Degradation of leucomyosuppressin by enzymes in the hemolymph and midgut of Lacanobia oleracea and Spodoptera littoralis (Lepidoptera: Noctuidae) larvae

The degradation of 2 nmol synthetic leucomyosuppressin (LMS) by enzymes of the hemolymph, midgut lumen and midgut tissues of both Lacanobia oleracea and Spodoptera littoralis was investigated using reversed-phase high-performance liquid chromatography together with matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). Degradation of LMS in diluted hemolymph of L. oleracea and S. littoralis was not rapid, t1/2 = 65.4 and 13.1 min, respectively, due to carboxypeptidase(s) and endopeptidase(s) present in the hemolymph. There was also some aminopeptidase activity in the hemolymph of both species. However, LMS was rapidly degraded by the diluted contents of the midgut lumen of L. oleracea and S. littoralis, t1/2 = 0.5 and 2.2 min, respectively. The enzymes most likely responsible were trypsin-like serine protease(s) and carboxypeptidase(s). Degradation of LMS by midgut tissues containing 5 μg protein was not rapid in L. oleracea or S. littoralis, t1/2 = 40.7 and 69.8 min, respectively. The most abundant degradation products probably resulted from carboxypeptidase activity, but some aminopeptidase activity was also detected.