ATP Synthase: The World’s Smallest Motor
Adenosine triphosphate (ATP) is a coenzyme produced in cellular mitochondria and is not only integral to cellular metabolism but also to life. The mitochondrial production of ATP, which occurs through a complex process called oxidative phosphorylation, has been determined to rely heavily on the enzyme ATP synthase. This determination was the result of a complex experiment that attempted to prove not only that ATP synthase was responsible for production of ATP but also the mechanism of that production as well. ATP synthase is a multisubunit complex with four main parts, each made up of multiple polypeptides (Reece and Campbell 2009). One of those subunits, F1, has been found to ‘function as a rotary molecular motor’ (Itoh et al. 2004). Also known as F1-ATPase, the F1 unit is attached to the F0 unit, an integral membrane protein with the subunit structure a,b2,c12 – the c subunits forming a circular array with a proton channel formed between the a and c subunits (Meisenberg and Simmons 2006). The ATP synthase motor turns in a clockwise rotation resulting in the hydrolysis of ATP to ADP. In the Itoh et al (‘Itoh’) experiment ATP was shown to be produced as a result of counterclockwise rotation of ATP synthase. Because ATP synthase turns clockwise in nature, the investigators developed a way to rotate the motor counterclockwise by way of attaching a small magnetic bead to the motor. The F1 subcomplex was attached to a glass surface with histidine residues. The protein Streptavidin, which has a high affinity for biotin, was then used to coat the magnetic bead. The γ-subunit of ATP synthase was then biotinylated so it would bind to the Streptavidin-coated magnetic bead which could now be rotated (counterclockwise) with magnets. To determine if the counterclockwise rotation of ATP synthase resulted in the production of ATP, the luciferin-luciferase reaction was used. Luciferase catalyzes a reaction between ATP and...
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