Isolation and characterization of a trypsin fraction from the pyloric ceca of chinook salmon (Oncorhynchus tshawytscha)

Trypsin from Pyloric Caeca of Asian Seabass: Purification, Characterization, and Its Use in the Hydrolysis of Acid-Soluble Collagen

The study aimed to purify trypsin from the pyloric caeca of Asian seabass (Lates calcarifer), and investigate its proteolytic capability toward acid-soluble collagen (ASC) in comparison with commercial porcine trypsin (CPT). Trypsin was purified from pyloric caeca, a leftover from the evisceration process, via ammonium sulphate (40-60% saturation) precipitation, and a soybean trypsin inhibitor (SBTI)-Sepharose 4B column. A 18.5-fold purification and a yield of 15.2% were obtained. SDS-PAGE analysis confirmed a single band of trypsin with a molecular weight of 23.5 kDa. Purified trypsin also showed the single band in native-PAGE. The optimal pH and temperature of trypsin for BAPNA (the specific substrate for amidase) hydrolysis were 8.5 and 60 °C, respectively. The trypsin was stable within the pH range of 7.0-9.5 and temperature range of 25-55 °C. Protease inhibition study confirmed that the purified enzyme was trypsin. The purified trypsin had a Michaelis-Menten constant (Km) and catalytic constant (kcat) of 0.078 mM and 5.4 s-1, respectively, when BAPNA was used. For the hydrolysis of TAME (the specific substrate for esterase), the Km and Kcat were 0.09 mM and 4.8 s-1, respectively. Partially purified seabass trypsin (PPST) had a slightly lower hydrolysis capacity toward ASC than CPT, as evidenced by the lower degree of hydrolysis and protein degradation when the former was used. Both the α-chain and β-chain became more degraded as the hydrolysis time increased. Based on MALDI-TOP, peptides with MW of 2992-2970 Da were dominant in the hydrolysates. Therefore, seabass trypsin could be used in the production of hydrolyzed collagen. It could have economic importance to the market, by replacing some commercial proteases, which have religious constraints.

Physicochemical and Biochemical Properties of Trypsin-like Enzyme from Two Sturgeon Species

This work aimed to determine the physicochemical and biochemical properties of trypsin from beluga Huso huso and sevruga Acipenser stellatus, two highly valuable sturgeon species. According to the results obtained from the methods of casein-zymogram and inhibitory activity staining, the molecular weight of trypsin for sevruga and beluga was 27.5 and 29.5 kDa, respectively. Optimum pH and temperature values for both trypsins were recorded at 8.5 and 55 °C by BAPNA (a specific substrate), respectively. The stability of both trypsins was well-preserved at pH values from 6.0 to 11.0 and temperatures up to 50 °C. TLCK and SBTI, two specific trypsin inhibitors, showed a significant inhibitory effect on the enzymatic activity of both trypsins (p < 0.05). The enzyme activity was significantly increased in the presence of Ca⁺² and surfactants and decreased by oxidizing agents, Cu⁺², Zn⁺², and Co⁺² (p < 0.05). However, univalent ions Na⁺ and K⁺ did not show any significant effect on the activity of both trypsins (p > 0.05). The results of our study show that the properties of trypsin from beluga and sevruga are in agreement with data reported in bony fish and can contribute to the clear understanding of trypsin activity in these primitive species.

Fishery Wastes as a Yet Undiscovered Treasure from the Sea: Biomolecules Sources, Extraction Methods and Valorization

