RNA Polymerase II - Kinetics

Kinetics

Enzymes can catalyze up to several million reactions per second. Enzyme rates depend on solution conditions and substrate concentration. Like other enzymes POLR2 has a saturation curve and a maximum velocity (V_max). It has a K_m (substrate concentration required for one-half V_max) and a k_cat (the number of substrate molecules handled by one active site per second). The specificity constant is given by k_cat/K_m. The theoretical maximum for the specificity constant is the diffusion limit of about 108 to 109 (M−1 s−1), where every collision of the enzyme with its substrate results in catalysis.

The turnover number for RNA polymerase II is 0.16 s−1 subject to concentration. Bacterial RNA polymerase, a relative of RNA Polymerase II, switches between inactivated and activated states by translocating back and forth along the DNA. Concentrations of _eq = 10 μM GTP, 10 μM UTP, 5 μM ATP and 2.5 μM CTP, produce a mean elongation rate, turnover number, of ~1 bp (NTP)−1 for bacterial RNAP, a relative of RNA polymerase II.

RNA Polymerase II is inhibited by α-amanitin.