A qualitative quantum rate model for hydrogen transfer in soybean lipoxygenase

TL;DR

This paper presents a qualitative quantum rate model for hydrogen transfer in soybean lipoxygenase, capturing enzyme effects and reproducing kinetic isotope effect data across mutants and temperatures.

Contribution

The model introduces a minimal-parameter quantum approach incorporating enzyme gating to explain hydrogen transfer kinetics and isotope effects.

Findings

Successfully reproduces KIE data for SLO mutants

Highlights the role of gating frequency and donor-acceptor distance

Can be adapted to other enzymes with specific parameters

Abstract

The hydrogen transfer reaction catalysed by soybean lipoxygenase (SLO) has been the focus of intense study following observations of a high kinetic isotope effect (KIE). Today high KIEs are generally thought to indicate departure from classical rate theory and are seen as a strong signature of tunnelling of the transferring particle, hydrogen or one of its isotopes, through the reaction energy barrier. In this paper we build a qualitative quantum rate model with few free parameters that describes the dynamics of the transferring particle when it is exposed to energetic potentials exerted by the donor and the acceptor. The enzyme's impact on the dynamics is modelled by an additional energetic term, an oscillatory contribution known as "gating". By varying two key parameters, the gating frequency and the mean donor-acceptor separation, the model is able to reproduce well the KIE data for SLO wild-type and a variety of SLO mutants over the experimentally accessible temperature range. While SLO-specific constants have been considered here, it is possible to adapt these for other enzymes.