Which chemical inhibitor is specific for the Bone isoenzyme?

• A. 3M Urea
• B. Levamisole
• C. Phenylalanine
• D. Leucine

Answer: (A)

Understanding how alkaline phosphatase isoenzymes respond to inhibitors helps identify which source is contributing to a change in activity. The bone isoenzyme can be selectively inhibited by a high concentration of urea, such as 3M, which reduces its activity more than other isoenzymes. This selective sensitivity provides a way to distinguish bone-derived ALP from others in a mixture, making 3M urea the best choice for targeting the bone isoenzyme.

Levamisole, on the other hand, inhibits the placental isoenzyme (and has little effect on bone), so it doesn’t specifically identify bone ALP. The amino acids phenylalanine and leucine do not offer reliable, selective inhibition of the bone isoenzyme in standard isoenzyme analyses, so they aren’t used for this purpose.