Question

Enzyme X has a primary structure made up of 130 amino acids. In tertiary structure amino acids numbers 56, 58, 81-84, and 91-95 form the active site. Reactants Amino acids "unknown molecule" binds to on enzyme tertiary structure Activity of enzyme (1 μmolmin−1) Enzyme + substrate Not applicable 31.8 Enzyme + substrate + unknown molecule A 83-84, 92-94 11.4 Enzyme + substrate + unknown molecule B 41-47 31.9 Enzyme + substrate + unknown molecule C 97-99, 109 6.2 Looking at the data above, determine the category of molecule of unknown A, B, and C: 1) A = cofactor B = non-competitive inhibitorC= non-competitive inhibitor 2) A = competitive inhibitorB = not a cofactorC= non-competitive inhibitor 3) A = not a cofactorB = competitive inhibitorC= non-competitive inhibitor 4) A = non-competitive inhibitorB = non-competitive inhibitorC= competitive inhibitor 5) A = competitive inhibitorB = non-competitive inhibitorC= non-competitive inhibitor 1. Does it inhibit the enzyme? A and C do, so they’re inhibitors. B does not inhibit the enzyme, so it can’t be called an inhibitor (even if you didn’t remember what cofactors are, the fact that it has no effect on the activity of the enzyme tells you that it’s not an inhibitor of any kind) 2. What kind of inhibitor is it? To answer that, answer - does it bind at the active site? If it binds at the active site (A does), it’s a competitive inhibitor. If it doesn’t (C), it’s a non-competitive inhibitor.

Answer 1

Question:

The question is unclear but I think I found it elsewhere and have rewritten it below:

Enzyme X has a primary structure made up of 130 amino acids. In tertiary structure amino acids numbers 56, 58, 81-84, and 91-95 form the active site.

Looking at the data in the attached table, determine the category of unknown molecules A, B and C.

1) A = cofactor B = non-competitive inhibitor C= non-competitive inhibitor

2) A = competitive inhibitor B = not a cofactor C= non-competitive inhibitor

3) A = not a cofactor B = competitive inhibitor C= non-competitive inhibitor

4) A = non-competitive inhibitor B = non-competitive inhibitor C= competitive inhibitor

5) A = competitive inhibitor B = non-competitive inhibitor C= non-competitive inhibitor

Answer:

2) A = competitive inhibitor B = not a cofactor C= non-competitive inhibitor

Explanation:

A competitive inhibitor is a molecule that binds to the active site of an enzyme, directly blocking its ability to catalyse reactions and thus inhibiting its activity. A non-competitive inhibitor inhibits the activity of an enzyme, but not through binding an active site. A co-factor is an accessory protein that influences and promotes the activity of the enzyme

The table shows that unknown molecule A binds to the active site (based on the amino acid positions at which it binds) and reduces the activity of the enzyme (from 31.8 - 11.4) - a competitive inhibitor

Unknown molecule B does not bind at the active site, and has no affect on the activity of the enzyme - not a co-factor or an inhibitor

Unknown molecule C does not bind to the active site, but strongly reduces the activity of the enzyme - a non-competitive inhibitor