Theory 22/Protein function
Second Functions Need a Shift
The claim
An enzyme's secondary function appears when the ratio of secondary substrate to primary substrate concentration crosses a threshold, so moonlighting is a concentration phenomenon rather than a structural one.
01Mechanism
The active site catalyses both reactions with different efficiencies; the ratio of substrate concentrations determines which flux dominates.
02Predictions
- P1Secondary activity should appear above a concentration ratio.
- P2Structural similarity alone should mispredict.
03Refutation
Secondary activity independent of concentration would remove the competition.
04Why it resists the grid
One sequence, two functions, no way to assign the protein to a single functional category.