(ii) ATPase assay (PK/LDH).

ATP hydrolysis was measured with the enzyme-linked assay using pyruvate kinase and lactic dehydrogenase (PK/LDH). Two micrograms of pure ClpC1 or ClpX and a 10× molar excess of SSB (where indicated) were mixed with 100 μl of assay buffer B containing 1 mM phosphoenolpyruvate (Sigma catalog no. 860077), 1 mM NADH (Sigma catalog no. N8129), 2 U of pyruvate kinase-lactic dehydrogenase, 4 mM MgCl₂, and 1 mM ATP, and the ATPase activity was followed by measuring the oxidization of NADH to NAD spectrometrically at 340 nm. Measurements were performed in triplicate, which agreed within 5%.