Cysteine and serine proteolytic activities in larval midgut of yellow mealworm, Tenebrio molitor L. (Coleoptera: Tenebrionidae)
Thie, NMR.; Houseman, JG.
Insect Biochemistry 20(7): 741-744
The midgut of the yellow mealworm, Tenebrio molitor, contains both serine and cysteine proteolytic activities, identified using synthetic substrates, pH optima characteristic for each enzyme, diagnostic activators and inhibitors. The cysteine proteinase, detected by optimal hydrolysis of N-benzoyl-dl-arginine-ß-naphthylamide at pH 5.0, was activated by thiol compounds, inhibited by the cysteine specific proteinase inhibitors iodoacetamide (IAA) and trans-epoxysuccinyl-l-leucyl-amido(4guanidino)-butane (E-64). The serine proteinase detected by maximal hydrolysis of benzoyl-dl-arginine-p-nitroanilide at pH 8.0, was inhibited by the serine specific proteinase inhibitors aprotinin, soybean trypsin inhibitor, PMSF and activity was not affected by either IAA or E-64. Both proteinase activities were higher in gut contents compared to wall and higher cysteine proteolytic activity occurred in the anterior, compared to posterior, portion of the midgut. Serine proteolytic activity predominated in the posterior region of the midgut.