The search for new biological sources of commercial value is a major goal for the sustainable management of natural resources. The huge amount of fishery by-catch or processing by-products continuously produced needs to be managed to avoid environmental problems and keep resource sustainability. Fishery by-products can represent an interesting source of high added value bioactive compounds, such as proteins, carbohydrates, collagen, polyunsaturated fatty acids, chitin, polyphenolic constituents, carotenoids, vitamins, alkaloids, tocopherols, tocotrienols, toxins; nevertheless, their biotechnological potential is still largely underutilized. Depending on their structural and functional characteristics, marine-derived biomolecules can find several applications in food industry, agriculture, biotechnological (chemical, industrial or environmental) fields. Fish internal organs are a rich and underexplored source of bioactive compounds; the fish gut microbiota biosynthesizes essential or short-chain fatty acids, vitamins, minerals or enzymes and is also a source of probiotic candidates, in turn producing bioactive compounds with antibiotic and biosurfactant/bioemulsifier activities. Chemical, enzymatic and/or microbial processing of fishery by-catch or processing by-products allows the production of different valuable bioactive compounds; to date, however, the lack of cost-effective extraction strategies so far has prevented their exploitation on a large scale. Standardization and optimization of extraction procedures are urgently required, as processing conditions can affect the qualitative and quantitative properties of these biomolecules. Valorization routes for such raw materials can provide a great additional value for companies involved in the field of bioprospecting. The present review aims at collecting current knowledge on fishery by-catch or by-products, exploring the valorization of their active biomolecules, in application of the circular economy paradigm applied to the fishery field. It will address specific issues from a biorefinery perspective: (i) fish tissues and organs as potential sources of metabolites, antibiotics and probiotics; (ii) screening for bioactive compounds; (iii) extraction processes and innovative technologies for purification and chemical characterization; (iv) energy production technologies for the exhausted biomass. We provide a general perspective on the techno-economic feasibility and the environmental footprint of the production process, as well as on the definition of legal constraints for the new products production and commercial use.

Interplays between copper and Mycobacterium tuberculosis GroEL1

The chaperone GroEL1 enhances copper tolerance during Mycobacterium bovis BCG biofilm formation. The binding of copper ions to the GroEL1 histidine-rich region protects the chaperone from destabilization and increases its ATPase activity.

Fish trypsins: potential applications in biomedicine and prospects for production

In fishes, trypsins are adapted to different environmental conditions, and the biochemical and kinetic properties of a broad variety of native isoforms have been studied. Proteolytic enzymes remain in high demand in the detergent, food, and feed industries; however, our analysis of the literature showed that, in the last decade, some fish trypsins have been studied for the synthesis of industrial peptides and for specific biomedical uses as antipathogenic agents against viruses and bacteria, which have been recently patented. In addition, innovative strategies of trypsin administration have been studied to ensure that trypsins retain their properties until they exert their action. Biomedical uses require the production of high-quality enzymes. In this context, the production of recombinant trypsins is an alternative. For this purpose, E. coli-based systems have been tested for the production of fish trypsins; however, P. pastoris-based systems also seem to show great potential in the production of fish trypsins with higher production quality. On the other hand, there is a lack of information regarding the specific structures, biochemical and kinetic properties, and characteristics of trypsins produced using heterologous systems. This review describes the potential uses of fish trypsins in biomedicine and the enzymatic and structural properties of native and recombinant fish trypsins obtained to date, outlining some prospects for their study.

Two trypsin isoforms from albacore tuna (Thunnus alalunga) liver: Purification and physicochemical and biochemical characterization

Two trypsins (A and B) from the liver of albacore tuna (Thunnus alalunga) were purified to homogeneity using a series of column chromatographies including Sephacryl S-200, Sephadex G-50 and Diethylaminoethyl-cellulose. Purity was increased to 80.35- and 101.23-fold with approximately 3.1 and 19.2% yield for trypsins A and B, respectively. The molecular weights of trypsins A and B were estimated to be 21 and 24kDa, respectively, by SDS-PAGE and size exclusion chromatography. Both trypsins showed only one band on native-PAGE. Trypsins A and B exhibited the maximal activity at 60°C and 55°C, respectively, and had the same optimal pH at 8.5 using N^α-p-Tosyl-l-arginine methyl ester hydrochloride (TAME) as a substrate. Stabilities of both trypsins were well maintained at a temperature up to 50°C and in the pH range of 7.0-11.0 and were highly dependent on the presence of calcium ion. The inhibition test demonstrated strong inhibition by soybean trypsin inhibitor and TLCK. Activity of both trypsins continuously decreased with increasing NaCl concentration (0-30%). The N-terminal amino acid sequence of 20 residues of the two trypsin isoforms had homology when compared to those of other fish trypsins.

