Question

Explain how an organic solvent like hexane could inhibit enzyme action. . Explain how addition of base could inhibit enzyme action.

Answer 1

Ans. 1. Enzymes are catalytic heteropolymers of amino acids. They are composed of 20 standard amino acids.

Addition of organic solvents like hexane may inhibit enzyme action in one or more of the following ways-

1. Denaturation of enzyme: The organic solvents (non-polar) may interact with the non-polar residues (= amino acids) in the enzyme and cause its denaturation by disrupting the normal 3D conformation of the enzyme molecule. Denaturation of enzyme causes loss of activity.

2. Interfere with active site or/ and allosteric site: The hydrophobic (non-polar) residues at active site/ binding site/ allosteric site may also exhibit affinity for the hydrophobic organic solvent molecules. The hydrophobic interaction among solvent molecules and amino acid residues may interfere with substrate binding, conformational-change mechanism, mechanism of catalysis, etc. and cause reduction/ loss of enzyme activity.

Ans. 2. Inhibition of enzyme activity by bases

Most of the enzyme exhibit optimum catalysis in a narrow pH range. The acidic and basic residues are most affected by pH change as it can cause the side chain to adopt positively- charged, negatively-charged or neutral forms.

1. Several enzymes use acid-base catalysis mechanism during catalysis in which one or more protons are exchange between substrate and residues at the active site. Alteration in pH (alkaline) may cause alteration in charge of the side chain of catalytic residues, which further causes inhibition of catalysis.

2. Bases may also cause change in the apparent charges on the residues outside the active site. The normal conformational change occurring in an enzyme molecule during catalysis, is transmitted through the amino acid residues from active site to rest of the molecule. However, change in pH may interfere with the transmission of conformation change through the molecule during catalysis and inhibit enzyme activity.