The stimulation of coupling factor 1 ATPase by tentoxin

Area of Science:

• Biochemistry
• Plant Physiology
• Photosynthesis

Background:

• Coupling factor 1 (CF1) is a key enzyme in ATP synthesis during photosynthesis.
• CF1 activity is regulated by various factors, including divalent cations like Ca2+.
• Tentoxin is a cyclic tetrapeptide known to affect plant physiology.

Purpose of the Study:

• To investigate the effect of tentoxin on the Ca2+-dependent ATPase activity of coupling factor 1.
• To determine the kinetic parameters of tentoxin's interaction with CF1.
• To assess the impact of tentoxin on coupled electron transport.

Main Methods:

• Enzyme kinetics assays were performed to measure CF1 ATPase activity.
• The effect of varying tentoxin concentrations on enzyme kinetics was analyzed.
• Measurements of coupled electron transport rates were conducted under different tentoxin concentrations.

Main Results:

• Tentoxin (10–1000 µM) significantly stimulated species-selective Ca2+-dependent ATPase activity of CF1.
• Tentoxin decreased the Km for ATP to approximately 0.3 mM and increased Vmax 2.75-fold.
• Concentrations of tentoxin above 1.6 µM reduced coupled electron transport to basal levels without uncoupling.

Conclusions:

• Tentoxin acts as a potent activator of CF1 Ca2+-dependent ATPase activity in a species-specific manner.
• The activation involves altered affinity for ATP and increased catalytic rate.
• Tentoxin inhibits photosynthesis by reducing electron transport, independent of uncoupling effects.