Purification and characterization of trypsin from Luphiosilurus alexandri pyloric cecum

Trypsin from L. alexandri was purified using only two purification processes: ammonium sulfate precipitation and anion exchange liquid chromatography in DEAE-Sepharose. Trypsin mass was estimated as 24 kDa through SDS-PAGE, which showed only one band in silver staining. The purified enzyme showed an optimum temperature and pH of 50 °C and 9.0, respectively. Stability was well maintained, with high levels of activity at a pH of up to 11.0, including high stability at a temperature of up to 50 °C after 60 min of incubation. The inhibition test demonstrated strong inhibition by PMSF, a serine protease inhibitor, and Kinetic constants km and kcat for BAPNA were 0.517 mM and 5.0 S-1, respectively. The purified enzyme was also as active as casein, as analyzed by zymography. Therefore, we consider trypsin a promising enzyme for industrial processes, owing to its stability in a wide range of pH and temperature and activity even under immobilization.

Influence of time, storage temperature and freeze/thaw cycles on the activity of digestive enzymes from gilthead sea bream (Sparus aurata)

In this study, we tested the effects of long-term storage (2 years) at -20 °C and short-term storage (several hours) in ice and freeze/thaw cycles on the activities of pancreatic, gastric and intestinal (brush border and cytosolic) digestive enzymes in a teleost fish species. The results revealed a significant lose in activity of pancreatic (trypsin, chymotrypsin, total alkaline proteases and α-amylase) and intestinal cytosolic (leucine-alanine peptidase) enzymes between 140 and 270 days of storage at -20 °C, whereas in contrast, the activity of all the assayed brush border enzymes remained constant during the first 2 years of storage at -20 °C. During short-term storage conditions, the most stable enzymes assayed were those of the enterocytes of the brush border, which did not show any change in activity after being held for 5 h in ice. Five freezing and thawing cycles did not affect the activity of the intestinal brush border enzymes and the cytosolic ones, whereas the activity of trypsin, α-amylase and bile-salt-activated lipase was significantly affected by the number of freezing and thawing cycles. No changes in pepsin activity were found in samples exposed to 1 and 2 freezing and thawing cycles.

Purification and characterization of trypsin from the pyloric ceca of orange-spotted grouper, Epinephelus coioides

Trypsin from the pyloric ceca of orange-spotted grouper, Epinephelus coioides, was purified by fractionation with ammonium sulfate, ionic exchange, and affinity chromatography. The protein was purified 161.85-fold with a yield of 4%. Purified trypsin had an apparent molecular weight of 24 kDa according to an SDS-PAGE analysis. Optimal profiles of temperature and pH of the enzyme were 50°C and 8-10, respectively, using Nα-benzoyl-L: -arginine ethyl ester as the substrate. The results of thermal and pH stability assays showed that the enzyme was stable at temperatures of up to 50°C and in the pH range of 6-8. Trypsin activity decreased with an increasing NaCl concentration (0-0.6 M). The activity of purified trypsin was effectively inhibited by a soybean trypsin inhibitor and N-p-tosyl-L: -lysine chloromethyl ketone, and was slightly inhibited by iodoacetic acid, ethylenediaminetetraacetic acid, 1-(L: -trans-epoxysuccinyl-leucylamino)-4-guanidinobutane, and pepstatin A. Protein identification of the purified protease showed that the sequences of two peptides, LGEHNI and NLDNDIML, were highly homologous to other fish trypsins. The measurement of trypsin activity in different tissues showed that the highest activity was detected in pyloric ceca, followed by anterior intestine, middle intestine, hind intestine and spleen, but very low activities were found in other tissues. An inverse relationship between the trypsin activity in four tissues of pyloric ceca, anterior intestine, middle intestine and hind intestine and fish body weight as a result of increased pepsin in stomach indicated grouper growth status was increased.

Characterisation of trypsin purified from the viscera of Tunisian barbel (Barbus callensis) and its application for recovery of carotenoproteins from shrimp wastes

Trypsin was purified from the viscera of barbel by precipitation using ammonium sulphate (0-80%), Sephadex G-100, and Mono Q-Sepharose ion exchange chromatography. The trypsin was purified 27-fold, with 79U/mg specific activity and 31% recovery. The enzyme had a molecular weight of 24kDa; purified trypsin appeared as a single band on native-PAGE. The optimum pH and temperature for enzyme activity were pH 10.0 and 55°C with BAPNA used as a substrate. The N-terminal amino acid sequence of the first 12 amino acids of the purified trypsin was IVGGYECTPYSQ. The Michaelis-Menten constant (K_m) and catalytic constant (k_cat) values of the enzyme were 0.018mM and 1.21s^-1, respectively. The study also investigated the effects of purified trypsin on the recovery of carotenoproteins from shrimp (Parapenaeus longirostris) shells through hydrolysis using 1.0U barbel trypsin/g shrimp shells for 1h at 30°C. The freeze-dried carotenoproteins recovered contained 71.09% protein, 16.47% lipid, 7.78% ash, and 1.79% chitin.

