ATP Synthesis by the F0F1-ATPase from the Thermophilic Bacillus PS3 Co-reconstituted with Bacteriorhodopsin into Liposomes: EVIDENCE FOR STIMULATION OF ATP SYNTHESIS BY ATP BOUND TO A NONCATALYTIC BINDING SITE

Peter Richard,Bruno Pitard,Jean-Louis Rigaud

doi:10.1074/jbc.270.37.21571

Peter Richard, Bruno Pitard + Show 1 more

Open Access

https://doi.org/10.1074/jbc.270.37.21571

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Abstract

F-type ATPase from the thermophilic Bacillus PS3, TF0F1, which was essentially free of bound nucleotides after isolation and purification, was co-reconstituted into liposomes with the light-driven proton pump bacteriorhodopsin. The time course of the light-induced ATP synthesis was biphasic; an initial slow phase accelerated to a final steady-state rate two to three times faster. Adding ATP before initiating the reaction suppressed the slow phase, suggesting that the state of occupancy of specific sites by ATP regulated the synthetic activity of TF0F1. Incubating the purified TF0F1 with ADP and ATP revealed one ADP and two ATP binding sites that were stable to gel filtration. We analyzed the time courses of light-induced ATP synthesis for the enzyme with different nucleotide content, after co-reconstitution into liposomes with bacteriorhodopsin. The two ATP sites were identified to have regulatory function. A complex containing TF0F1.ADP, 1:1, was co-reconstituted with various quantities of ATP to obtain a range of molar ratios of TF0F1.ADP:ATP of between 1:0 and 1:1.7. It was found that the initial rate of ATP synthesis increased with the level of ATP bound to the enzyme. After binding one ATP, a stimulation of ATP synthesis by a factor of 2 was observed. The second ATP site also exhibited regulatory properties. It stimulated ATP synthesis but to a much smaller extent; the stimulation did not exceed 20%. Binding of the photoreactive analogues 2-azido-[alpha-32P]ADP and 2-azido-[alpha-32P]ATP to the TF0F1 and their effects on the rate of ATP synthesis are described further.(ABSTRACT TRUNCATED AT 250 WORDS)

Highlights

F-type ATPase from the thermophilic Bacillus PS3, TF0F1, which was essentially free of bound nucleotides after isolation and purification, was co-reconstituted into liposomes with the light-driven proton pump bacteriorhodopsin
The studies described in this paper represent an effort to understand the mechanisms and the complex patterns of nucleotide binding on F-type ATPase involved during ATP synthesis
The most interesting finding emerging from this report is that ATP synthesis by the F-type ATPase from the thermophilic Bacillus PS3 is shown to be significantly accelerated upon ATP binding to the protein

Summary

EXPERIMENTAL PROCEDURES

Chemicals—Purified egg yolk phosphatidylcholine was isolated according to the method of Singleton et al [22]. Analysis of Enzyme-bound Nucleotides—Binding of adenine nucleotides to TF0F1 was done following incubation of the protein (2–3 mg/ml) for 15 min at 40 °C in a buffer containing 50 mM K2SO4, 50 mM Na2SO4, 1 mM MgSO4, 25 mM KH2PO4 (pH 7.3), 5 mg/ml Triton X-100, and the indicated amounts of nucleotide. Light-induced ATP Synthesis—After detergent removal, the proteoliposomes were diluted in the same buffer used for their preparation and supplemented with 2 mM ADP or 2 mM Mg2ϩ. This mixture was incubated at 40 °C and preilluminated for 15 min. At intervals the optical density of the mixture was measured at 340 nm

RESULTS

First we determined the nucleotide content of our purified

Control without nucleotides ϩ UV

DISCUSSION