Similar Amino Acid Compositions Research Articles

Physical-Chemical Properties of Collagens from Skin, Scale, and Bone of Grass Carp (Ctenopharyngodon idellus)

In order to study the similarities and differences of physical-chemical properties of collagens from different parts of the fish body, acid-soluble collagens and pepsin-soluble collagens were isolated from skin, scale, and bone of grass carp (Ctenopharyngodon idellus), with yields ranging from 0.7 to 25.5% on the basis of dry weight. The content of acid-soluble collagen in skin and scale was much higher than that in bone according to the data of extraction yield. Collagens from grass carp have similar amino acid composition, protein patterns, and sequences of primary structure. Thermal transition temperatures of collagens from different parts of grass carp body decreased in the order of bone > skin > scale. The pepsin-soluble collagens showed more resistance to collagenase, compared to acid-soluble collagens extracted from the same part of the grass carp body. All grass carp collagens did not induce a significant cytotoxic effect according to the results of in vitro cytotoxicity test.

Signal peptide discrimination and cleavage site identification using SVM and NN

About 15% of all proteins in a genome contain a signal peptide (SP) sequence, at the N-terminus, that targets the protein to intracellular secretory pathways. Once the protein is targeted correctly in the cell, the SP is cleaved, releasing the mature protein. Accurate prediction of the presence of these short amino-acid SP chains is crucial for modelling the topology of membrane proteins, since SP sequences can be confused with transmembrane domains due to similar composition of hydrophobic amino acids. This paper presents a cascaded Support Vector Machine (SVM)-Neural Network (NN) classification methodology for SP discrimination and cleavage site identification.The proposed method utilises a dual phase classification approach using SVM as a primary classifier to discriminate SP sequences from Non-SP. The methodology further employs NNs to predict the most suitable cleavage site candidates. In phase one, a SVM classification utilises hydrophobic propensities as a primary feature vector extraction using symmetric sliding window amino-acid sequence analysis for discrimination of SP and Non-SP. In phase two, a NN classification uses asymmetric sliding window sequence analysis for prediction of cleavage site identification.The proposed SVM-NN method was tested using Uni-Prot non-redundant datasets of eukaryotic and prokaryotic proteins with SP and Non-SP N-termini. Computer simulation results demonstrate an overall accuracy of 0.90 for SP and Non-SP discrimination based on Matthews Correlation Coefficient (MCC) tests using SVM. For SP cleavage site prediction, the overall accuracy is 91.5% based on cross-validation tests using the novel SVM-NN model.

Construction of proteins with molecular recognition capabilities using 3 3 de novo protein scaffolds

The molecular recognition ability of proteins is essential in biological systems, and therefore a considerable amount of effort has been devoted to constructing desired target-binding proteins using a variety of naturally occurring proteins as scaffolds. However, since generating a binding site in a native protein can often affect its structural properties, highly stable de novo protein scaffolds may be more amenable than the native proteins. We previously reported the generation of de novo proteins comprising three α-helices and three β-strands (α3β3) from a genetic library coding simplified amino acid sets. Two α3β3 de novo proteins, vTAJ13 and vTAJ36, fold into a native-like stable and molten globule-like structures, respectively, even though the proteins have similar amino acid compositions. Here, we attempted to create binding sites for the vTAJ13 and vTAJ36 proteins to prove the utility of de novo designed artificial proteins as a molecular recognition tool. Randomization of six amino acids at two linker sites of vTAJ13 and vTAJ36 followed by biopanning generated binding proteins that recognize the target molecules, fluorescein and green fluorescent protein, with affinities of 10(-7)-10(-8) M. Of note, the selected proteins from the vTAJ13-based library tended to recognize the target molecules with high specificity, probably due to the native-like stable structure of vTAJ13. Our studies provide an example of the potential of de novo protein scaffolds, which are composed of a simplified amino acid set, to recognize a variety of target compounds.

Down-regulation of OsSAG12-1 results in enhanced senescence and pathogen-induced cell death in transgenic rice plants

Senescence is a highly regulated process accompanied by changes in gene expression. While the mRNA levels of most genes decline, the mRNA levels of specific genes (senescence associated genes, SAGs) increase during senescence. Arabidopsis SAG12 (AtSAG12) gene codes for papain-like cysteine protease. The promoter of AtSAG12 is SA-responsive and reported to be useful to delay senescence by expressing cytokinin biosynthesis gene isopentenyltransferase specifically during senescence in several plants including Arabidopsis, lettuce and rice. The physiological role of AtSAG12 is not known; the homozygous atsag12 mutant neither fails to develop senescenceassociated vacuoles nor shows any morphological phenotype. Through BLAST search using AtSAG12 amino acid sequences as query, we identified a few putative homologues from rice genome (OsSAGs; Oryza sativa SAGs). OsSAG12-1 is the closest homologue of AtSAG12 with 64% similar amino acid composition. Expression of OsSAG12-1 is induced during senescence and pathogen-induced cell death. To evaluate the possible role of OsSAG12-1 we generated RNAi transgenic lines in Japonica rice cultivar TP309. The transgenic lines developed early senescence at varying levels and showed enhanced cell death when inoculated with bacterial pathogen Xanthomonas oryzae pv.oryzae. Our results suggest that OsSAG12-1 is a negative regulator of cell death in rice.

