Abstract
Hagfishes are living representatives of the earliest-diverging vertebrates and are thus useful for the study of early vertebrate physiology. It has been previously postulated that digestive enzymes account for the majority of digestion because hagfish are agastric with notable zymogen granules in specialized cells of the hindgut. While the presence of some digestive enzymes (amylase, lipase and leucinaminopeptidase) have been confirmed with histochemistry, quantification of enzymatic activity is limited. This study sought to biochemically quantify the tissue activity of six digestive enzymes (α-amylase, maltase, lipase, trypsin, aminopeptidase and alkaline phosphatase) along the length of the Pacific hagfish (Eptatretus stoutii) alimentary canal. In addition, the effect of feeding on the rate of enzyme activity was examined. Overall, maltase and trypsin activities were unchanging with respect to location or feeding status, while the activities of α-amylase and alkaline phosphatase decreased substantially following feeding, but were consistent along the length. Lipase and aminopeptidase activities were elevated in the anterior region of the alimentary canal in comparison to the more posterior regions, but were not altered with feeding. This study indicates hagfish have an assortment of digestive enzymes that likely are the result of a varied diet. The differential expression of these enzymes along the tract and in regards to feeding may be indications of early compartmentalization of digestive function.
Highlights
Digestion is essential for the catabolism and hydrolysis of ingested macronutrients into smaller molecules suitable for transport
The question yet remains as to whether Pacific hagfish: (1) possess a full complement of digestive enzymes, (2) have differential enzyme distribution along the alimentary canal, and (3) modulate enzyme activity post-feeding. To address these queries we investigated the enzymatic activity for each class of macronutrient. α-amylase and maltase activity were assessed to determine carbohydrate digestion, as polysaccharides such as glycogen are obtained from the liver tissue of prey. α-amylase hydrolyses large polysaccharides into smaller molecules of maltose and glucose, whereas maltase yields glucose from maltose and is an excellent metric to assess complex carbohydrate digestion [12]
Twenty-four Pacific hagfish (Eptatretus stoutii; 65.3 ± 3.5 g; mean ± standard error of the mean (s.e.m)) were collected using traps baited with hake (Merluccius merluccius) in Trevor Channel, Bamfield, B.C., Canada (N48 ̊50.883-W125 ̊08.380) under a license approved by the Department of Fisheries and Oceans Canada
Summary
Digestion is essential for the catabolism and hydrolysis of ingested macronutrients into smaller molecules suitable for transport. It is carried out using mechanical, chemical and enzymatic methods with digestive enzymes released from multiple locations along the alimentary canal. There are a multitude of digestive enzymes for each type of macronutrient, with specifications for substrate and optimal reaction conditions (e.g. acidic vs alkaline), which correspond to their location in the digestive tract and can be derived from the stomach, exocrine pancreas, or the intestinal mucosa itself (reviewed in [1]). The capacity for an organism to digest certain foods predominantly depends upon the presence of appropriate enzymes [2].
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