How does mercury chloride inhibit catechol oxidase?

Question

How does mercury chloride inhibit catechol oxidase?

Answer 1

Catechol oxidase is an enzyme, but more importantly a PROTEIN.

For a protein to function properly---and especially one with catalytic activity that is responsible for converting a substrate chemical to a product chemical---certain FUNCTIONAL GROUPS such as imidazoles, carboxylates, amines, guanidinylates, and especially thiols (-SH groups) must be present as part of the important amino acids that make up the protein and are responsible for its function.

Mercury salts (the Hg[2+] ion) are well known to associate with THIOL groups of any kind.  Some of these thiols are present in the active site of the enzyme and are vital to its function.  What probably happens is that the mercuric ion enters the active site and IRREVERSIBLY binds to an important thiol that must be essential to function, and thus inhibits, preventing the substrate from being converted to product.  Or it might be a REVERSIBLE inhibition, but the presence of mercuric ion is so high that it effectively locks out the substrate from binding.  To prove it is reversible, dialyze the oxidase in a buffer containing no mercuric salt to remove it, and see if function is restored.  If not, the mercuric ion bound to the thiol irreversibly and inactivated the enzyme.

The key here is to understanding what chemical groups the inhibitor binds to.

Answer 2

fdf