Effect of pH and ethanol content of solvent on rheology of zein solutions

Zein, a corn protein, is a mixture of the polypeptides α-, γ-, β-, and δ-zein. α-Zein and γ-zein comprise 70–85% and 10–20% of total zein mass, respectively. Both peptides have similar amino acid composition, except γ-zein is rich in cysteine. The presence of cysteine has been associated with gelation of zein solutions. A common solvent for zein is aqueous ethanol. Preliminary results suggested that pH and ethanol content affect the rheology of zein solutions. Our objective was to investigate the effect of ethanol content (65–90%) and pH of the solvent (2, 6, and 12) on rheological properties of zein solutions (20% w/w) containing γ-zein. Steady shear tests and oscillatory time sweeps were performed to determine flow behavior and gelation time of zein solutions. Results indicated that α-zein solutions were nearly Newtonian while those containing γ-zein showed shear thinning behavior. At high pH, γ-zein increased the consistency index (K) and shortened gelation time. Results were attributed to the cysteine in γ-zein. High pH promoted formation of disulfide bonds leading to higher K values and shorter gelation times. Results of this work are expected to be useful in the design of zein extraction processes and the development of new zein applications.

Timing of isotopic integration in marine mammal skull: comparative study between calcified tissues

Tissues with different turnover rates have different isotope compositions and reflect the different periods in an animal's life when the isotopes are incorporated during the growth of tissues. Bone is one of the most used tissues for reconstruction of an animal's diet; however, the time of isotope integration remains unknown for many species. The δ(15)N and δ(13)C values in tooth dentine and bone tissue from the maxilla and mandible of 21 stranded northern elephant seals, Mirounga angustirostris, collected on the San Benito and Magdalena Islands, Mexico, between 2000 and 2008 were compared. Bone and dentine samples from each growth layer within the tooth were analyzed using a PDZ Europa ANCA-GSL elemental analyzer interfaced with a PDZ Europa 20-20 continuous flow gas source mass spectrometer. The δ(15)N and δ(13)C values were not different between bone structures, indicating similar turnover rates, metabolic activity and amino acid compositions. The differences in the observed δ(13)C values between tissues are probably indicative of differences in their amino acid compositions, although the similarities in δ(15)N values indicated less variation from different amino acids. Correlation of the analyses between isotopic values of tissues suggests that the maxilla and/or mandible of M. angustirostris might reflect the δ(15) N signal incorporated during the last 5 years of life of the individuals. This study demonstrated the usefulness of the applied approach for providing a best approximation of the timing of isotopic integration into the skull of a marine mammal, thereby reducing uncertainty in exploring historic changes in the species' feeding behavior.

Assessing the Coupling in cis between Disordered Regions and Ordered Domains

A majority of intrinsically disordered regions occur in cis with ordered domains. This suggests the possibility of functional synergy between ordered domains and disordered regions. Such coupling between distinct modules opens the possibility for increased versatility in protein functions through combinatorial diversity. Despite this, the coupling between ordered domains and disordered regions has been largely unexplored. Here, we build on our growing understanding of the intrinsic conformational preferences of disordered regions to assess the degree and nature of the modulation of these preferences by cis-acting ordered domains. We use SH3/SH2 domains of NcK adapter proteins and disordered linkers attached to these domains as archetypes of ordered domains in cis with disordered regions. We use atomistic simulations to quantify the intrinsic conformational preferences of different linker sequences. In doing so, we establish that sequence permutants of linkers with similar amino acid compositions can have considerably different conformational preferences. We next use a combination of atomistic and coarse grain simulations to interrogate the nature and degree of coupling between disordered regions and ordered domains. In particular, we quantify and compare the extent of conformational coupling between ordered SH2/SH3 domains for different linker sequences of fixed amino acid compositions and linker sequences with different compositions. We show how insights from the resultant conformational phase diagram are relevant for explaining the phase behavior of copolymers of ordered domains connected by linkers and for heterotypic interactions in signaling pathways that are mediated through synergy between SH2/SH3 domains and their disordered linkers.

