ORGANIZATION OF DIGESTION AND PRELIMINARY CHARACTERIZATION OF SALIVARY TRYPSIN-LIKE ENZYMES IN A PREDACEOUS HETEROPTERAN, ZELUS-RENARDII

Salivary and intestinal proteolytic enzymes were studied in the predaceous heteropteran, Zelus renardii. Proteinases from Z. renardii's salivary gland complex (SGC), anterior midgut (AMG) and posterior midgut (PMG) were studied with hemoglobin, BApNA, BTNA, HPLA, HA and LPNA used as substrates. The SGC was shown to be an important source of general proteinase and endopeptidase activity, but exopeptidase activity (LPNA, HPLA and HA hydrolysis) was limited to the AMG and PMG. The AMG was also a source of considerable endopeptidase activity. Hemoglobin or BApNA hydrolysis occurred at a broad range of temperatures and pH with most activity observed at 35-45-degrees-C and at pH 7.0-8.5. The pH of the prey increased, as it was being pre-orally digested. The salivary trypsin-like enzyme had a molecular weight of approx. 27 kDa and eluted as two major activity peaks from an ion exchange column. BApNA hydrolysis was inhibited by soy proteinase inhibitor. Digestion, with respect to protein hydrolysis, is organized into an orderly and highly efficient process, differing greatly from that of hematophagous reduviids, beginning with pre-oral digestion of the prey's internal structures whose liquefaction permits ingestion and further digestive processing of prey within the predator's gut.