Sarcoplasmic Reticulum

Pucell, Anthony G.; Martonosi, Anthony

doi:10.1016/s0021-9258(18)62236-7

Cited by 90 publications

(10 citation statements)

References 25 publications

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“…Therefore, the phosphorylation reaction and the subsequent calcium translocation must be completed within a time shorter than that required for Ca2+ dissociation from the high-affinity solvent-accessible sites. This rate limit (17 s-1) has been observed by Sumida et al (1978) and by Rauch et al (1978).…”

Section: Discussionsupporting

confidence: 65%

“…Steady-State Kinetics. SR vesicles utilize a variety of high-energy phosphate ester substrates for coupling the phosphorolytic reaction to active Ca2+ transport (Makinose & The, 1965;de Meis, 1969;Friedman & Makinose, 1970;Pucell & Martonosi, 1971;Rossi et al, 1979;Kurzmack et al, 1979). Comparative measurements of Ca2+ uptake by SR vesicles following addition of ATP, ITP, FAP, AcP, and PNPP at nearly saturating concentrations are shown in Figure 1.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Transient-state kinetic studies on the mechanism of furylacryloylphosphatase-coupled calcium ion transport with sarcoplasmic reticulum adenosine triphosphatase

Kurzmack¹,

Inesi²,

Tal³

et al. 1981

Biochemistry

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Section: Discussionsupporting

confidence: 65%

Section: Resultsmentioning

confidence: 99%

Transient-state kinetic studies on the mechanism of furylacryloylphosphatase-coupled calcium ion transport with sarcoplasmic reticulum adenosine triphosphatase

Kurzmack¹,

Inesi²,

Tal³

et al. 1981

Biochemistry

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“…Competition between P¡ and nucleoside phosphates for the same site, or possibly for two sites of different affinities, has been suggested by Pucell & Martonosi (1971) and by Hasselbach & Mígala (1977). Our data on the stabilization of Mg3E, by P¡ are not sufficient to distinguish whether one or two sites are involved.2…”

Section: Discussionmentioning

confidence: 53%

“…There are previous indications of association between P¡ and E, from the work of Pucell &Martonosi (1971) andMígala (1977),…”

mentioning

confidence: 94%

Phosphorylation of calcium ATPase by inorganic phosphate: reversible inhibition at high magnesium ion concentrations

Loomis¹,

Martin²,

McCaslin³

et al. 1982

Biochemistry

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Magnesium stimulates phosphorylation of the calcium pump protein of the sarcoplasmic reticulum by inorganic phosphate, but the effect is reversed by high [Mg2+]. This reversal is readily explained in terms of the generally accepted existence of two conformational states of the enzyme, E1 and E2. E2 is the form of the enzyme that can be phosphorylated by Pi, and it has one binding site for Mg2+. E1 is the form of the enzyme that has two high-affinity Ca2+ binding sites, and it is phosphorylated by ATP when Ca2+ is bound. Mg2+ can bind weakly to the two Ca2+ sites and to a third site known to be present on E1; this stabilizes E1 at the expense of E2 when [Mg2+] is large. Stabilization of E1 at pH 6.2 and 25 degrees C was found to be a highly cooperative function of [Mg2+] and was not prevented by increasing [Pi]. The latter result requires the existence of a binding site for Pi on E1, with an affinity for Pi comparable to that of E2. Cooperativity with respect to [Mg2+] requires that E2 is the stable state of the enzyme in the absence of ligands, with an equilibrium constant [E2]/[E1] on the order of 10(3) or higher at pH 6.2 and 25 degrees C.

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“…Synthesis of the acyl phosphate requires removal of a hydroxyl group from inorganic phosphate, a difficult reaction, and is accelerated at the active site by a factor of 1015 compared with the nonenzymic reaction (Pickart & Jencks, 1984). The enzyme also reacts in the absence of calcium with strongly activated chemical phosphorylating agents, such as acyl phosphates and phosphate esters with acidic leaving groups, but these reactions are far slower than the reaction with inorganic phosphate (Pucell & Martonosi, 1971; Rossi et al, 1979; Inesi et al, 1980;Liguri et al, 1980;Kurzmack et al, 1981;Bodley & Jencks, 1987).…”

mentioning

confidence: 99%

Specificity of the sarcoplasmic reticulum calcium ATPase at the hydrolysis step

Chipman¹,

Jencks²

1988

Biochemistry

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The coupling of Ca2+ transport to ATP hydrolysis by the SR ATPase requires that the enzyme operate with considerable specificity, which is different at different steps. The limits of specificity of the calcium-free phosphorylated enzyme for transfer of its phosphoryl group to water have been examined. The rate of transfer of the phosphoryl group to the simple nucleophile methanol was compared to its transfer to water by following the formation of methyl phosphate from inorganic phosphate. The reverse reaction, hydrolysis of methyl phosphate, was compared to phosphate-water oxygen exchange. The reactions involving methanol as nucleophile or leaving group are at least 2-3 orders of magnitude slower than those involving water. This result indicates that the transition state for this reaction involves strong and specific interactions of the H2O molecule with the enzyme. These interactions may also involve the bound Mg2+ ion. The results also suggest that the difference in specificity between Ca2+ free and Ca2+ bound states of the enzyme involves significant differences in the structure of the catalytic site.

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Sarcoplasmic Reticulum

Cited by 90 publications

References 25 publications

Transient-state kinetic studies on the mechanism of furylacryloylphosphatase-coupled calcium ion transport with sarcoplasmic reticulum adenosine triphosphatase

Transient-state kinetic studies on the mechanism of furylacryloylphosphatase-coupled calcium ion transport with sarcoplasmic reticulum adenosine triphosphatase

Phosphorylation of calcium ATPase by inorganic phosphate: reversible inhibition at high magnesium ion concentrations

Specificity of the sarcoplasmic reticulum calcium ATPase at the hydrolysis step

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