A reanalysis of the foundations of the macromolecular rate theory

Abstract

Abstract. The macromolecular rate theory (MMRT) has been proposed as a mechanistic scheme to describe the temperature dependence of enzymatic reactions, and has enjoyed quite some popularity recently. MMRT was motivated by assuming that enzyme denaturation is not sufficient to explain the decline of enzyme activity above an optimal temperature, and was derived with two experimental assumptions: (1) the half saturation parameter is independent of temperature; and (2) when the substrate concentration is kept at 10 times of the half saturation parameter at reference temperature, the enzyme assays are substrate saturated under all experimental temperatures. We show that both the motivating and experimental assumptions do not hold under many conditions. Consequently, the MMRT estimated temperature sensitivity of the maximum catalysis rate is inaccurate. It can mischaracterize temperature-related biochemical behaviors, such as inferring the existence of a unique optimal temperature where biochemical rate peaks, and the shift of this optimal temperature as an indicator of thermal acclimation or adaptation. We recommend that chemical kinetics theory is a better candidate for mechanistic modeling of the temperature dependence of biogeochemical rates.

Bridging 20 Years of Soil Organic Matter Frameworks: Empirical Support, Model Representation, and Next Steps

“…In particular, understanding of microbial response to temperature has been analyzed using the Macro-Molecular Rate Theory (MMRT) which indicated variability in microbial temperature sensitivity and acclimation (Alster et al, 2020;Moinet et al, 2020;Shipper et al, 2014). However, temporal dynamics and underlying mechanisms of microbial respiratory sensitivity to temperature remain uncertain, including specific assumptions of MMRT (Tang & Riley, 2023). Moisture control was similarly found to be strongest at extremes due to either lack of physical access to substrate or microbial desiccation in dry situations, or due to saturation creating a deficiency in oxygen, but with less clear effects at moderate moistures (Gabriel & Kellman, 2014;Sierra et al, 2016;Wang et al, 2016).…”