Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have shown previously that radiolabelled phosphatidylcholine (PC) in liposomes or natural surfactant is removed from the alveolar space and metabolically recycled in a process that is stimulated by cyclic AMP (cAMP). In this study, we evaluated the effect of a transition-state phospholipid analogue (MJ33; 1-hexadecyl-3-trifluoroethylglycero-sn-2-phosphomethanol) that competitively inhibited acidic phospholipase A2 (PLA2) activity (pH 4.0) of lung homogenate by more than 97%, but had no effect on PLA2 activity at pH 8.5. MJ33 incorporated into unilamellar liposomes (dipalmitoyl PC/egg PC/cholesterol/phosphatidylglycerol, molar proportions 10:5:3:2) or co-sonicated with biosynthesized natural surfactant was instilled into the trachea of the anaesthetized rat; lungs were then removed for 2 h perfusion in the absence or presence of 0.1 mM-8-bromo cAMP. Total uptake for phospholipid was unchanged in the presence of the inhibitor MJ33. Degradation of labelled PC during 2 h perfusion in the absence of MJ33 was approx. 26% of that instilled for choline-labelled liposomal PC, 16% for liposomal PC labelled in the second fatty-acyl position, and 33% for choline-labelled natural surfactant. Degradation of PC was decreased by approx. 25-40% for each substrate in the presence of MJ33. Inhibition of lipid degradation depended on the mole fraction of MJ33 in the liposomes and was maximal at 1 mol%. These studies demonstrate a significant role for acidic Ca(2+)-independent PLA2 in the degradation of internalized alveolar PC, but further indicate that this enzyme accounts for a minor fraction of total lung PC metabolism.
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PMID:A competitive inhibitor of phospholipase A2 decreases surfactant phosphatidylcholine degradation by the rat lung. 146 44

The relationship between derivatization of reactive cysteine residues with N-ethylmaleimide and a partial desensitization of fructose 1,6-bisphosphatase to AMP inhibition was studied. AMP desensitization of the enzyme was found to be dependent on the activity assay conditions used. When the assay was performed in the presence of high levels of monovalent cations (150 mM), the AMP affinity of the enzyme decreased with the chemical modification. The apparent loss of sensitivity toward AMP was accompanied by an uptake of 1 mole of N-ethylmaleimide/mole of enzyme subunit. However, the modified enzyme did not show alteration in AMP inhibition in the absence of K+. Evidence was obtained that K+ induces a conformational change on the enzyme derivative, which hinders AMP interaction with the protein. The results point to the importance of selecting suitable conditions for the study of the regulatory properties in allosteric enzymes.
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PMID:The interaction of monovalent cations with fructose 1,6-bisphosphatase modified by N-ethylmaleimide and its relation with AMP inhibition. 155 47

Atrial natriuretic factor (ANF) stimulates accumulation of cyclic GMP in a photosensitive organ, as evidenced for the first time in cultured trout pineals. Stimulation was rapid (within a few min), dose-dependent, and stronger in organs cultured in darkness than in those cultured under light. After 30 min in the dark, (i) cyclic AMP levels were slightly increased at 10(-7) mole/l of ANF, (ii) cyclic GMP and cyclic AMP increased dramatically after inhibition of the phosphodiesterases by isobutylmethylxanthine (IBMX), (iii) ANF and IBMX effects were more than additive on cyclic GMP, (iv) pertussis toxin decreased the cyclic GMP response to ANF. These responses were affected by light. The possibility that cyclic GMP might be a second messenger of both light and chemical (ANF) inputs, in pineal photoreceptor cells, is hypothetized.
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PMID:Atrial natriuretic factor increases cyclic GMP and cyclic AMP levels in a directly photosensitive pineal organ. 170 18

The ocular penetration of 14C-forskolin in suspension was studied using albino rabbits. The effects of topical forskolin suspension on cyclic AMP (cAMP) synthesis, aqueous flow and intraocular pressure (IOP) were also studied. It was shown that only 0.03% of the instilled forskolin penetrated the ocular tissue. The calculated kep value for forskolin was 0.2 X 10(-4) cm/hr. The peak concentrations were calculated to be 4 X 10(-7) mole/liter, 4.6 X 10(-7) and 2.7 X 10(-7) mole/1,000 g tissue in aqueous, iris and ciliary body, respectively, after instillation of 1% forskolin suspension. Topical 1% forskolin suspension caused cAMP increase in the aqueous humor 30 minutes after instillation, but cAMP returned to baseline level 60 minutes after instillation. The cAMP level in the ciliary body was not increased by forskolin. Aqueous flow did not change, and the IOP was slightly decreased 45 and 60 minutes after instillation of forskolin suspension. The in vivo least-effective concentration of forskolin in the ciliary epithelium was considered to be about 2.7 X 10(-7) mole/1,000 g tissue. The weak IOP lowering effect of topical forskolin suspension was considered to be due to its poor ocular penetration. However, slight modification of molecular structure might increase ocular penetration. Present results suggest only a slight increase in penetrative potential would be needed to make forskolin effective in antiglaucoma therapy.
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PMID:The ocular penetration of topical forskolin and its effects on intraocular pressure, aqueous flow rate and cyclic AMP level in the rabbit eye. 196 83

