Electric Field Speeds Up Enzyme Reactions

Electrostatic fields in enzymes play a leading role not just in getting substrates to bind, but in the rate of the catalytic process itself, report Stephen D. Fried, Sayan Bagchi, and Steven G. Boxer of Stanford University (Science 2014, DOI: 10.1126/science.1259802). Whether or how such electric fields directly influence reactions has been controversial. Fried, Bagchi, and Boxer studied ketosteroid isomerase, which participates in steroid biosynthesis and degradation by relocating a C=C bond. The enzyme has one of the highest known unimolecular rate constants in biochemistry. The researchers used vibrational Stark effect spectroscopy to measure changes in an inhibitor’s vibrational energy levels induced by the enzyme’s electric field. They found that the enzyme exerts a strong electric field on a key C=O group involved in the enzyme’s rate-determining step and that the magnitude of the field correlates with the catalytic rate enhancement. The team estimates that about 70% of the enzyme’s ability to speed up isomerization ultimately comes from the electric field effect, whereas the remainder comes from positioning a basic protein residue to abstract a substrate proton. “The electric field could be a useful design criterion in the ongoing efforts to engineer enzymes with unnatural or enhanced functions,” the researchers write.