Abstract
The ars operon of plasmid R773 encodes an As(III)/ Sb(III) extrusion pump. The catalytic subunit, the ArsA ATPase, has two homologous halves, A1 and A2, each with a consensus nucleotide-binding sequence. ATP hydrolysis is slow in the absence of metalloid and is accelerated by metalloid binding. ArsA M446W has a single tryptophan adjacent to the A2 nucleotide-binding site. Tryptophan fluorescence increased upon addition of ATP, ADP, or a nonhydrolyzable ATP analogue. Mg2+ and Sb(III) produced rapid quenching of fluorescence with ADP, no quenching with a nonhydrolyzable analogue, and slow quenching with ATP. The results suggest that slow quenching with ATP reflects hydrolysis of ATP to ADP in the A2 nucleotide-binding site. In an A2 nucleotide-binding site mutant, nucleotides had no effect. In contrast, in an A1 nucleotide-binding mutant, nucleotides still increased fluorescence, but there was no quenching with Mg2+ and Sb(III). This suggests that the A2 site hydrolyzes ATP only when Sb(III) or As(III) is present and when the A1 nucleotide-binding domain is functional. These results support previous hypotheses in which only the A1 nucleotide-binding domain hydrolyzes ATP in the absence of activator (unisite catalysis), and both the A1 and A2 sites hydrolyze ATP when activated (multisite catalysis).
Original language | English (US) |
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Pages (from-to) | 23815-23820 |
Number of pages | 6 |
Journal | Journal of Biological Chemistry |
Volume | 277 |
Issue number | 26 |
DOIs | |
State | Published - Jun 28 2002 |
Externally published | Yes |
ASJC Scopus subject areas
- Biochemistry
- Molecular Biology
- Cell Biology