus muscles suggest that corresponding Ins(1,3,4,5)P4 phosphatases are operating in skeletal muscle as well. In all muscles investigated except rat soleus, the fructose 1,6-bisphosphate [Fru(1,6)P2] concentration increased substantially during a tetanus, up to about 2 mM. This increase is correlated with a simultaneous decrease in phosphocreatine, whereas the energy charge of the muscles was essentially unaffected by the applied tetani. The time course of the rise in Fru(1,6)P2 was used to model changes in the free concentrations of high-affinity aldolase-binding inositol phosphates during the course of a tetanus. These calculations demonstrate that the free concentration of Ins(1,4,5)P3 and other aldolase-bound inositol phosphates can increase much faster and to a larger extent than the corresponding total concentrations as a result of their competitive displacement from aldolase-binding sites by the rapidly rising concentration of Fru(1,6)P2.
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PMID:Masses of inositol phosphates in resting and tetanically stimulated vertebrate skeletal muscles. 176 26

Skeletal muscle triads are possessing the whole set of enzymes of the phosphatidylinositol (PI)-linked signal generating pathway, PI-kinase, PI(4)P-kinase, and PI(4,5)P2-phospholipase C (PLC). The activities of these enzymes are comparable to those found in other cell types for which a functional role of the PI-pathway in intracellular signal transduction has been established. For skeletal muscle an unequivocal function and an initiating signal for Ins(1,4,5)P3-liberation is still unknown. However, the observed Ca-dependency of PLC activity suggests that here Ins(1,4,5)P3 production is a consequence rather than a cause of increasing cytosolic Ca2+. Recently, the glycolytic enzyme aldolase, whose activity can be modulated by inositol polyphosphates, has been localized in the triadic structure. The enzyme which has a high affinity to Ins(1,4)P2, Ins(1,4,5)P3 and Ins(1,3,4,5)P4, seems to be compartmentalized to the junctional foot structure from which it is released upon binding of these molecules. This phenomenon could reflect a capability for regulation of the glycolytic flux even for aldolase, especially if a non steady-state situation in the junctional gap is considered. Meanwhile we have accumulated evidence for the operation of a partial glycolytic sequence in the junctional region established by the enzymes aldolase, glyceraldehyde-3-P (GAP) dehydrogenase and phosphoglycerate kinase. This system is able to produce ATP upon oxidation of GAP and could be, because of the inositol polyphosphate-sensing abilities of aldolase, a target for the membrane associated PI-pathway. The ATP production is however transient which indicates the coupling to an ATP hydrolyzing reaction.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Relation of phosphatidylinositol metabolism to glycolytic pathway in skeletal muscle membranes. 228 42

The effects of inositol 1,4,5-trisphosphate (Ins(1,4,5)P3), which has been hypothesized to be a chemical transmitter in excitation-contraction coupling in skeletal muscle, on aldolase bound to isolated triad junctions were investigated. Fructose-1,6-bisphosphate aldolase was identified as the major specific binding protein for the Ins(1,4,5)P3 analogue glycolaldehyde (2)-1-phospho-D-myo-inositol 4,5-bisphosphate which can form covalent bonds with protein amino groups by reduction of the Schiff's base intermediate with [3H]NaCNBH3. This analogue, Ins(1,4,5) P3, and the inositol polyphosphates inositol 1,3,4,5-tetrakisphosphate and inositol 1,4-bisphosphate were nearly equipotent in selectively releasing membrane bound aldolase with a K0.5 of about 3 microM. The rank order of the K0.5 values was identical to the KI values for inhibition of aldolase. Aldolase was also released by its substrate fructose 1,6-bisphosphate and by 2,3-bisphosphoglycerate. Ins(1,4,5)P3-induced aldolase release did not disrupt the triad junction; glyceraldehyde-3-phosphate dehydrogenase, a known junctional constituent, was displaced only at much higher Ins(1,4,5)P3 concentrations. Ins(1,4,5)P3 was as effective as fructose 1,6-bisphosphate in releasing aldolase from myofibrils. A finite number of binding sites for aldolase exist on triads (Bmax = 43-47 pmol of tetrameric aldolase exist on triads (Bmax = 43-47 pmol of tetrameric aldolase/mg of triad protein, KD = 23 nM). The junctional foot protein was implicated as an aldolase binding site by affinity chromatography with the junctional foot protein immobilized on Sepharose 4B. The potential consequences of aldolase being bound in the gap between the terminal cisternae and the transverse tubule to inositol polyphosphate and glycolytic metabolism in that local region are discussed.
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PMID:Inositol polyphosphate-mediated repartitioning of aldolase in skeletal muscle triads and myofibrils. 278 11

