In kinetics experiments, the hydrolysis of the substrate sialic acid by neuraminidase appears to obey Michaelis–Menten kinetics. Neuraminidase activity is critical for viral infectivity; thus, this enzyme is the target of much work by pharmaceutical companies to develop a drug to treat influenza virus infection. The drug “Tamiflu” is a competitive inhibitor of neuraminidase. Initial rate data collected at pH = 6.15, 37 °C with 0.021 μM neuraminidase and 25.0 μM sialic acid gives a Lineweaver–Burk plot with a slope of 51.2 s. 

(a) Recall from Problem 23 that the k_cat for neuraminidase at pH = 6.15, 37 °C is 26.8 s^-1. Calculate K_M for the hydrolysis of sialic acid. 

(b) When the reactions in part (a) are repeated in the presence of 0.040 μM of Tamiflu, the slope of the Lineweaver–Burk plot is 198.8 s. Calculate the value of K_I for Tamiflu.