H. Peter Lu,Luying Xun,X. Sunney Xie ^*

Enzymatic turnovers of single cholesterol oxidase molecules were observed in real time by monitoring the emission from the enzyme's fluorescent active site, flavin adenine dinucleotide (FAD). Statistical analyses of single-molecule trajectories revealed a significant and slow fluctuation in the rate of cholesterol oxidation by FAD. The static disorder and dynamic disorder of reaction rates, which are essentially indistinguishable in ensemble-averaged experiments, were determined separately by the real-time single-molecule approach. A molecular memory phenomenon, in which an enzymatic turnover was not independent of its previous turnovers because of a slow fluctuation of protein conformation, was evidenced by spontaneous spectral fluctuation of FAD.

H. P. Lu and X. S. Xie, Pacific Northwest National Laboratory, William R. Wiley Environmental Molecular Sciences Laboratory, Richland, WA 99352, USA. L. Xun, Washington State University, Department of Microbiology, Pullman, WA 99164, USA.
^*   To whom correspondence should be addressed. E-mail: xsxie@pnl.gov

Volume 282, Number 5395 Issue of 4 Dec 1998, pp. 1877 - 1882 
©1998 by The American Association for the Advancement of Science.