The lock and key model of enzymes suggests that the shape of the enzyme (the lock) is specifically complementary to the shape of its substrate (the key). Therefore, to determine the most likely substrate from the options given (a, b, c, d, e), you would need to know the structure and shape of the enzyme active site in relation to the potential substrates.
Since the specific shapes or structures of options a, b, c, d, and e are not provided in your question, I cannot definitively identify which one is the most likely substrate. Please provide more information about the shapes or characteristics of the options, and I can help determine which one is most compatible with the enzyme based on the lock and key model.