Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.16.2 (PCP)
 3,761 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

3H-labeled 9-methyl-7-bromoeudistomin D ([3H]MBED), a powerful caffeine-like Ca2+ releaser, binds to the caffeine binding site of terminal cisternae (TC) of skeletal muscle sarcoplasmic reticulum (SR) (Fang, Y-I., Adachi, M., Kobayashi, J., and Ohizumi, Y. (1993). J. Biol. Chem. 268, 18622-18625.) and activates Ca(2+)-induced Ca2+ release (CICR). [3H]MBED, however, bound to rabbit hepatic microsomes with a comparable affinity (Kd = 50 nM) and with a more than 30-fold greater receptor density (Bmax = 350 pmol/mg of protein), compared with those in SR. Caffeine (0.1-10 mM) caused a concentration dependent inhibition of [3H]MBED binding to hepatic microsomes with the IC50 value of 0.3 mM. The mode of inhibition by caffeine was allosteric, indicating that the binding site of the ligand is distinct from but related to that of caffeine. Procaine (1-10 mM), a representative inhibitor of CICR, which suppresses [3H]MBED binding to TC-SR, inhibited ligand binding to hepatic microsomes only slightly. Moreover, ligand binding to the hepatic binding site was not affected by adenosine 5'-(beta, gamma-methylene) triphosphate (AMP-PCP) (10-100 microM), which is an activator of CICR and potentiates [3H]MBED binding to TC-SR. Inhibitors of [3H]MBED binding to liver microsomes other than caffeine were nucleotides such as ADP, ATP, GTP, UTP (1 mM), while CTP, cAMP, AMP, adenosine (1 mM), ryanodine (0.1-100 mM) and inositol 1,4,5-trisphosphate (1 microM) were not effective. These features of the hepatic microsomal [3H]MBED binding site distinguish it from that of skeletal muscle SR. [3H]MBED, which binds to the different sites which are both sensitive to caffeine, is useful as a probe to investigate the actions of caffeine at the molecular level.
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PMID:The specific binding site of 9-[3H]methyl-7-bromoeudistomin D, a caffeine-like Ca2+ releaser, in liver microsomes in distinct from that in skeletal sarcoplasmic reticulum. 801 Nov 74

The hepatocyte has an organic anion transport system that recognizes compounds such as bilirubin and sulfobromophthalein. These anions circulate bound tightly to albumin from which they are extracted rapidly by hepatocytes by an electroneutral process that requires extracellular inorganic anions such as Cl- for activity. Transport activity is reduced by depletion of intracellular ATP, but whether ATP interacts directly with this transporter is not known. In this study, the influence of extracellular ATP on the hepatocyte organic anion transport mechanism has been characterized. In the presence of 2.5 mM Ca2+ and 2 mM Mg2+, initial uptake of [35S]sulfobromophthalein was reduced by 50% at 1 mM ATP. In the absence of divalent cations sensitivity to ATP was 10-fold greater. Other nucleotides including UTP, CTP, GTP, ADP, AMP, and AMP-PCP (adenosine 5'-(beta,gamma-methylene)triphosphate) were inactive. Decreased transport activity was rapidly reversible, was non-competitive with respect to ATP, did not require ATP hydrolysis, and did not correlate with P2y purinergic receptor activity. Differential activity of ATP on sulfobromophthalein transport in the presence and absence of divalent cations was not due to ecto-ATPase activity but rather to alteration in [ATP4-]. Although an ATP4- receptor in macrophages mediates increased cellular permeability, reduced organic anion permeability is seen in hepatocytes. This effect is not seen in the hepatoma cell line HepG2. Modulation of activity of the organic anion transporter by extracellular ATP may have important pathophysiological consequences in conditions resulting in liver cell injury.
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PMID:Extracellular ATP4- modulates organic anion transport by rat hepatocytes. 834 Mar 70

