Lactase is enzyme composed of a polypeptide hydrolyzes the disaccharide lactose to produce monarchies. the optimal ph for lactase activity is 6. transfer of lactase to ph 5 results in a substantial decrease in enzyme activity, likely due to the disruption of 1) only the primary structure of the enzyme. 2) the secondary and tertiary structure of the enzyme. 3) the primary and secondary structure of the enzyme. 4) the secondary, tertiary, and quaternary structure of the enzyme.