Bacterial expression and characterization of starfish phospholipase A(2)

Angiotensin I Converting Enzyme Inhibitory Peptides Derived from Phycobiliproteins of Dulse Palmaria palmata

We examined the inhibitory activity of angiotensin I converting enzyme (ACE) in protein hydrolysates from dulse, Palmaria palmata. The proteins extracted from dulse were mainly composed of phycoerythrin (PE) followed by phycocyanin (PC) and allophycocyanin (APC). The dulse proteins showed slight ACE inhibitory activity, whereas the inhibitory activity was extremely enhanced by thermolysin hydrolysis. The ACE inhibitory activity of hydrolysates was hardly affected by additional pepsin, trypsin and chymotrypsin treatments. Nine ACE inhibitory peptides (YRD, AGGEY, VYRT, VDHY, IKGHY, LKNPG, LDY, LRY, FEQDWAS) were isolated from the hydrolysates by reversed-phase high-performance liquid chromatography (HPLC), and it was demonstrated that the synthetic peptide LRY (IC₅₀: 0.044 μmol) has remarkably high ACE inhibitory activity. Then, we investigated the structural properties of dulse phycobiliproteins to discuss the origin of dulse ACE inhibitory peptides. Each dulse phycobiliprotein possesses α-subunit (Mw: 17,477–17,638) and β-subunit (Mw: 17,455–18,407). The sequences of YRD, AGGEY, VYRT, VDHY, LKNPG and LDY were detected in the primary structure of PE α-subunit, and the LDY also exists in the APC α- and β-subunits. In addition, the LRY sequence was found in the β-subunits of PE, PC and APC. From these results, it was suggested that the dulse ACE inhibitory peptides were derived from phycobiliproteins, especially PE. To make sure the deduction, we carried out additional experiment by using recombinant PE. We expressed the recombinant α- and β-subunits of PE (rPEα and rPEβ, respectively), and then prepared their peptides by thermolysin hydrolysis. As a result, these peptides showed high ACE inhibitory activities (rPEα: 94.4%; rPEβ: 87.0%). Therefore, we concluded that the original proteins of dulse ACE inhibitory peptides were phycobiliproteins.

Effect of feeding on the function and structure of the digestive system in juvenile southern catfish (Silurus meridionalis Chen)

Postprandial physiological and morphological responses to feeding were examined in juvenile southern catfish (Silurus meridionalis Chen) that had consumed a loach (Misgurnus anguillicaudatus Cantor) meal equivalent to 6 % of the body mass of the catfish. The gastric evacuation rate (GER) peaked at 4 h postfeeding, averaging 0.36 g food weight h(-1), at which time 14 % of the ingested meal had passed into the intestine. Less than 10 % of the ingested meal remained in the stomach at 24 h postfeeding. Pepsin activity peaked at 8 h postfeeding, reaching a level approximately twofold higher than the prefeeding level. Pancreatic trypsin activity peaked at 16 h postfeeding, reaching a level 4.5-fold higher than the prefeeding level. Peaks in lipase activity in both the proximal and middle intestinal segments occurred at 16 h, reaching 2.8- and 2.4-fold higher levels than the prefeeding level, respectively, while the activity in the distal intestine segment reached a level 2.9-fold higher than the prefeeding level at 24 h postfeeding. With respect to amylase activity, only the middle intestinal segment exhibited a change, first an increase and then a decrease, after feeding. Feeding also triggered an approximately 200 % increase in the metabolic rate and resulted in 44.6 kJ kg(-1) being expended on specific dynamic action, equivalent to 16.1 % of the meal's energy. In terms of organ size, the wet mass of the liver increased by 11 % at 24 h postfeeding, whereas the wet mass of the pancreas did not change. Except for a decrease in the thickness of the submucosa in the middle intestinal segment, the thickness of the intestinal fold, mucosa, submucosa, muscularis and serosa of each intestinal segment did not change significantly with feeding. These results suggest that the continuum of physiological responses observed with respect to metabolic increases, GER, regulation of pancreatic and intestinal digestive enzyme activities and liver wet mass to feeding corresponds to the changes in the demand on the digestive system in S. meridionalis. Moreover, species maintained stable gastrointestinal tract morphology during the short interval of repeated feeding.

Enzymatic properties of starfish phospholipase A2 and its application

Industrial phospholipase A2 (PLA2) mainly produced from porcine pancreas is used for production of lysolecithin which is well known as an excellent natural emulsifier for food, cosmetic, and pharmaceutical industries. Since the outbreak of bovine spongiform encephalopathy (BSE) or religious tradition, it is hoped that the new sources of PLA2, as well as other enzymes and proteins, will be developed instead of mammal. From these backgrounds, we studied for PLA2 from marine organisms and found that starfish Asterina pectinifera PLA2 possesses extremely high activity and characteristic polar-group specificity comparing with commercially available PLA2 from porcine pancreas. Therefore, it was suggested that the starfish A. pectinifera would be a potential source of PLA2, and the PLA2 can be utilized as alternative enzyme of mammalian PLA2.

Expression and characterization of ARSP1 from Eisenia fetida

To study the characterization of a protease ARSP1 (apoptosis-related serine protease) of Eisenia fetida, a recombinant ARSP1 was constructed. ARSP1 was produced in E. coli BL21-CodonPlus (DE3)-RIL after IPTG induction and exited in inclusion body. After refolding in vitro, the protein was purified by DEAE-Sepharose F.F. and Sephacryl S-100 chromatography in sequence. ARSP1 showed high sequence identity to other chymotrypsin-like serine proteases and the catalytic triad was His41-Asp90-Ser188. ARSP1 could degrade casein following Michaelis-Menten kinetics with a Vmax of 43.9 U/mg protein and a Km for casein of 0.83 g/l. Studies with inhibitors indicated that ARSP1 was a chymotrypsin-like serine protease. Experiments in vitro demonstrated that ARSP1 could not only hydrolyze fibrinogen and fibrin directly, but also activate plasminogen to plasmin. ARSP1 inhibited thrombin activity and ADP-induced platelet aggregation in a dose-response correlation. These results showed that ARSP1 has thrombolytic activity and also an anti-thrombus function.