A cytoskeletal fraction of porcine tracheal smooth muscle (PTSM) was found to contain > 90% of total cellular aldolase (fructose 1,6-bisphosphate aldolase, EC 4.1.2.13) activity. PTSM aldolase was purified by DEAE and inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) affinity chromatography and found to react with an antibody directed against human aldolase C, but not anti-aldolase A and B. The molecular mass of native aldolase was about 138 kDa (on Sephacryl S-300); SDS-denatured enzyme was 35 kDa (comigrated with rabbit skeletal muscle aldolase). Total cellular aldolase tetramer (aldolase4) content was 34.5 pmol/100 nmol lipid P(i). Ins(1,4,5)P3) binding activity coeluted with aldolase during Sephacryl 300, DEAE, and Ins(1,4,5)P3 affinity chromatography. Ins(1,4,5)P3 bound to purified aldolase (at 0 degree C) in a dose-dependent manner over the range [Ins(1,4,5)P3] 20 nM to 20 microM, with maximal binding of 1 mol of Ins(1,4,5)P3/mol aldolase4 and a Kd of 12-14 microM. Fru(1,6)P2 and Fru(2,6)P2 displaced bound Ins(1,4,5)P3) with a 50% inhibition at 30 and 170 microM, respectively. Ins(1,3,4)P3 (20 microM) and glyceraldehyde 3-phosphate (2 mM) were also potent inhibitors of Ins(1,4,5)P3 binding, but not inositol 4-phosphate or inositol 1,4-bisphosphate (20 microM each). Aldolase-bound Ins(1,4,5)P3 may play a role in phospholipase C-independent increases in free [Ins(1,4,5)P3].
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PMID:Inositol 1,4,5-trisphosphate binding to porcine tracheal smooth muscle aldolase. 765 22

We substituted neutral amino acids for some positively charged residues (R42, K107, K146, R148 and K229) that line the active site of aldolase A in an effort to determine binding sites for inositol 1, 4,5-trisphosphate. In addition, D33 (involved in carbon-carbon bond cleavage) was mutated. K229A and D33S aldolases showed almost no catalytic activity, but Ins(1,4,5)P(3) binding was similar to that determined with the use of wild-type aldolase A. R42A, K107A, K146R and R148A had markedly decreased affinities for Ins(1,4,5)P(3) binding, increased EC(50) values for Fru(1,6)P(2)-evoked release of bound Ins(1,4,5)P(3) and increased K(i) values for Ins(1,4, 5)P(3)-evoked inhibition of aldolase activity. K146Q (positive charge removal) had essentially no catalytic activity and could not bind Ins(1,4,5)P(3). Computer-simulated docking of Ins(1,4,5)P(3) in the aldolase A structure was consistent with electrostatic binding of Ins(1,4,5)P(3) to K107, K146, R148, R42, R303 and backbone nitrogens, as has been reported for Fru(1,6)P(2) binding. Results indicate that Ins(1,4,5)P(3) binding occurs at the active site and is not dependent on having a catalytically active enzyme; they also suggest that there is competition between Ins(1,4,5)P(3) and Fru(1, 6)P(2) for binding. Although Ins(1,4,5)P(3) binding to aldolase involved electrostatic interactions, the aldolase A Ins(1,4, 5)P(3)-binding domain did not show other similarities to pleckstrin homology domains or phosphotyrosine-binding domains known to bind Ins(1,4,5)P(3) in other proteins.
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PMID:Aldolase A Ins(1,4,5)P3-binding domains as determined by site-directed mutagenesis. 1041 47