title: ATPase activity of biotin carboxylase provides evidence for initial activation of HCO3- by ATP in the carboxylation of biotin.
abstract: When we incubated biotin carboxylase from Escherichia coli with ATP in absence of biotin we observed HCO3- -dependent ATP hydrolysis, which was activated by 10% ethanol in the same proportion as the activity of D-biotin carboxylation assayed in the presence of biotin. The two activities exhibited identical heat stability and were protected equally by glycerol; both required Mg2+ and K+ and showed similar dependency on the concentration of ATP. Biotin assay excluded potential contamination by traces of biotin as a cause of the observed ATP hydrolysis, and this was confirmed by the findings that carboxybiotin did not accumulate and that avidin was uninhibitory. Therefore we concluded that this HCO3- -dependent ATPase was genuinely a partial activity of biotin carboxylase. This partial activity supports a sequential mechanism for enzymatic carboxylation of biotin in which HCO3- is activated by ATP in a first step. It is consistent with the initial formation of the carbonic-phosphoric anhydride (HOCO2PO3(2-)), and it does not agree with models where biotin is phosphorylated by ATP prior to reaction with HCO3-. It appears that enzymes that use HCO3- for carboxylation, including biotin-dependent carboxylases, phosphoenolpyruvate carboxylase, and carbamoyl phosphate synthetase, activate HCO3- by a common mechanism involving the initial formation of the carbonic-phosphoric anhydride.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D001639:Bicarbonates / Q000378:metabolism*; D001711:Biotransformation; D019731:Carbon-Nitrogen Ligases; D007700:Kinetics; D008025:Ligases / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D013696:Temperature
chemical_list: D001639:Bicarbonates; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D008025:Ligases; D019731:Carbon-Nitrogen Ligases; C019791:biotin carboxylase; D008274:Magnesium; D011188:Potassium