Characterization of the peptidases of Calliphora: Many features allow the utilization of small peptides as an amino acid reservoir |
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| Institution: | 1. Research Group on Bioactive Substances, Federal University of Agreste from Pernambuco, Garanhuns, Brazil;2. Laboratory of Biotechnology, Federal University of Agreste from Pernambuco, Garanhuns, Brazil;3. Institute of Chemistry and Biotechnology, Federal University of Alagoas, Maceió, Brazil;1. School of Life Science and Bioengineering, Nelson Mandela African Institution of Science and Technology, PO Box 447, Arusha, Tanzania;2. Department of Chemistry, University of Dar es Salaam, Mkwawa University College of Education, PO Box 2513, Iringa, Tanzania;1. College of Light Industry, Textile & Food Engineering, Sichuan University, Chengdu 610065, China;2. Key Laboratory for Leather Chemistry and Engineering of the Education Ministry, Sichuan University, Chengdu 610065, China;3. National Engineering Research Centre of Solid-State Brewing, Luzhou 646000, China |
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| Abstract: | Electrophoretic separation of whole flies and of haemolymph indicates the presence of four peptidases, named dipeptidase A, B and C (Dip A, B and C) and leucine amino peptidase (LAP) after enzymes of similar substrate specificities and electrophoretic mobilities found in Drosophila (Laurie-Ahlberg, Biochem. Genet.20, 407–424, 1982; Walker et al., Insect Biochem.10, 535–541, 1980). Prominent in both tissues and haemolymph, dipeptidase A and B together hydrolyse a variety of dipeptides in vitro and probably most of the fly's small peptide component in vivo. Though Dip A and Dip B hydrolyse many of the same substrates, their activities differ in at least several respects. Dip A's Kms are higher than Dip B's Kms and hence in vivo the two enzymes together are likely to provide peptide hydrolysis through a wide range of substrate concentration. Dip A's unique hydrolyses are of peptides with biosynthesized amino acids in the N-terminal position and Dip B's unique hydrolyses are of peptides with essential amino acids in the N-terminal position. Dip B, but not Dip A, is inhibited by free amino acid. It is inhibited non-competitively and most strongly by essential amino acids. In cell-free haemolymph Dip B's activity is more stable than Dip A's. The accumulation and maintenance of small peptides in times of dietary sufficiency and the utilization of the small peptides as a source of amino acid in times of dietary scarcity (Collett, Insect Biochem.6, 179–185, 1976a; J. Insect Physiol.22, 1433–1440, 1976b) may be attributed to these features. |
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