In this article, we discuss single molecule observation of rotational catalysis by E. coli ATP synthase (F-ATPase) using small gold beads. Studies involving a low viscous drag probe showed the stochastic properties of the enzyme in alternating catalytically active and inhibited states. The importance of subunit interaction between the rotor and the stator, and thermodynamics of the catalysis are also discussed. Single Molecule Enzymology is a new trend for understanding enzyme mechanisms in biochemistry and physiology. (c) 2013 IUBMB Life, 65(3):247254, 2013