Metamorphosis of insects in which a larva becomes an adult involves structural changes in most of the tissues and organs to meet the need of an adult insect (SEHNAL
et al., 1996). Insect tissues and organs are classified into following five types, based on the characteristics of the changes at metamorphosis (YAMASHITA, 1986): 1) The tissues such as Malpighian tubules and fat body, that continue to exist but undergo cell remodeling by autophagy of selected cell organelles. 2) The tissues such as a silk gland and some larval muscles, that completely degenerate. 3) The tissue such as a midgut, that continues to exist but larval type cells are degenerated and adult cells are produced from regenerative cells. 4) The tissues such as an epidermis and trachaeol systems, where adult tissues are made from larval tissues. 5) The organs such as gonads, wings, complex eyes and a crop, that newly develop from undifferentiated imaginal discs.
Leucyl-β-naphthylamidase is one kind of an aminopeptidase, which distributes in Malpighian tubules and midgut. It is believed to function in peptide digestion and its absorption. Since its distribution is apparently restricted in the first and third type of tissues, it is likely that the enzyme can be used as a functional marker at the molecular level to study the mechanisms of cell and tissue remodeling at metamorphosis. In the silkworm,
Bombyx mori, some properties of midgut leucyl-β-naphthylamidase were determined (SUMIDA and EGUCHI, 1983a). This midgut enzyme changes its activity in synchronization with metamorphic events of
B. mori (SUMIDA and EGUCHI, 1983b). However, activity of the enzyme of Malpighian tubules are not reported.
In the present paper, therefore, changes in activity of Malpighian tubules leucyl-β-naphthylamidase during development are investigated.
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