Trypsin from the viscera of Bogue (Boops boops): isolation and characterisation

Trypsin from the viscera of Bogue (Boops boops) was purified to homogeneity by precipitation with ammonium sulphate, Sephadex G-100 gel filtration and Mono Q-Sepharose anion exchange chromatography, with an 8.5-fold increase in specific activity and 36% recovery. The molecular weight of the purified enzyme was estimated to be 23 kDa by SDS-PAGE and size exclusion chromatography. The purified trypsin appeared as a single band on native-PAGE and zymography staining. The purified enzyme showed esterase-specific activity on N-α-benzoyl-L-arginine ethyl ester (BAEE) and amidase activity on N-α-benzoyl-DL-arginine-p-nitroanilide (BAPNA). The optimum pH and temperature for the enzyme activity, after 10 min incubation, were pH 9.0 and 55°C, respectively, using BAPNA as a substrate. The trypsin kinetic constants Km and kcat on BAPNA were 0.13 mM and 1.56 s(-1), respectively, while the catalytic efficiency kcat/Km was 12 s(-1) mM(-1). Biochemical characterisation of B. boops trypsin showed that this enzyme can be used as a possible biotechnological tool in the fish processing and food industries.

Purification and properties of digestive lipases from Chinook salmon (Oncorhynchus tshawytscha) and New Zealand hoki (Macruronus novaezelandiae)

Lipases were purified from delipidated pyloric ceca powder of two New Zealand-sourced fish, Chinook salmon (Oncorhynchus tshawytscha) and hoki (Macruronus novaezelandiae), by fractional precipitation with polyethylene glycol 1000, followed by affinity chromatography using cholate-Affi-Gel 102, and gel filtration on Sephacryl S-300 HR. For the first time, in-polyacrylamide gel activity of purified fish lipases against 4-methylumbelliferyl butyrate has been demonstrated. Calcium ions and sodium cholate were absolutely necessary both for lipase stability in the gel and for optimum activity against caprate and palmitate esters of p-nitrophenol. A single protein band was present in native polyacrylamide gels for both salmon and hoki final enzyme preparations. Under denaturing conditions, electrophoretic analysis revealed two bands of 79.6 and 54.9 kDa for salmon lipase. It is proposed that these bands correspond to an uncleaved and a final form of the enzyme. One band of 44.6 kDa was seen for hoki lipase. pI values of 5.8±0.1 and 5.7±0.1 were obtained for the two salmon lipase forms. The hoki lipase had a pI of 5.8±0.1. Both lipases had the highest activity at 35°C, were thermally labile, had a pH optimum of 8-8.5, and were more acid stable compared to other fish lipases studied to date. Both enzymes were inhibited by the organophosphate paraoxon. Chinook salmon and hoki lipases showed good stability in several water-immiscible solvents. The enzymes had very similar amino acid composition to mammalian carboxyl ester lipases and one other fish digestive lipase. The salmon enzyme was an overall better catalyst based on its higher turnover number (3.7±0.3 vs. 0.71±0.05 s(-1) for the hoki enzyme) and lower activation energy (2.0±0.4 vs. 7.6±0.8 kcal/mol for the hoki enzyme) for the hydrolysis of p-nitrophenyl caprate. The salmon and hoki enzymes are homologous with mammalian carboxyl ester lipases.

Biochemical properties of anionic trypsin acting at high concentration of NaCl purified from the intestine of a carnivorous fish: smooth hound (Mustelus mustelus)