ATP-binding sites in the unphosphorylated Ca2(+)-ATPase of sarcoplasmic reticulum vesicles were titrated with 2',3'-O-(2,4,6-trinitrocyclohexadienylidene)-[3H]AMP (TNP-AMP) or -[3H]ATP (TNP-ATP) in the absence of Ca2+ at pH 7.0 and 0 degrees C by using a centrifugation procedure. In some measurements, the bound TNP-nucleotides were chased with ATP. The data were analyzed by best-fit computer programs as well as by Scatchard plots. The results showed the existence of 1 mol of TNP-AMP binding sites with high affinity (Kd = 7.62 nM) per mole of phosphorylatable sites. The affinity of these sites for ATP (Kd = 10.1 microM) agreed with that of catalytic sites for ATP in the absence of Ca2+. The results further showed the existence of 2 mol of TNP-ATP binding sites with uniform affinity (Kd = 156 nM) per mole of phosphorylatable sites. Half of the bound TNP-ATP was fully chased by low concentrations of ATP. The affinity of this class of the sites for ATP (Kd = 8.9 microM) again agreed with that of catalytic sites for ATP. The other half of the bound TNP-ATP was fully chased only by much higher concentrations of ATP. Thus, the affinity of this class of the sites for ATP (Kd = 791 microM) was much lower than that of catalytic sites for ATP. Similar measurements were performed with sarcoplasmic reticulum vesicles pretreated by N-(iodoacetyl)-N'-(5-sulfo-1-naphthyl)ethylenediamine. Although the affinities for TNP-ATP and for ATP were appreciably altered by this pretreatment, the results were essentially the same as those obtained with native vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Existence of a low-affinity ATP-binding site in the unphosphorylated Ca2(+)-ATPase of sarcoplasmic reticulum vesicles: evidence from binding of 2',3'-O-(2,4,6-trinitrocyclohexadienylidene)-[3H]AMP and -[3H]ATP. 214 72

Cyclic AMP-dependent phosphorylation of the rat brain sodium channel was reported to be restricted to five sites within an approximately 210 amino acid region of the primary sequence that is deleted in the homologous sodium channel from rat skeletal muscle. We find that, in spite of this deletion, the rat muscle sodium channel alpha-subunit is also an excellent substrate for phosphorylation by this kinase both in primary muscle cells in tissue culture and in vitro after isolation from adult muscle. Sodium channel protein purified from adult rat skeletal muscle was readily phosphorylated in vitro by the catalytic subunit of the bovine cyclic AMP-dependent protein kinase (PKa). Only the 260,000 MW alpha-subunit was labeled, with a maximum level of incorporation in vitro of approximately 0.5 mol [32P]phosphate per mole of channel protein. The beta-subunit of the channel is not phosphorylated under these conditions. In primary rat skeletal muscle cells in culture, incorporation of phosphate into the channel alpha-subunit is stimulated 1.3- to 1.5-fold by treatment of the cells with forskolin. Phosphorylation of the sodium channel isolated from these cells could also be demonstrated in vitro using PKa. This in vitro phosphorylation could be inhibited 80-90% by pretreatment of the cells in culture with forskolin, suggesting that the sites labeled in vitro by PKa were the same as those phosphorylated in the intact cells by the endogenous cyclic AMP-dependent kinase. In both the adult muscle channel and the channel from muscle cells in culture, phosphorylation by PKa was limited to serine residues.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Phosphorylation of the rat skeletal muscle sodium channel by cyclic AMP-dependent protein kinase. 215 54

