ATPγS tetralithium salt

Adenosine 5'-O-(3-thio)triphosphate (ATPgammaS) is a substrate for the nucleotide hydrolysis and RNA unwinding activities of eukaryotic translation initiation factor eIF4A.[Pubmed:13130132]

RNA. 2003 Oct;9(10):1180-7.

Whereas ATPgammaS is often considered a nonhydrolyzable substrate for ATPases, we present evidence that ATPgammaS is a good substrate for the RNA-stimulated nucleotide hydrolysis and RNA unwinding activities of eIF4A. In the presence of saturating single-stranded poly(U) RNA, eIF4A hydrolyzes ATPgammaS.Mg and ATP.Mg with similar steady-state parameters (KM(NTP.Mg) = 66 and 58 microM and kcat = 1.0 and 0.97 min(-1), respectively). ATPgammaS.Mg also supports catalysis of RNA unwinding within 10-fold of the rate supported by ATP.Mg. The identical steady-state rate parameters, in comparison with the expected difference in the intrinsic rate of hydrolysis for ATP and ATPgammaS, suggest a nonchemical rate-limiting step for nucleotide hydrolysis. These results raise caution concerning the assumption that ATPgammaS is a nonhydrolyzable ATP analog and underscore the utility of thio-substituted NTPs as mechanistic probes.

Pharmacological characterization of heterologously expressed ATP-gated cation channels (P2x purinoceptors).[Pubmed:7544432]

Mol Pharmacol. 1995 Aug;48(2):178-83.

cDNAs encoding P2x purinoceptors from human bladder smooth muscle and from rat PC-12 cells were expressed in oocytes and human embryonic kidney 293 cells. Agonist potencies of 2-methylthio-ATP = 2-chloro-ATP = ATP > = 2'- and 3'-O-(4-benzoylbenzoyl)-ATP > or = adenosine-5'-O-(3-thio)-triphosphate > or = P1,P5-di(adenosine-5') pentaphosphate >> ADP prevailed for both P2x purinoceptors. There were two main differences in agonist sensitivity between the two receptors. First, ATP was 10 times more potent at the receptor from bladder (EC50, 0.8 microM) than at the receptor from PC-12 cells (EC50, 8.2 microM). Second, alpha,beta-methylene-ATP and L- and D-beta,gamma-methylene-ATP were agonists in cells expressing the bladder smooth muscle receptor (EC50, 1-3 microM) but were ineffective in cells expressing the PC-12 receptor. The P2 purinoceptor antagonists suramin, pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid, and pyridoxal-5-phosphate acted similarly at both receptor forms, producing noncompetitive inhibition, with IC50 values of 1-5 microM for suramin and pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid and 10-20 microM for pyridoxal-5-phosphate. 4,4'-Diisothiocyanatostilbene-2,2'-disulfonic acid distinguished receptor subtypes, producing potent inhibition of the bladder smooth muscle P2x-mediated response, with an IC50 value of 3 microM; it inhibited the PC-12 form by < 40% at 100 or 300 microM. This study thus defines the pharmacological properties of homo-oligomeric forms of these two types of cloned P2x receptor channels.