SIRT5 has emerged as a critical player in maintaining cardiac health and neuronal viability upon stress and functions as a tumour suppressor in a context-specific manner...We have, for the first time, identified a SIRT5-selective allosteric activator, nicotinamide riboside (NR). It can increase SIRT5 catalytic efficiency with different synthetic peptide substrates. The mechanism of action was further explored using a combination of molecular biology and biochemical strategies. Based on the existing structural biology information, the NR binding site was also mapped out.