Activity of leucine aminopeptidase of Telchin licus licus: an important insect pest of sugarcane.

The enzymatic activity of leucine aminopeptidase (EC 3.4.11.1) from the intestinal tract of sugarcane giant borer (Telchin licus licus) was assayed by using a simple and sensitive spectrophotometric assay that uses L-leucyl-2naphthylamide as substrate. In this assay, L-leucyl-2-naphthylamide is hydrolyzed to produce 2-naphthylamine and Lleucine. The product 2-naphthylamine reacts with Fast Black K and can be monitored using a continuous spectrophotometric measurement at 590 nm. The data on the kinetic parameters indicates that the Km for the L-leucyl-2naphthylamide at pH 7.0 was found to be lower than those found for other LAP substrates. The Km and Vmax for the LAP were determined to be 84.03 mu M and 357.14 enzymatic units mg(-1), respectively. A noticeable difference of LAP activity between the two insect orders tested was observed. This method could be used to screen for natural LAP inhibitors.