A Background Enzymatic Active Bath Affects Liquid-Liquid Phase Separation of Proteins*

The cell interior is an active bath driven by a myriad of enzymes. It is an open problem as to how this background activity can affect physical processes in the cell including liquid-liquid phase separation. We seek to experimentally reconstitute a model system for an active bath of enzymes to determine the effects on the liquid phase separation of a model condensate protein. We will use urease, an exothermic and kinetically fast enzyme that converts urea to carbon dioxide and ammonia, as the background enzyme. We will use ubiquilin-2 (UBQLN2), a protein that phase separates when high salt is added. We have scanned both the salt concentration to form condensates, and the urea concentration to control urease activity and observed droplets using fluorescence microscopy. Preliminarily, we find that the enzyme activity increases both the number and size of the droplets of UBQLN2.