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Title: Inhibition of digestive enzyme release by neuropeptides in larvae of Opisina arenosella (Lepidoptera: Cryptophasidae)

item Nachman, Ronald

Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2002
Publication Date: 3/22/2002
Citation: Harshini, S., Nachman, R.J., Sreekumar, S. 2002. Inhibition of digestive enzyme release by neuropeptides in larvae of Opisina arenosella (Lepidoptera: Cryptophasidae). Comparative Biochemistry and Physiology. 132:353-358.

Interpretive Summary: Because of problems with the development of resistance to conventional pesticides, there is a critical need for new concepts and alternative approaches in controlling insect pests. The basic premise of this research is that neuropeptides (short chains of amino acids) serve as potent internal messengers in insects to regulate vital functions. New, selective control measures may be developed by designing metabolically stable mimics of these neuropeptides that actively inhibit or over-stimulate functions regulated by them, resulting in disruption of the internal environment of the insect. We report on work that demonstrates that neuropeptides of the "leucokinin" and "LPK" classes inhibit release of digestive enzymes that metabolize proteins and carbohydrates. A deeper understanding of how these neuropeptides regulate aspects of the process of digestion will aid in the design of strategies to disrupt feeding and survival. The work brings us one step closer to the development of practical neuropeptide-like substances that will be effective in controlling pest insects in an environmentally friendly fashion.

Technical Abstract: Leucokinins are a group of structurally related neuropeptides stimulating gut motility and fluid secretion by Malpighian tubules in insects. For studying the effect of neuropeptides on digestive enzyme release, empty midgut tubes of larvae of Opisina arenosella ligated at both ends with hair were incubated with leucokinins (LK I-VIII), LK analogues and leucopyrokinin (LPK) in a bioassay apparatus at 37 C for 30 minutes. The lumen contents were subsequently analyzed for digestive enzyme levels. The neuropeptides LK III, FFSWGamide, 122A, LPK and 434 inhibited the release of digestive enzymes protease and amylase while LK VIII, unique in having a tyrosine residue, stimulated protease enzyme release. The minimum sequence of amino acids at the C-terminal required for activity of LK peptides was found to be FXSWGamide (X = Asn, His, Ser, or Trp). The N-terminal pyroglutamate residue and proline at the C-terminal may contribute to the inhibitory effect of LPK on digestive enzyme release. The present study reveals for the first time an inhibitory effect for the leucokinins and pyrokinins on the release of digestive enzymes from the insect midgut.