Trypsin from the intestine of smooth hound (Mustelus mustelus) was purified by fractionation with ammonium sulfate, Sephadex G-75 gel filtration, and DEAE-cellulose ion exchange chromatography, with a 65-fold increase in specific activity and 15% recovery. The molecular weight of the purified trypsin was estimated to be 24 kDa using size exclusion chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The purified enzyme showed esterase-specific activity on N(alpha)-p-tosyl-L-arginine methyl ester hydrochloride (TAME) that was four times greater than its amidase-specific activity on Nalpha-benzoyl-DL-arginine-p-nitroanilide (BAPNA). The optimum pH and temperature for the trypsin activity were pH 8.5 and 50 degrees C, respectively, using TAME as a substrate. The enzyme was extremely stable in the pH range of 7.0-9.0 and highly stable up to 40 degrees C after 1 h of incubation. The purified enzyme was strongly inhibited by soybean trypsin inhibitor (SBTI) and N-p-tosyl-1-lysine chloromethyl ketone (TLCK), specific inhibitors for trypsin. In addition, smooth hound trypsin showed higher proteolytic activity at high NaCl concentration, demonstrating its potential for protein hydrolysis at high salt content. The N-terminal amino acid sequence of the first 12 amino acids of the purified trypsin was IVGGYECKPHSQ. This sequence showed high homology with trypsins from marine vertebrates and invertebrates. Purified trypsin had a Michaelis-Menten constant (K(m)) and catalytic constant (K(cat)) of 0.387 +/- 0.02 mM and 2.62 +/- 0.11 s(-1), respectively, when BAPNA was used as a substrate. For the hydrolysis of TAME, K(m) and K(cat) were 0.156 +/- 0.01 mM and 59.15 +/- 2.2 s(-1), respectively.

Purification, characterization and substrate specificity of a trypsin from the Amazonian fish tambaqui (Colossoma macropomum)

An enzyme was purified from the pyloric caecum of tambaqui (Colossoma macropomum) through heat treatment, ammonium sulfate fractionation, Sephadex G-75 and p-aminobenzamidine-agarose affinity chromatography. The enzyme had a molecular mass of 23.9 kDa, NH(2)-terminal amino acid sequence of IVGGYECKAHSQPHVSLNI and substrate specificity for arginine at P1, efficiently hydrolizing substrates with leucine and lysine at P2 and serine and arginine at P1'. Using the substrate z-FR-MCA, the enzyme exhibited greatest activity at pH 9.0 and 50 degrees C, whereas, with BAPNA activity was higher in a pH range of 7.5-11.5 and at 70 degrees C. Moreover, the enzyme maintained ca. 60% of its activity after incubated for 3h at 60 degrees C. The enzymatic activity significantly decreased in the presence of TLCK, benzamidine (trypsin inhibitors) and PMSF (serine protease inhibitor). This source of trypsin may be an attractive alternative for the detergent and food industry.

Purification and characterization of trypsin from the intestine of hybrid tilapia (Oreochromis niloticusxO.aureus)

Trypsin from the intestine of hybrid tilapia (Oreochromis niloticus x O.aureus) was purified by the following techniques: acetone precipitation, ammonium sulfate fractionation, Sephacryl S-200 gel filtration, and DEAE-sephacel ion exchange chromatography. The purified enzyme was determined to be homogeneous by polyacrylamide gel electrophoresis (PAGE) and sodium dodecyl sulfate (SDS)-PAGE. The molecular weight was estimated as 22,000 Da. The optimum pH and temperature of the enzyme for the hydrolysis of casein were determined to be 9.0 and 60 degrees C, respectively. The enzyme was stable over a broad pH range from 7.0 to 12.0 at 30 degrees C, and the enzyme was inactive at temperatures above 50 degrees C. The behavior of the enzyme for the hydrolysis of casein followed Michaelis-Menten kinetics with Km of 0.46 mg/mL. The purified enzyme was inhibited by the general serine protease inhibitor phenyl methyl sulphonyl fluoride (PMSF) and also by the specific trypsin inhibitor N-p-tosyl-L-lysine chloromethyl ketone (TLCK) using Nalpha-CBZ-L-lysine p-nitrophenyl ester hydrochloride (CBZ-Lys.pNP) as a substrate. The protease was inhibited by the following ions in decreasing order: Zn2+>Fe3+>Cu2+>Al3+>Co2+=Pb2+>Cd2+>Mn2+. The ions Li+, Na+, K+, Mg2+, and Ba2+ had little effect on the enzyme, and Ca2+ can partially promote its activity at low concentration.

