Destroying the Trojan horse. Penicillin is hydrolyzed and thereby rendered inactive by penicillinase (also known as b-lactamase), an enzyme present...

18. Destroying the Trojan horse. Penicillin is hydrolyzed and thereby rendered inactive by penicillinase (also known as b-lactamase), an enzyme present in some penicillin-r esistant bacteria. The mass of this enzyme in Staphylococcus aureus is 29.6 kd. The amount of penicillin hydrolyzed in 1 minute in a 10-ml solution containing 1029 g of purified penicillinase was measured as a function of the concentration of penicillin. Assume that the concentration of penicillin does not change appreciably during the assay.

[Penicillin] Amount hydrolyzed mM (nmol) 1 0.11 3 0.25 5 0.34 10 0.45 30 0.58 50 0.61

(a) Plot V0 versus [S] and 1yV0 versus 1y[S] for these data. Does penicillinase appear to obey Michaelis-Menten k inetics? If so, what is the value of KM?

(b) What is the value of Vmax?

(c) What is the turnover number of penicillinase under these experimental conditions? Assume one active site per enzyme molecule.