Aspartic proteinases in the digestive tract of marine decapod crustaceans.
Decapod crustaceans synthesize highly active proteolytic enzymes in the midgut gland and release at least a part of them into the stomach where they facilitate the first step in peptide hydrolysis. The most common proteinases in the gastric fluid characterized so far are serine proteinases, that is, trypsin and chymotrypsin. These enzymes show highest activities at neutral or slightly alkaline conditions. The presence of acid proteinases, as they prevail in vertebrates, has been discussed contradictorily yet in invertebrates. In this study, we show that acid aspartic proteinases appear in the gastric fluid of several decapods. Lobsters Homarus gammarus showed the highest activity with a maximum at pH 3. These activities were almost entirely inhibited by pepstatin A, which indicates a high share of aspartic proteinases. In other species (Panulirus interruptus, Cancer pagurus, Callinectes arcuatus and Callinectes bellicosus), proteolytic activities were present at acid conditions but were distinctly lower than in H. gammarus. Zymograms at pH 3 showed in each of the studied species at least one, but mostly two-four bands of activity. The apparent molecular weight of the enzymes ranged from 17.8 to 38.6 kDa. Two distinct bands were identified which were inhibited by pepstatin A. Acid aspartic proteinases may play an important role in the process of extracellular digestion in decapod crustaceans. Activities were significantly higher in clawed lobster than in spiny lobster and three species of brachyurans. Therefore, it may be suggested that the expression of acid proteinases is favored in certain groups and reduced in others.
Navarrete del Toro
María de Los Angeles
Mde L
Centro de Investigaciones Biológicas del Noroeste (CIBNOR). P.O. Box 128 La Paz, B.C.S. 23000, México.
García-Carreño
Fernando
F
López
Manuel Díaz
MD
Celis-Guerrero
Laura
L
Saborowski
Reinhard
R
D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000032:analysis* / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D033364:Decapoda / Q000201:enzymology*; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000187:drug effects; D041981:Gastrointestinal Tract / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D007930:Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D010436:Pepstatins / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D014107:Tosyllysine Chloromethyl Ketone / Q000494:pharmacology; D014357:Trypsin / Q000494:pharmacology
D015853:Cysteine Proteinase Inhibitors; D010436:Pepstatins; D011480:Protease Inhibitors; D015842:Serine Proteinase Inhibitors; D014107:Tosyllysine Chloromethyl Ketone; D014357:Trypsin; D016282:Aspartic Acid Endopeptidases; D007930:Leucine; C024974:E 64; C031375:pepstatin