Question

Q1)

A) True or False? Proximity and orientation effects are a feature of all enzyme-catalyzed reactions. Explain your reasoning.

B) PMSF (phenylmethylsulfonyl fluoride) is an inactivator of serine proteases. It is commonly used in the production of protein for experimental study; it prevents cellular proteases from digesting the protein of interest
True or false? Lowering the pH of the solution would alter binding by PMSF. In a single sentence, explain how you arrived at your answer.

Answer 1

A. Proximity and orientation have role in enzyme catalyzed reaction. It is sometimes referred to as "entropy reduction".

• Proximity: Reaction between bound molecules doesn't require an improbable collision of 2 molecules -- they're already in "contact" (increases the local concentration of reactants).
• Orientation: Reactants are not only near each other on enzyme, they're oriented in optimal position to react, so the improbability of colliding in correct orientation is taken care of.

Hence given statement is true.

B. In biochemistry, phenylmethane sulfonyl fluoride or phenylmethylsulfonyl fluoride (PMSF) is a serine protease inhibitor commonly used in the preparation of cell lysates. PMSF does not inhibit all serine proteases. It is rapidly degraded in water and stock solutions are usually made up in anhydrous ethanol, isopropanol, corn oil.

PMSF binds specifically to the active site serineresidue in a serine protease. It does not bind to any other serine residues in the protein. This is a result of the hyperactivity of that serine residue caused by the specific environmental conditions in the enzyme's active site. Because PMSF binds covalently to the enzyme, the complex can be viewed by X-ray crystallography; it can therefore be used as a chemical label to identify an essential active site serine in an enzyme.

Hence given statement is false.