Question

Biochemists oftentimes mutate (change) amino acids in an enzyme in order to learn about their function in catalysis. When one particular Asp residue in Enzyme A was changed (mutated) to an Ala residue, Enzyme A was not able to carry out catalysis (i.e. it became inactive). The most reasonable explanation for this observation is that:

		This enzyme works through an acid-base mechanism
		This enzyme works through covalent catalysis
		Mutation to Ala allows this enzyme to bind metals.
		This enzyme was inactivated by a disulfide bond

Answer 1

A change in an amino acid leads to a change in the primary structure of the protein. A change in the tertiary structure means a change in the shape of the protein. If this change affects the active site of the enzyme, the activity of the enzyme will be affected. this enzyme acid-base catalysis is involved in a majority of enzymatic reactions, wherein the side chains of various amino acids act as general acids or general basis.

Aspartic acid is acidic while alanine is neutral in nature. Two amino acids have acidic side chains at neutral pH. These are aspartic acid or aspartate (Asp) and glutamic acid or glutamate (Glu). Their side chains have carboxylic acid groups whose pKa's are low enough to lose protons, becoming negatively charged in the process. The pH of an amino acid affects which atoms protonate and deprotonate. ... This is due to ammonium (amino) groups being less acidic than carboxylic acids.

Thus this enzyme works though acid-base mechanism.