Biochemistry

Distinctive Individualism

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Science  04 Apr 2008:
Vol. 320, Issue 5872, pp. 23
DOI: 10.1126/science.320.5872.23b

Single-molecule studies have shown that enzyme activities can differ substantially from the average measured in ensemble experiments and that rates of a single enzyme can vary because of conformational fluctuations. Most experiments, however, have not looked at a large enough number of molecules to characterize the stochastic nature of enzyme kinetics. Rissin et al. use an array of 50,000 40-fl reaction chambers in which most chambers were empty but approximately 5% contained a single molecule of β-galactosidase. Hydrolysis of a nonfluorescent substrate to a fluorescent product was monitored simultaneously for about 200 enzyme molecules. Averaged single-molecule turnover velocities agreed well with bulk measures, but there was a wide distribution in activities, confirming the heterogeneity within enzyme populations observed previously. The variability in rate was independent of substrate concentration, suggesting that it arises from variability in kcat. The effect of enzyme activity distribution on metabolic pathways remains to be determined. — VV

J. Am. Chem. Soc. 130, 10.1021/ja711414f (2008).

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