A) TLQP-21 potentiates lipolysis induced by the β-adrenergic receptor agonist isoproterenol (ISO) (F(5,65)=62.1, p<0.0001). B) Unlike TLQP-21, the R21A mutant peptide does not potentiate isoproterenol-induced lipolysis in 3T3L1 adipocytes (F(5,65)=33.4, p<0.00001). C) Refocused INEPT spectra of R21A mutant, labeled with 13C and 15N at A16-L17-P18 with resonance assignments indicated. Experiments were performed in buffer (left panel) or in the presence of 3T3L1 cells (right panel). *p<0.05, ** p<0.001.