Disease mutations in the prion-like domains of hnRNPA1 and hnRNPA2/B1 introduce potent steric zippers that drive excess RNP granule assembly.

Approximately 1% of human proteins harbor a prion-like domain (PrLD) of similar low complexity sequence and amino acid composition to domains that drive prionogenesis of yeast proteins like Sup35. PrLDs are over-represented in human RNA-binding proteins and mediate phase transitions underpinning RNP granule assembly. This modality renders PrLDs prone to misfold into conformers that accrue in pathological inclusions that characterize various fatal neurodegenerative diseases. For example, TDP-43 and FUS form cytoplasmic inclusions in amyotrophic lateral sclerosis (ALS) and mutations in TDP-43 and FUS can cause ALS. Here, we review our recent discovery of discrete missense mutations that alter a conserved gatekeeper aspartate residue in the PrLDs of hnRNPA2/B1 and hnRNPA1 and cause multisystem proteinopathy and ALS. The missense mutations generate potent steric zippers in the PrLDs, which enhance a natural propensity to form self-templating fibrils, promote recruitment to stress granules and drive cytoplasmic inclusion formation. PrLDs occur in ~250 human proteins and could contribute directly to the etiology of various degenerative disorders.

Physico-chemical characterization and biological evaluation of two fibroin materials

Silk fibroin fibres from two different sources, Bombyx mori pure-breed silkworms and polyhybrid cross-bred silkworm cocoons, were treated with formic acid under planar stirring conditions to prepare non-woven nets. The treatment partially dissolved the fibres, which bound together and formed a non-woven micrometric net with fibres coated by a thin layer of low molecular weight fibroin matrix. The starting fibres, net materials and fibroin coating layer were characterized in terms of amino acid composition, molecular weight and calorimetric properties. In vitro cell culture tests with rat fibroblasts were performed to investigate cell proliferation, morphology and spreading. Moreover, host-rat fibroblasts were preseeded on the afore-mentioned nets and implanted in the thorax of rats for histological analysis. In spite of the chemical differences between the two starting fibroins, the response of the said materials in vitro and in vivo were very similar. These results suggest that the outcome is likely correlated with the modification of the processing technique; that during the formation of the net, a thin gel layer of similar amino acid composition was formed on the fibroin fibres.

Bioinformatic study of the relationship between protein regulation and sequence properties

Although protein expression and regulation have been intensively studied, a complete picture of its mechanisms is still to be drawn. Analysis of high-throughput quantitative proteomics data provides a way to better understand protein regulation. Here, we introduce a bioinformatic analysis method to correlate protein regulation with individual amino acid patterns. We compare the amino acid composition between groups of regulated and unregulated proteins and investigate the correlation between codon usage patterns and protein regulation levels in two Sulfolobus species in “biofilm vs planktonic” experiments. The identified amino acids can then be associated with the regulation of specific gene functions. Strikingly, our analysis shows that functional categories of regulated proteins with similar composition and codon usage pattern of specific amino acids behave similarly. This finding can contribute to a better understanding of protein and gene expression regulation and could find applications in gene optimisation.

Buried organic horizons represent amino acid reservoirs in boreal forest soils

We examined the composition and concentration of amino acids by soil horizon and depth on the Tanana River floodplain in interior Alaska. Soils from mid-successional stages of balsam poplar and white spruce were separated into successive forest floor (Oe/Oa), buried organic horizons (BOHs), and mineral horizons; and water-extractable amino acid composition and concentration were determined by HPLC. The number, depth, and thickness of BOHs were highly variable across the landscape and among replicates of the same stand type, reflecting differences in terrace age, flood frequency, flood intensity, river channel position, vegetation inputs, and decomposition. BOHs generally had lower pH and bulk density, higher moisture content, and greater concentrations of carbon, nitrogen, and roots than the surrounding mineral horizons. In each horizon of both successional stages, the soil amino acid pool was dominated by glutamic acid, glutamine, alanine, asparagine, aspartic acid, and histidine, which together accounted for approximately 80% of the total amino acids found. Despite the similar overall amino acid composition among the horizons, proportions of glutamine generally increased with depth and were generally greater in the mineral horizons than in the BOHs, suggesting root exudation or fine root turnover as an amino acid source. In both successional stages, amino acid concentrations were nearly always highest in the Oe/Oa horizon and rapidly decreased with depth. BOHs generally had greater amino acid concentrations than the surrounding mineral horizons in both successional stages, but amino acid concentrations in successive BOHs declined with depth in the soil profile, suggesting that although BOHs do remain as biological hot spots and potential nutrient reservoirs as far down as 60 cm depth, their importance declines over time.

