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Title: Anopheles stephensi midgut peptidases : characterisation and potential as control targets
Author: Docherty, P. T.
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1998
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This thesis is a study of Anopheles stephensi aminopeptidase and carboxypeptidase activities. The primary objectives of the project were to characterise and identify the peptidase activities, and to determine their roles in mosquito physiology and parasite infectivity. Using biochemical techniques aminopeptidase N was identified in soluble and membrane-associated midgut preparations. Differential centrifugation and enzymatic properties suggested only one aminopeptidase N was present. However, IEF, heat inactivation, and the isolation of two midgut aminopeptidase N gene fragments suggested the presence of two aminopeptidases, a soluble/micellar form and a GPI anchored membrane-associated form. A carboxypeptidase A was also characterised and identified in soluble midgut preparations, and a carboxypeptidase A gene fragment was isolated from midgut tissue. Feeding mosquitoes a specific aminopeptide inhibitor (leuhistin) reduced aminopeptide activity 4.7-fold throughout digestion, suggesting an initial signal was necessary for synthesis of further peptidase. Inhibiting aminopeptides increased the substrate available for carboxypeptidase hydrolysis, thus increasing its activity 2.3-fold when compared with control mosquitoes. In contrast, captopril, a specific carboxypeptidase inhibitor, reduced total carboxypeptidase activity 1.3-fold and increased aminopeptidase activity 1.3-fold. Feeding both inhibitors reduced aminopeptidase activity only. Manipulating peptidase activities did not affect bloodmeal digestion, mosquito mortality or infectivity of Plasmodium berghei to mosquitoes. Fecundity was significantly reduced; mosquitoes laid significantly smaller egg batches than control mosquitoes when fed leuhistin (30%), captopril (70%) and leuhistin + captopril (25%). Ovaries were often malformed, containing one to four developed follicles only. The discussion considers the potential mechanisms for peptidase regulation in mosquitoes, and the possible anti-mosquito and anti-malaria effects of digestive enzymes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available