Digestive processes of haematophagous insects. XI. Partial purification and some properties of six proteolytic enzymes from the tsetse fly Glossina morsitans morsitans Westwood (Diptera: Glossinidae)

Abstract

By O-(diethylaminoethyl)cellulose (DEAE-cellulose) chromatography, affinity chromatography, and Sephadex gel filtration, six proteolytic enzymes active in alkaline medium have been found in the digestive portion of the midgut (tissue and lumen contents) of adult Glossina morsitans morsitans. By use of synthetic substrates the enzymes have been characterized as aminopeptidase (AP; EC. 3.4.11.1), carboxypeptidase A (CPA; EC 3.4.12.2), carboxypeptidase B (CPB; EC 3.4.12.3), trypsin (EC 3.4.21.4), a trypsinlike enzyme designated proteinase VI, and a chymotrypsinlike enzyme designated proteinase VII. By Sephadex G-100 gel filtration the molecular weights were estimated to be 20 000 for trypsin, 19 000 for proteinase VI, 35 500 for proteinase VII, 30 000 for CPA, 22 000 for CPB, and [Formula: see text] for AP. The Km values (mg/ml) for haemoglobin were 3.43 for trypsin, 2.45 for proteinase VI, 3.68 for proteinase VII, and 2.42 for CPA. The Km values for casein were 1.22 for trypsin and 1.38 for proteinase VII. Casein showed substrate inhibition when hydrolyzed by proteinase VI and VII. Neither haemoglobin nor casein was hydrolyzed by AP and CPB. The pH optima were determined for hydrolysis of casein and the synthetic substrates.