Kagawa, A. | Search bioRxiv

bioRxiv2020

Hyperactivation of L-lactate oxidase by liquid-liquid phase separation

Liquid droplets formed by liquid-liquid phase separation are attracting attention as functional states of proteins in living cells. Liquid droplets are thought to activate enzymatic reactions by assembling the required molecules. Thus, liquid droplets usually increase the affinity of an enzyme to its substrates, leading to decreased KM values. In this study, we demonstrate a new mechanism of enzyme activation in the droplets using Llactate oxidase (LOX). In the presence of poly-L-lysine (PLL), LOX formed droplets with diameters of hundreds of nanometers to tens of micrometers, stabilized by electro-static interaction. The enzyme activity of LOX in the droplets was significantly enhanced by a fourfold decrease in KM and a tenfold increase in kcat. To our knowledge, this represents the first report for increasing kcat by the formation of the liquid droplet. Interestingly, the conformation of LOX changed in the liquid droplet, probably leading to increased kcat value. Understanding enzyme activation in the droplets provides essential information about enzyme function in living cells in addition to biotechnology applications.

biochemistry↗

bioRxiv2020

Foliar water uptake as a source of hydrogen and oxygen in plant biomass

Introductory biology lessons around the world typically teach that plants absorb water through their roots, but, unfortunately, absorption of water through leaves and subsequent transport and use of this water for biomass formation remains a field limited mostly to specialists. Recent studies have identified foliar water uptake as a significant but still unquantified net water source for terrestrial plants. The growing interest in the development of a new model that includes foliar uptake of liquid water to explain hydrogen and oxygen isotope ratios in leaf water and tree rings requires a method for distinguishing between these two water sources. I therefore devised a method utilizing two different heavy waters (HDO and H218O) to simultaneously label both foliar-uptake water and root-uptake water and quantify their relative contributions to plant biomass. Using this new method, I here present evidence that, in the case of well-watered Cryptomeria japonica, hydrogen and oxygen incorporated into new leaf cellulose in the rainy season derives mostly from foliar-uptake water, while that of new root cellulose derives mostly from root-uptake water, and new branch xylem is somewhere in between. Abandoning the assumption that these elements are supplied from soil water alone may have vast implications in fields ranging from isotope dendroclimatology, silviculture, to biogeochemistry.

plant biology↗