TABLE 3

Archaeal inorganic pyrophosphatases (E.C. 3.6.1.1) of the class A type (IPR008162 family)

CharacteristicPPA from:
Thermoplasma acidophilum (4, 35, 36)Pyrococcus horikoshii (5, 3739)Sulfolobus (4044)Methanothermobacter thermautotrophicus (45)Thermococcus thioreducens (46; unpublished data)Haloferax volcanii (this study)
Gene locus tagaTa0399PH1907STK_05240 Saci_0955MTH_263 (presumed)H0USY5_9EURYHVO_0729
No. of amino acids179178172–173176178177
pI (theoretical)5.334.974.83–4.92 (observed, 4.8)4.694.763.98
Molecular mass, kDa
    Theoretical20.520.819.420.120.920.4
    Observed6 × 226 × 24.5(4–6) × (17–21)(2–4) × 25b(3–6) × 27
Cation dependenceMg2+Mg2+; Co2+, Zn2+, Mn2+ (partial)Mg2+; Co2+, Zn2+, Mn2+ (partial)Mg2+; Co2+ (partial)Mg2+, Mn2+
Inhibitor(s)Ca2+, phenylgloyxalNaFNaF, Ca2+, phenylgloyxalNaFNaF
Substrate(s) hydrolyzedPPiPPi (P3, 2.7%; ATP, 5.9%; ADP, 2.9%)PPi (pNP, PEP, 1–2%; ATP, P3, ADP, 3–6%; TTP, ITP, 10%)PPiPPi
Km7 μM PPi, 1.7 mM Mg2+14–11 μM PPi, 0.3 mM Mg2+5 μM PPi, 0.9 mM Mg2+0.16 mM PPi, 4.9 mM Mg2+0.55 mM PPi (42°C), 0.26 mM PPi (25°C), 13.4 mM Mg2+(25°C)
Vmax, U · g−1c1,100 (56°C)930 (60°C)860 (75°C)570465 (42°C), 53 (25°C)
kcat, s−12,200744–3,4361,7001,050
Hill coefficient(s)1.8 (Mg2+)Cooperative binding1.9 (Mg2+)3.3 (PPi), 2.0 (Mg2+)2.1 (PPi, 42°C), 1.4 (PPi, 25°C), 2.6 (Mg2+, 25°C)
Temp, optimum, °C8570–88757042
pH, optimum7.5–106.5–7.07.7 (60°C)8.5 (25°C)
Thermal inactivation (half-life)50 min (105°C)2.5 h (95°C), >24 h (75°C)2 h (65°C)
Soluble, cytoplasmicYesYesYesYesYes
Heterologous systemE. coliE. coliE. coliE. coli
Crystal structure, PDB no.1UDE1QEZ3Q4W, 3I98, 3R5U, 3R5V, 3R6E, 3Q9 M
Coupled assayDNA polymerase (PCR, sequencing)DNA polymerase (PCR)Ub/Ubl adenylation
  • a Accession numbers: HVO_0729, D4GT97; PH1907, O59570; Ta0399, P37981; MTH_263, O26363; STK_05240, Q974Y8; Saci_0955, P50308; H0USY5_9EURY, H0USY5. Sulfolobus species included S. acidocaldarius ATCC 33909 and S. tokodaii strain 7.

  • b —, not reported.

  • c U · mg−1 is μmol PPi hydrolyzed min−1 (mg protein)−1. Vmax is the highest reported.