Question

You test enzyme E activity on a large protein substrate. This substrate is not cleaved by enzyme E. You then treat the substrate with DTT (a compound that disrupts disulfide bonds) and test the enzyme E activity again. This time the substrate is cleaved by enzyme E. Why was enzyme E able to cleave the protein substrate only after the substrate was treated with DTT?

Accepted Answer

Enzyme E binds and cuts at specific sites. These sites are not present on the exterior of the substrate when the substrate is properly folded. When the disulfide bonds within the substrate protein are disrupted, the 3 dimensional shape is altered, and the protein unfolds. This allows enzyme E access to sites that were previously protected within the substrate protein.

Front	You test enzyme E activity on a large protein substrate. This substrate is not cleaved by enzyme E. You then treat the substrate with DTT (a compound that disrupts disulfide bonds) and test the enzyme E activity again. This time the substrate is cleaved by enzyme E. Why was enzyme E able to cleave the protein substrate only after the substrate was treated with DTT?
Back	Enzyme E binds and cuts at specific sites. These sites are not present on the exterior of the substrate when the substrate is properly folded. When the disulfide bonds within the substrate protein are disrupted, the 3 dimensional shape is altered, and the protein unfolds. This allows enzyme E access to sites that were previously protected within the substrate protein.

Substrate Enzyme E Protein Sites Test Activity Cleaved