A laundry detergent-stable alkaline trypsin from striped seabream (Lithognathus mormyrus) viscera: purification and characterization

An alkaline trypsin from the intestine of striped seabream (Lithognathus mormyrus) was purified and characterized. The enzyme was purified to homogeneity by precipitation with ammonium sulfate, Sephadex G-100 gel filtration and CM-Sephadex cation-exchange chromatography, with a 24.9-fold increase in specific activity and 13% recovery. The molecular weight of the purified alkaline trypsin was estimated to be 27.5 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and size exclusion chromatography. The purified trypsin appeared as a single band on native PAGE. Interestingly, the enzyme was highly active over a wide range of pH from 8.0 to 11.0, with an optimum at pH 10.0 using Nalpha-benzoyl-dl-arginine-p-nitroanilide (BAPNA) as a substrate. The relative activities at pH 8.0, 11.0, and 12.0 were 73%, 67% and 50.4%, respectively. The enzyme was extremely stable over a broad pH range (5.0-12.0). The optimum temperature for enzyme activity was 50 degrees C. The purified enzyme was strongly inhibited by soybean trypsin inhibitor (SBTI). In addition, the enzyme showed excellent stability toward various surfactants and bleache agents and compatibility with some commercial solid and liquid detergents. The trypsin kinetic constants, Km and kcat of the enzyme for BAPNA, were 0.29 mM and 1.36 s(-1), respectively, while the catalytic efficiency kcat/Km was 4.68 s(-1) mM(-1).

Comparative study on the proteases from fish pyloric caeca and the use for production of gelatin hydrolysate with antioxidative activity

Proteases from pyloric caeca extract of three fish species including brownstripe red snapper (Lutjanus vitta), bigeye snapper (Priacanthus tayenus) and threadfin bream (Nemipterus marginatus) were comparatively studied. The extracts from bigeye snapper and threadfin bream exhibited the highest hydrolytic activities toward casein, alpha-N-benzoyl-DL-arginine-p-nitroanilide and alpha-N-rho-tosyl-L-arginine methyl ester at pH 8.0 and 60 degrees C and pH 8.5 and 55 degrees C, respectively. The extract of brownstripe red snapper showed the optimal pH and temperature of 8.0 and 60 degrees C with all substrates used except the optimal temperature was 65 degrees C when casein was used. All proteases were strongly inhibited by soybean trypsin inhibitor (SBTI) and N-rho-tosyl-L-lysine chloromethylketone (TLCK) and partially inhibited by N-tosyl-L-phenylalanine chloromethylketone for all substrates tested, suggesting that trypsin-like proteases were the major enzymes. Substrate-gel activity staining of 40-60% ammonium sulfate (AS) fraction revealed that major activity bands were observed with molecular mass of 24, 22 and 20 kDa for brownstripe red snapper, bigeye snapper and threadfin bream, respectively. Those activity bands were partially inhibited by SBTI and TLCK. AS fraction was further used to produce gelatin hydrolysate from the skin of brownstripe red snapper with different degrees of hydrolysis (DH). Hydrolysate with DH of 15% exhibited the highest DPPH and ABTS radical scavenging activities and ferric reducing antioxidant power (p<0.05). Therefore, the extract from pyloric caeca could be used to produce the gelatin hydrolysates possessing antioxidative activities.

Trypsin from the pyloric caeca of bluefish (Pomatomus saltatrix)

Trypsin was purified from the pyloric caeca of bluefish (Pomatomus saltatrix) by ammonium sulfate precipitation, acetone precipitation and soybean trypsin inhibitor-Sepharose 4B affinity chromatography. Bluefish trypsin migrated as a single band using both sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and native-PAGE and had a molecular mass of 28 kDa. The optima pH and temperature for the hydrolysis of benzoyl-dl-arginine-p-nitroanilide (BAPNA) were 9.5 and 55 degrees C, respectively. The enzyme was stable over a broad pH range (7 to 12), but was unstable at acidic pH, and at temperatures greater than 40 degrees C. The enzyme was inhibited by specific trypsin inhibitors: soybean trypsin inhibitor (SBTI), N-p-tosyl-l-lysine chloromethyl ketone (TLCK) and the serine protease inhibitor phenylmethyl sulfonylfluoride (PMSF). CaCl2 partially protected trypsin against activity loss at 40 degrees C, but NaCl (0 to 30%) decreased the activity in a concentration dependent manner. The N-terminal amino acid sequence of trypsin was determined as IVGGYECKPKSAPVQVSLNL and was highly homologous to other known vertebrate trypsins.