Developmental changes in midgut leucyl-β-naphthylamidase in the silkworm, Bombyx mori

Abstract

1. 1. l-Leucyl-β-naphthylamidase activity in the midgut was measured during larval-pupal-adult development of the silkworm, Bombyx mori and the properties of larval and pharate adult enzymes were compared after affinity and gel column chromatography. 2. 2. Enzyme activity per individual midgut was high in larval stages reaching a maximum of about 35 μmol/min but dropped at spinning and rose again at the middle of pharate adult development to 3 μmol/min and the activity was maintained until adult emergence. 3. 3. Larval enzymes have been known as membrane-bound, but in pharate adults, two forms of enzyme, membrane-bound (70% of total activity) and soluble form (30%) were present. 4. 4. By gel filtration with Ultrogel AcA 34, solubilized larval enzymes were separated into two main peaks and the solubilized and soluble enzymes from pharate adult were eluted at the positions corresponding to each of the peaks of larval enzymes. 5. 5. Inhibition rate by chemicals and metal ions was similar between enzymes at the same developmental stage compared to those from the larva and pharate adult, suggesting that the enzymes from the two stages are different. 6. 6. Heat stability was different in the enzymes between the larva and pharate adult.