Question

The compound shown below inhibits an archaebacterial proteasome, binding to each of its active sites, which (unlike those of eukaryotic proteasomes) are all identical. What can you conclude about the substrate specificity of the archaebacterial proteasome?

Short answer

Only amino acids with hydrophobic residues are of interest to the proteasome.

Step-by-step solution

Substrate specificity.

The ability of an enzyme, such as a proteasome to bind only specific functional groups to its binding site is known as substrate specificity.

By binding to theproteasome's active site, the substance in question inhibits it.

Only certain amino acid residues bind to the active site of the proteasome.

Conclusion of the substrate specificity

The active site of proteasomes binds to certain amino acid residues. Hence finding amino acids in a given substance is required to deduce anything about the substrate specificity of a given proteasome.

The inhibitor has two leucine residues, indicating that the archaebacterialproteosome's active site is selective for hydrophobic residues such as leucine, and it cleaves the polypeptide chains following the hydrophobic residues.

Hence, the proteasome is only interested in amino acids with hydrophobic residues.