Effects of molecular confinement and crowding on horseradish peroxidase kinetics using a nanofluidic gradient mixer

Journal Article · Tue Jan 12 00:00:00 EST 2016 · Lab on a chip (Print)

DOI:https://doi.org/10.1039/c5lc01413a· OSTI ID:1371712

Wichert, William R. A. ^[1]; Han, Donghoon ^[2]; Bohn, Paul W. ^[3]

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1. Univ. of Notre Dame, IN (United States). Dept. of Chemistry and Biochemistry
2. Univ. of Notre Dame, IN (United States). Dept. of Chemical and Biomolecular Engineering
3. Univ. of Notre Dame, IN (United States). Dept. of Chemistry and Biochemistry and Dept. of Chemical and Biomolecular Engineering

Here, we studied the effects of molecular confinement and crowding on enzyme kinetics at length scales and under conditions similar to those found in biological cells. These experiments were carried out using a nanofluidic network of channels constituting a nanofluidic gradient mixer, providing the basis for measuring multiple experimental conditions simultaneously. Furthermore, the 100 nm × 40 μm nanochannels were wet etched directly into borosilicate glass, then annealed and characterized with fluorescein emission prior to kinetic measurements. The nanofluidic gradient mixer was then used to measure the kinetics of the conversion of the horseradish peroxidase (HRP)-catalyzed conversion of non-fluorescent Amplex Red (AR) to the fluorescent product resorufin in the presence of hydrogen peroxide (H₂O₂). The design of the gradient mixer allows reaction kinetics to be studied under multiple (five) unique solution compositions in a single experiment. In order to characterize the efficiency of the device the effects of confinement on HRP-catalyzed AR conversion kinetics were studied by varying the starting ratio of AR : H₂O₂. Equimolar concentrations of Amplex Red and H₂O₂ yielded the highest reaction rates followed by 2 : 1, 1 : 2, 5 : 1, and finally 1 : 5 [AR] : [H₂O₂]. Under all conditions, initial reaction velocities were decreased by excess H₂O₂. Crowding effects on kinetics were studied by increasing solution viscosity in the nanochannels in the range 1.0–1.6 cP with sucrose. Increasing the solution viscosities in these confined geometries decreases the initial reaction velocity at the highest concentration from 3.79 μM min^-1 at 1.00 cP to 0.192 μM min^-1 at 1.59 cP. Variations in reaction velocity are interpreted in the context of models for HRP catalysis and for molecular crowding.

• Research Organization: University of Notre Dame, IN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: AC05-00OR22725; FG02-07ER15851
• OSTI ID: 1371712
• Journal Information: Lab on a chip (Print), Vol. 16, Issue 5; ISSN 1473-0197
• Publisher: Royal Society of Chemistry
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY