For a saturable enzyme with Vmax = 1200 mg/h, Km = 6 mg/L, and S = 3 mg/L, what is CLint and how does it compare to the maximal CLint at low substrate (S→0)?

• A. CLint = 133.3 L/h; Maximal CLint at low S is 200 L/h; CLint is lower at S = 3 mg/L
• B. CLint = 200 L/h; Maximal CLint at low S is 133.3 L/h; CLint is higher at S = 3 mg/L
• C. CLint = 100 L/h; Maximal CLint at low S is 600 L/h; CLint is lower
• D. CLint = 133.3 L/h; Maximal CLint at low S is 300 L/h; CLint is higher

Answer: (A)

For a saturable enzyme, the rate follows Michaelis-Menten: v = (Vmax × S)/(Km + S). Intrinsic clearance at a given substrate level is CLint = v/S, which simplifies to CLint = Vmax/(Km + S). The maximal CLint occurs as S approaches zero and equals Vmax/Km.

Plugging in the values: CLint = 1200 / (6 + 3) = 1200 / 9 = 133.3 L/h. The maximal CLint at very low substrate is 1200 / 6 = 200 L/h.

So CLint at S = 3 mg/L is lower (133.3 L/h) than the maximal CLint at low substrate (200 L/h).