Serine proteolytic activities in soluble protein
extracted from the larval midgut of Spodoptera littoralis were
studied using specific substrates and protease inhibitors. There are
significant differences in serine activities in respect to larval
development. The serine activities increase with instar development,
reach each maximum at third instar larvae while the lowest serine
activities are observed in the fifth instar larvae. The serine enzymes
are stable at pH ranging from 6-11 with maximum activities at pH
10. Protease inhibitors negatively affect serine activities both in
vitro and in vivo. Ingestion of trypsin inhibitor (SKTI) and
chymotrypsin inhibitor (Chymostatin) cause alteration to larval
development. In general, basic similarities among serine protease
from S. littoralis and other lepidopteran insect digestive proteases in
respect to optimum pH, substrate affinity and response to protease
inhibitor are observed.