Avian brain plasticity evident during song learning

ers to understand an enzyme’s mode of action, enabling observation of transient intermediates, conformational changes, and the determination of rate constants. Such information can be difficult to obtain because Brownian motion prevents solution-phase molecules from staying still for the length of time required to make meaningful measurements, and immobilization can alter an enzyme’s biochemical properties. Randall Goldsmith et al. (pp. 17269– 17274) circumvented this obstacle by describing a way to immobilize a single enzyme without altering the enzyme’s activity. The authors used a microfluidic trapping device called the Anti-Brownian Electrokinetic (ABEL) trap to effectively immobilize an enzyme while keeping it in solution, enabling prolonged solutionphase measurements of enzymatic activity. The device tracks Brownian motion of single molecules and applies an electric field to the solution to counteract Brownian-induced displacements. When the authors applied the tool to study nitrite reductase, a copper-containing enzyme found in plants and bacteria that reduces nitrite to nitric oxide, they observed discrete oxidation and reduction states of the enzyme’s catalytic site, and determined the rate constants for catalysis. According to the authors, the findings may help to resolve conflicting proposals of nitrite reductase’s mechanism, and the strategy could prove useful for future solution-phase, single-enzyme studies. — N.Z. October 18, 2011 u vol. 108 u no. 42 u 17237–17570