Figure 4.

Lon^VQ displays diminished ATPase and degradation activity compared with Lon^WT. (a) ATP hydrolysis activity of Lon^WT (dark gray bars) and Lon^VQ (light gray bars). At lower concentrations where Lon^WT is predominately hexameric, there is approximately 1.5‐fold higher activity for Lon^WT compared with Lon^VQ. However, at higher concentrations where both proteins are expected to be predominantly dodecamer, the ATP hydrolysis activity is comparable. The values reported are from three independent experiments performed in triplicate, and the error bars represent SEM. (b and c) Degradation of 40 μM ³⁵S‐titin^I27‐sul20 (b) and ³⁵S‐IbpB (c) by Lon^WT and Lon^VQ was monitored by generation of acid‐soluble radioactive peptides. The indicated Lon concentrations are in monomer equivalents. Degradation rates were normalized in comparison to the rate at 0.75 μM. Each experiment was performed in triplicate and error bars represent SEM (curved lines connecting data points do not represent statistically‐based fitting).