Nitrogenase Catalytic Cycle — 2D Reaction Wheel

Catalytic Drive

Electron flux (ATP turnover rate) 1.0×

N₂ partial pressure 0.8 atm

Turnover Totals

NH₃ produced

H₂ released

ATP hydrolyzed

Active sites

150 / 150

How it works

This is the same Lowe-Thorneley kinetic scheme as the 3D docking simulator, but drawn the way biochemists actually diagram it: as a circular reaction-coordinate wheel, not a protein dock/undock animation. Each catalytic site is a dot that orbits the wheel through eight electron-accumulation stations E0 → E7, closing the loop through a resolving arc at E8:

N2 + 8 H+ + 8 e- + 16 MgATP + 16 H2O
   -> 2 NH3 + H2 + 16 MgADP + 16 Pi

fluxTerm = flux / (flux + K),  K = 0.6
P(N2 fixed | E8 reached) = fluxTerm × [N2 atm]

Reaction wheel (left) — every dot's angular position is its live progress through the 8-electron cycle; dwell time per station is cycleTime/8 with cycleTime = 1.2/flux, identical to the population field in the 3D version. Color still ramps blue (E0) → gold (E7); gray dots have been permanently knocked out by O₂.
E-state histogram (top right) — a live bar count of how many sites currently sit in each of the 8 states, the same distribution the wheel encodes spatially, read as a quantitative population snapshot.
Production-rate strip chart (bottom right) — a scrolling trace of NH₃ and H₂ output rate (molecules/s across the population), sampled every 0.25s from the same discrete turnover events driving the wheel — a real derivative of the cumulative totals, not a decorative animation.
Electron flux / N₂ pressure sliders and O₂ exposure — identical meaning and identical formulas to the 3D model: higher flux both speeds the cycle and biases the E8 branch toward productive N₂ reduction; low N₂ or low flux defaults sites to unproductive H₂ evolution (4 H₂ per turnover instead of 1 NH₂+1 H₂); O₂ exposure inactivates active sites at random with the same 6%·dt per-frame hazard, irreversibly.

Real-world relevance: nitrogenase is the only enzyme family that breaks the N≡N triple bond at ambient temperature and pressure, and its obligate 1 H₂-per-N₂ waste and extreme O₂ sensitivity are exactly the two properties this reaction wheel is built to make legible at a glance.

E0 — resting site E7 — fully loaded site NH₃ (productive turnover) O₂-inactivated site