In the presence of PEG20k, upon adding ATP, a transient increase in turbidity occurred, followed by a gradual return of turbidity to the baseline (Fig. and Supplementary Fig. ). To investigate the reversible droplet formation of YK13-sfGFP within cells, we added a glycolysis inhibitor, 2-deoxyglucose (2-DOG), which decreases the intracellular ATP level . The addition of 10 mM 2-DOG resulted in dissolution of most droplets in about 20 min, supporting the assertion that ATP acts as a counter-anion of YK13 peptide in living cells (Fig. and Supplementary Fig. ).