Measurement of sulfonation of 4-nitrophenol, catalyzed by cytosol from the human small intestine, showed an interesting variation in the rates over a wide substrate concentration range [33], as shown...

Measurement of sulfonation of 4-nitrophenol, catalyzed by cytosol from the human small intestine, showed an interesting variation in the rates over a wide substrate concentration range [33], as shown in Fig. 5. How would you explain the results shown?