Abstract: The activity of phenoloxidase (PO) from the hemolymph and cuticle of Tenebrio molitor larvae was investigated at different time (1-7 h) after molting with the microtitration method. The results showed that the hemolymph PO activity slowly decreased within 3 h after the larva molted but increased at 4-7 h after molting. The cuticle PO activity showed no remarkable changes within 1 h after the larva molted, but decreased at 3 h after molting. The PO activity nearly reached the normal level at 6 h after the larva molted. Meanwhile, determined by LineweaverBurk plot the Km value of PO extracted from the hemolymph and cuticle was 1.176 and 0.881 mmol/L, respectively, indicating that PO from the cuticle has a higher affinity to substrate than that from the hemolymph. The results showed that both cuticle and hemolymph PO were involved in cuticle sclerotization of T. molitor, but have differences in action mode and affinity to substrate.

Key words: Tenebrio molitor, molting, phenoloxidase, cuticle, sclerotization, enzyme activity