title: SERINE proteinase like activity in apolipophorin III from the hemolymph of desert locust, Schistocerca gregaria.
abstract: Apolipophorin III (apoLp-III) has been known as a lipid transport protein of insects. Recent studies indicated the involvement of apoLp-III in immune reactions and in the control of cell destruction, but no enzymatic activity has so far been detected. In the present study, a protease from the hemolymph of Schistocerca gregaria was purified to homogeneity and its enzymatic activity was examined. Identity as chymotrypsin-like proteinase was established by its high affinity toward bulky aromatic substrates and its catalytic specificity for amide or ester bonds on the synthetic substrates, Suc-Ala-Ala-Pro-Xaa-AMC (where Xaa was Phe, Tyr, Trp, and Lys, and AMC is 7-amino-4-methyl-coumarin) and thiolbenzyl ester substrate Suc-Ala-Ala-Pro-Phe-SBzl. The sensitivity for serine protease and chymotrypsin-specific covalent inhibitors, PMSF, TPCK, and noncovalent inhibitors SGCI, showed that it is a chymotrypsin-like proteinase. It showed its maximum activity at pH 8.0 and 55°C for the hydrolysis of Suc-Ala-Ala-Pro-Tyr-AMC. According to similarities in the amino terminal sequence, molar mass (19 kDa) and retention on reversed-phase analytical high-performance liquid chromatography (HPLC) column, this protein is S. gregaria homologue of Locusta migratoria apoLp-III. Our data suggest that apoLp-III also has an inherent proteolytic activity. Results indicated that S. gregaria apoLp-III is a good catalyst and could be used as a biotechnological tool in food processing and in agricultural biotechnology.
authors.affiliation: Department of Medical Pharmacology, University of California, Davis, California 95616, USA. zamalik@ucdavis.edu
authors.forename: Zulfiqar A
authors.initials: ZA
authors.lastname: Malik
authors.forename: Sumaira
authors.initials: S
authors.lastname: Amir
authors.forename: István
authors.initials: I
authors.lastname: Venekei
mesh_terms: D000818:Animals; D001053:Apolipoproteins / Q000302:isolation & purification / Q000378:metabolism*; D006110:Grasshoppers / Q000201:enzymology*; D006458:Hemolymph / Q000201:enzymology*; D019476:Insect Proteins / Q000302:isolation & purification / Q000378:metabolism*; D057057:Serine Proteases / Q000378:metabolism
chemical_list: D001053:Apolipoproteins; D019476:Insect Proteins; C042470:apolipophorin III; D057057:Serine Proteases