The catalytic power of magnesium chelatase: a benchmark for the AAA+ ATPases. Issue 12 (2nd June 2016) - Adams, Nathan B. P.
Abstract : In the first committed reaction of chlorophyll biosynthesis, magnesium chelatase couples ATP hydrolysis to the thermodynamically unfavorable Mg 2+ insertion into protoporphyrin IX (ΔG°′ of circa 25–33 kJ·mol −1 ). We explored the thermodynamic constraints on magnesium chelatase and demonstrate the effect of nucleotide hydrolysis on both the reaction kinetics and thermodynamics. The enzyme produces a significant rate enhancement ( k cat / k uncat of 400 × 10 6 m ) and a catalytic rate enhancement, k cat / K m DIX K 0.5 Mg k uncat, of 30 × 10 15 m −1, increasing to 300 × 10 15 m −1 with the activator protein Gun4. This is the first demonstration of the thermodynamic benefit of ATP hydrolysis in the AAA + family. Abstract :