Reticulomyxa transports particulates, like bacterial and algal prey items, bidirectionally along the outside of its pseudopodia. This cell surface transport and intracellular organelle transport can be reactivated in detergent permeabilized cell models [Orokos et al., 1997: Cell Motil. Cytoskeleton]. We have used this unique system to compare cell surface and organelle mechanochemistry in situ in the same reactivated pseudopodia. The ATPase activities of both types of transport were indistinguishable; each displayed identical nucleoside triphosphate specificity, transport ATPase kinetics, and inhibitor sensitivity. Organelle and cell surface transport reactivation required "hydrolyzable" adenosine nucleoside triphosphates; neither reactivated with GTP, CTP, UTP, ITP, AMP-PNP, AMP-PCP, or ATP-gamma-S. However, other ATP analogues, such as 2'-deoxy-ATP and 3'-deoxy-ATP and 2',3'-dideoxy-ATP, supported the reactivation of organelle and cell surface transport at similar, but markedly reduced, velocities. Both transport processes were inhibited similarly by known inhibitors of dynein ATPases such as erythro-9-(3-[2-hydroxynonyl]) adenine (EHNA) or sodium (Na)-orthovanadate. N-ethylmaleimide (NEM) and ultraviolet (UV) irradiation in the presence of Na-orthovanadate and ATP permanently disabled both transport processes. Organelle and surface transport followed identical Michaelis-Menten kinetics with a calculated Km of 118 microM ATP and a maximum translocation velocity (Vmax) of 8.33 microm/sec. These findings strongly suggest that cell surface transport shares the same cytoplasmic dynein motor [Schliwa et al., 1991: J. Cell Biol. 112:1199-1203] that drives organelle transport.
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PMID:Cell surface and organelle transport share the same enzymatic properties in Reticulomyxa. 938 17

We determined the effect of nucleotides and protein kinase A (PKA) on the Ca(2+)-dependent gating of the cloned intermediate conductance, Ca(2+)-dependent K(+) channel, hIK1. In Xenopus oocytes, during two-electrode voltage-clamp, forskolin plus isobutylmethylxanthine induced a Ca(2+)-dependent increase in hIK1 activity. In excised inside-out patches, addition of ATP induced a Ca(2+)-dependent increase in hIK1 activity (NP(o)). In contrast, neither nonhydrolyzable (AMP-PNP, AMP-PCP) nor hydrolyzable ATP analogs (GTP, CTP, UTP, and ITP) activated hIK1. The ATP-dependent activation of hIK1 required Mg(2+) and was reversed by either exogenous alkaline phosphatase or the PKA inhibitor PKI(5-24). The Ca(2+) dependence of hIK1 activation was best fit with a stimulatory constant (K(s)) of 350 nM and a Hill coefficient (n) of 2.3. ATP increased NP(o) at [Ca(2+)] >100 nM while having no effect on K(s) or n. Mutation of the single PKA consensus phosphorylation site at serine 334 to alanine (S334A) had no effect on the PKA-dependent activation during either two-electrode voltage-clamp or in excised inside-out patches. When expressed in HEK293 cells, ATP activated hIK1 in a Mg(2+)-dependent fashion, being reversed by alkaline phosphatase. Neither PKI(5-24) nor CaMKII(281-309) or PKC(19-31) affected the ATP-dependent activation. Northern blot analysis revealed hIK1 expression in the T84 colonic cell line. Endogenous hIK1 was activated by ATP in a Mg(2+)- and PKI(5-24)-dependent fashion and was reversed by alkaline phosphatase, whereas CaMKII(281-309) and PKC(19-31) had no effect on the ATP-dependent activation. The Ca(2+)-dependent activation (K(s) and n) was unaffected by ATP. In conclusion, hIK1 is activated by a membrane delimited PKA when endogenously expressed. Although the oocyte expression system recapitulates this regulation, expression in HEK293 cells does not. The effect of PKA on hIK1 gating is Ca(2+)-dependent and occurs via an increase in NP(o) without an effect on either Ca(2+) affinity or apparent cooperativity.
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PMID:Kinase-dependent regulation of the intermediate conductance, calcium-dependent potassium channel, hIK1. 1061 55


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