Human term placenta contains an ATP diphosphohydrolase activity which hydrolyses ATP to ADP and inorganic phosphate and ADP to AMP and a second mole of inorganic phosphate. The activity has a pH optimum between 8.0 and 8.5. Magnesium or calcium ions are required for maximum activity. Other nucleoside phosphates, p-nitrophenyl phosphate or sodium pyrophosphate, are not hydrolysed. The activity is not due to ATPases, or to myokinase, as determined by the use of inhibitors. NaF and NaN3 were found to inhibit strongly the activity thus identifying it as an ATP diphosphohydrolase. A sensitive enzymatic assay for measurement of AMP, one of the products of the reaction, was established, based on the strong inhibition of muscle fructose 1,6-biphosphatase by AMP. The range of the assay was 0.05-0.8 microM AMP. ATP diphosphohydrolase was found to have a rate of AMP production from ADP twice the rate from ATP. Under the same conditions, the assay for Pi release, on the other hand, gave velocities similar to each other for the two substrates. The activity appears to be identical to the ADP-hydrolysing activity in placenta reported by others.
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PMID:Identification of ATP diphosphohydrolase activity in human term placenta using a novel assay for AMP. 217 97

Ribonuclease (RNase) T2 from Aspergillus oryzae was modified by diethyl pyrocarbonate and iodoacetic acid. RNase T2 was rapidly inactivated by diethyl pyrocarbonate above pH 6.0 and by incorporation of a carboxymethyl group. No inactivation occurred in the presence of 3'AMP. 1H-NMR titration and photo-chemically induced dynamic nuclear polarization experiments demonstrated that two histidine residues were involved in the active site of RNase T2. Furthermore, analysis of inactive carboxymethylated RNase T2 showed that both His53 and His115 were partially modified to yield a total of one mole of N tau-carboxymethylhistidine/mole enzyme. The results indicate that the two histidine residues in the active site of RNase T2 are essential for catalysis and that modification of either His53 or His115 inactivates the enzyme.
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PMID:Identification of two essential histidine residues of ribonuclease T2 from Aspergillus oryzae. 229 7

The effect of phosphorylation by cyclic AMP dependent protein kinase on the assembly of the core-forming 68 KDa neurofilament subunit protein (NF-L) was studied in vitro by fluorescence energy transfer and electron microscopy. Phosphorylation of unassembled NF-L in a low ionic strength buffer by cyclic AMP dependent protein kinase led to the incorporation of 1-2 phosphate groups/mole protein. Assembly of this phosphorylated NF-L was inhibited significantly; compared to non-phosphorylated NF-L, the critical concentration of phosphorylated NF-L was raised by greater than 30-fold. Assembled NF-L filaments could also be phosphorylated by cyclic AMP dependent protein kinase indicating that the sites were accessible. Phosphorylation of NF-L in the filamentous state induced their disassembly. The results suggest that phosphorylation by cyclic AMP dependent protein kinase is a possible means to modulate the assembly state of NF-L.
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PMID:Effect of phosphorylation on 68 KDa neurofilament subunit protein assembly by the cyclic AMP dependent protein kinase in vitro. 235 30

1. Multiple conductance level ion channels were recorded in excised and cell-attached patches from cells of a mouse B lymphocyte hybridoma line. The reversal potential for the single-channel current was unaffected by the species of cation on the cytoplasmic face of the patch, but changed as the Cl- concentration was altered, indicating that the channel is anion selective. 2. The permeability sequence determined from reversal potentials was F- greater than I- greater than SCN- greater than Br- greater than Cl- greater than glucuronate greater than NO3- greater than aspartate. This was different from the conductance sequence (Cl- greater than SCN- = F- greater than Br- greater than NO3- greater than I- greater than glucuronate greater than aspartate), indicating interaction of ions within the pore of the channel. Consistent with this was the observation of anomalous mole fraction dependence with a mixed solution of thiocyanate and chloride. 3. In addition to the main open level (about 400 pS; excised patch, symmetrical 165 mM-Cl-), three subconductance levels and one supraconductance level were observed. These were concluded to be integral components of the same channel based on coincidence of appearance and identical permeabilities. 4. The channel is voltage dependent, with open probability in excised patches increasing with more positive potentials. The channel was reversibly blocked in a voltage-dependent manner by SITS (4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid), a stilbene derivative, on the cytoplasmic face. 5. Several differences were noted between cell-attached and excised-patch recordings. The multiple conductance level channel was less frequently seen in cell-attached patches but could often be induced to appear by prolonged application of positive voltages. This induced channel in attached patches showed an altered voltage dependence which could be partially mimicked in excised patches by including cyclic AMP and ATP in the solution on the cytoplasmic side of the membrane.
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PMID:Anion channels with multiple conductance levels in a mouse B lymphocyte cell line. 247 28


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