levis larvae were immobilized on crushed ice and dissected in
cold 342 mMNaCl. The rinsed guts were transferred to a glass slide.
The midgut was isolated and divided into four sections of similar
length (V1, V2, V3, and V4) (Fig. 1). Midgut sections were separated
into tissue and contents and were homogenized in cold doubledistilled
water using a Potter-Elvehjem homogenizer. The homogenates
were centrifuged for 30 min at 20,000 g at 4 8C. The
supernatants were recovered and the pellets (except those of
midgut contents) were resuspended in double-distilled water. The
pellets are regarded as cell membrane fractions. The samples were
stored at 20 8C until use. No enzyme inactivation was detected
during storage.
2.2. pH