Which chemical inhibitor inhibits Placental, Intestinal, Regan, and Nagao isoenzymes?

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

Answer: (C)

In alkaline phosphatase isoenzyme analysis, inhibitors are used to see how different forms of the enzyme respond, which helps identify which isoenzymes are present. Phenylalanine acts as a competitive inhibitor that can suppress activity across multiple ALP isoforms. Placental and intestinal forms are strongly affected by phenylalanine, and in many assay conditions the tumor-associated Regan and Nagao isoenzymes also show sensitivity to phenylalanine. Because a single inhibitor that broadly reduces activity across all four isoenzymes is most useful in differentiating and identifying them, phenylalanine is the best choice here.

Other inhibitors tend to have more limited or selective effects on the isoenzymes, so they wouldn’t reliably suppress all four in this context. This makes phenylalanine the most appropriate option for inhibiting placental, intestinal, Regan, and Nagao isoenzymes.