Q. A 55-year-old man presents to the clinic with chronic joint pain. After multiple tests, he is diagnosed with rheumatoid arthritis. His rheumatologist starts him on a new medication. A month later, he returns to the clinic for a follow-up. The patient reports some reduction in his joint pain, but it's still persistent. In an attempt to educate the patient about his medication, his rheumatologist uses a diagram. The diagram contains two lines: one representing the function of the enzyme in the absence of the medication (orange, normal), and the second representing the function of the enzyme in the presence of the medication (purple, non-competitive inhibitor). Based on the information given in the vignette, which of the following could be a likely mechanism of action for the patient's new medication?