Observations on the feeding mechanism, structure of the gut, and digestive physiology of the european lobster Homarus gammarus (L.) (Decapoda: Nephropidae)

Aspartic Cathepsin D Endopeptidase Contributes to Extracellular Digestion in Clawed Lobsters Homarus americanus and Homarus gammarus

“…Cysteine proteinase activity was already reported in the midgut gland of the American lobster (Laycock et al 1989). The aspartic proteinase cathepsin D1 described in this study and cysteine proteinases seem to contribute to the pool of acid proteinases previously reported by Baker and Gibson (1977), playing an important role in protein digestion in clawed lobsters. The activation mechanism of aspartic proteinases in the gastric fluid of clawed lobsters is still unknown, but given that gastric fluids of lobsters are acid, pH ∼4.7 and also contain cysteine proteinases, it may undergo auto-proteolysis along with assisted activation, similar to pepsinogen and lysosomal procathepsin D of mammals (Tang and Wong 1987).…”

“…After mechanical chopping by the mouth parts, ingested material enters the stomach and mixes with gastric fluid and is hydrolyzed by digestive enzymes derived from the midgut gland (Baker and Gibson 1977). The midgut gland is the site of enzyme synthesis, nutrient absorption, and storage of lipids and glycogen (Glass and Stark 1994;Sánchez-Paz et al 2007).…”

“…The gastric fluid of most decapods has a pH between 5 and 6. The gastric fluid of American and European lobsters, however, is slightly more acidic showing pH 4.7 (Baker and Gibson 1977;Brockerhoff et al 1970; Navarrete del Toro et al 2006;Omondi and Stark 2001).…”

“…In clawed lobsters (Homaridae), digestive proteolytic enzymes have been reported since the early 1970s (Brockerhoff et al 1970;Hoyle 1973), and, unlike other decapods, these proteinases show highest activity at acid pH (Baker and Gibson 1977;Glass and Stark 1994). Cysteine proteinases with optimal activity at acid pH were found in the gastric fluid of American lobster (Laycock et al 1989) and verified by three cathepsin L cDNAs counterparts isolated from the midgut gland (Laycock et al 1991).…”

Changes in midgut gland morphology and digestive enzyme activities associated with development in early stages of the American lobster Homarus americanus

“…Digestion in crustacea is considered to be entirely extracellular (Vonk, 1960;van Wee1, 1970) . Barker and Gibson (1977) claimed to have demonstrated that there is also an intracellular alkaline phase of digestion in H.…”