Passage The Recent Advent of Multidrug-Resistant Mycobacterium Tuberculosis (Mtb) Has Led

Passage
The recent advent of multidrug-resistant Mycobacterium tuberculosis (Mtb) has led to the search for novel agents to combat tuberculosis.  Mtb secretes over 70 serine proteases that may be used as viable drug targets.  Hydrolase important for pathogenesis 1 (Hip1) is a serine protease found in Mtb with proteolytic activity that is required for dampening the host inflammatory response.  Given the role of Hip1 in Mtb virulence, analyzing Hip1 substrate specificity is a critical step in designing selective inhibitors for effective tuberculosis treatment.Fluorogenic substrates are nonfluorescent compounds that release a fluorescent reporter group when acted upon by an enzyme.  Such substrates are useful biomolecular imaging tools that allow monitoring of enzymatic activity in vitro and in vivo.  A large library of peptides was screened against Hip1, and enzymatic cleavage was analyzed using mass spectrometry to facilitate the design of fluorogenic substrates (Figure 1) .
Figure 1  Schematic design of Hip1 fluorogenic substrates.  P1, P2, P3, and P4 in Group 1 represent the positions of variable amino acids in the peptide.  Group 2 depicts the fluorescent compound released on Hip1 cleavage.Researchers reported Michaelis-Menten kinetic parameters for substrates from two peptide families: the WKLL substrates and the CSL substrates.Table 1  Kinetic Parameters of Fluorogenic Substrates for Mtb Hip1
Adapted from Lentz CS, Ordonez AA, Kasperkiewicz P, et al. Design of Selective Substrates and Activity-Based Probes for Hydrolase Important for Pathogenesis 1 (HIP1) from Mycobacterium tuberculosis. ACS Infect Dis. 2016;2(11) :807-815.
-The CSL substrates from Table 1 were tested in vitro at saturating substrate concentration in solutions containing 10 pM or 100 pM Hip1 enzyme.  The relative fluorescence of these substrates was then measured.  Which of the following graphs best reflects the expected results?

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