Unusual pKa of the carboxylate at the putative catalytic position of the thermophilic F1-ATPase β subunit determined by 13C-NMR

Abstract Glutamic acid-190 in the β subunit of F 1 -ATPase from thermophilic Bacillus PS-3 (TF 1 ) was reporte to be essential for the ATPase activity. The mutant TF 1 β subunit in which Glu-190 had been substituted by cysteine was carboxymethylated with 13 C-labeled monoiodoacetic acid. The p K a value of the carboxymethylene group at the 190 position was determined as 5.6 ± 0.4 by 13 C-NMR. On the basis of this value, the p K a of the carboxylate of Glu-190 of the TF 1 β subunit was estimated to be 6.8 ± 0.5. The unusually high p K a could play a role in the catalytic mechanism of F 1 -ATPase.