Purification and properties of the first-identified, archaeal, ATP-dependent 6-phosphofructokinase, an extremely thermophilic non-allosteric enzyme, from the hyperthermophile Desulfurococcus amylolyticus.
The ATP-dependent 6-phosphofructokinase (ATP-PFK) of the hyperthermophilic archaeon Desulfurococcus amylolyticus was purified 1,500-fold to homogeneity. The enzyme had an apparent molecular mass of 140 kDa and was composed of a single type of subunit of 33 kDa suggesting a homotetrameric (alpha4) structure. The N-terminal amino acid sequence did not show significant similarity to ATP-PFKs isolated from eubacteria and eukarya. Kinetic constants of the enzyme were determined for both reaction directions at pH 6 and at 85 degrees C. Rate dependence on all substrates followed Michaelis-Menten kinetics. The apparent K(m)s for ATP and fructose 6-phosphate (forward reaction) were 0.28 and 1.17 mM, respectively; the apparent V(max) was about 41 U/mg. ATP could not be replaced by pyrophosphate (PPi) or ADP as phosphoryl donor, thus defining the enzyme as an ATP-dependent PFK. In addition to ATP (100%), the enzyme accepted GTP (97%), ITP (130%), UTP (84%), CTP (55%) and, less effectively, acetyl phosphate (13%) as phosphoryl donors. Enzyme activity was not allosterically regulated by classical effectors of ATP-PFKs such as ADP, AMP, and phosphoenolpyruvate or citrate. The enzyme also catalysed in vitro the reverse reaction with an apparent K(m) for fructose-1,6-bisphosphate and ADP of 16.7 and 0.5 mM, respectively, and an apparent V(max) of about 4.5 U/mg. Divalent cations were required for maximal activity; Mg2+, which was most effective, could be replaced partially by Ni2+, Mn2+ or Co2+. The enzyme had a temperature optimum of 90 degrees C and showed a significant thermostability up to 100 degrees C, which is in accordance with its physiological function under hyperthermophilic conditions. This is the first description of an ATP-dependent PFK from the domain of archaea, characterized as an extremely thermophilic, non-allosteric enzyme.
Hansen
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Institut für Allgemeine Mikrobiologie, Christian-Albrechts-Universität Kiel, Germany.
Schönheit
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D000255:Adenosine Triphosphate / Q000378:metabolism*; D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D019620:Desulfurococcaceae / Q000201:enzymology*; D005947:Glucose / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010732:Phosphofructokinase-1 / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism*; D013379:Substrate Specificity; D013696:Temperature
D000255:Adenosine Triphosphate; D010732:Phosphofructokinase-1; D005947:Glucose