Interaction of the Profilaggrin N-Terminal Domain with Loricrin in Human Cultured Keratinocytes and Epidermis

The relationship between the two coexpressed differentiation markers, profilaggrin and loricrin, is not clear right now. In this study, we explored the interaction of profilaggrin N-terminal domain (PND) with loricrin in keratinocytes and epidermis. Confocal immunofluorescence microscopic analysis of human epidermis showed that PND colocalized with loricrin. Loricrin nucleofected into HaCaT cells colocalized with PND in the nucleus and cytoplasm. The PND localizes to both the nucleus and cytoplasm of epidermal granular layer cells. Nucleofected PND also colocalized with keratin 10 (K10) in the nucleus and cytoplasm. Immunoelectron microscopic analysis of human epidermis confirmed the findings in nucleofected keratinocytes. Yeast two-hybrid assays showed that the B domain of human and mouse PND interacted with loricrin. The glutathione S-transferase (GST) pull-down analysis using recombinant GST-PND revealed that PND interacted with loricrin and K10. Knockdown of PND in an organotypic skin culture model caused loss of filaggrin expression and a reduction in both the size and number of keratohyalin granules, as well as markedly reduced expression of loricrin. Considering that expression of PND is closely linked to keratinocyte terminal differentiation, we conclude that PND interacts with loricrin and K10 in vivo and that these interactions are likely to be relevant for cornified envelope assembly and subsequent epidermal barrier formation.

Heterogeneous distributions of amino acids provide evidence of multiple sources within the Almahata Sitta parent body, asteroid 2008 TC3

Abstract– Two new fragments of the Almahata Sitta meteorite and a sample of sand from the related strewn field in the Nubian Desert, Sudan, were analyzed for two to six carbon aliphatic primary amino acids by ultrahigh performance liquid chromatography with UV‐fluorescence detection and time‐of‐flight mass spectrometry (LC‐FT/ToF‐MS). The distribution of amino acids in fragment #25, an H5 ordinary chondrite, and fragment #27, a polymict ureilite, were compared with results from the previously analyzed fragment #4, also a polymict ureilite. All three meteorite fragments contain 180–270 parts‐per‐billion (ppb) of amino acids, roughly 1000‐fold lower than the total amino acid abundance of the Murchison carbonaceous chondrite. All of the Almahata Sitta fragments analyzed have amino acid distributions that differ from the Nubian Desert sand, which primarily contains l‐α‐amino acids. In addition, the meteorites contain several amino acids that were not detected in the sand, indicating that many of the amino acids are extraterrestrial in origin. Despite their petrological differences, meteorite fragments #25 and #27 contain similar amino acid compositions; however, the distribution of amino acids in fragment #27 was distinct from those in fragment #4, even though both are polymict ureilites from the same parent body. Unlike in CM2 and CR2/3 meteorites, there are low relative abundances of α‐amino acids in the Almahata Sitta meteorite fragments, which suggest that Strecker‐type chemistry was not a significant amino acid formation mechanism. Given the high temperatures that asteroid 2008 TC3 appears to have experienced and lack of evidence for aqueous alteration on the asteroid, it is possible that the extraterrestrial amino acids detected in Almahata Sitta were formed by Fischer‐Tropsch/Haber‐Bosch type gas‐grain reactions at elevated temperatures.

Voltage-gated sodium channel-associated proteins and alternative mechanisms of inactivation and block.

Voltage-gated sodium channels mediate inward current of action potentials upon membrane depolarization of excitable cells. The initial transient sodium current is restricted to milliseconds through three distinct channel-inactivating and blocking mechanisms. All pore-forming alpha subunits of sodium channels possess structural elements mediating fast inactivation upon depolarization and recovery within milliseconds upon membrane repolarization. Accessory subunits modulate fast inactivation dynamics, but these proteins can also limit current by contributing distinct inactivation and blocking particles. A-type isoforms of fibroblast growth factor homologous factors (FHFs) bear a particle that induces long-term channel inactivation, while sodium channel subunit Navβ4 employs a blocking particle that rapidly dissociates upon membrane repolarization to generate resurgent current. Despite their different physiological functions, the FHF and Navβ4 particles have similarity in amino acid composition and mechanisms for docking within sodium channels. The three competing channel-inactivating and blocking processes functionally interact to regulate a neuron's intrinsic excitability.

Isolation and characterization of three cold acclimation-responsive dehydrin genes from Eucalyptus globulus

The molecular and physiological work related to cold hardiness in Eucalyptus globulus and the cold-responsive dehydrins is reported. The identification and full-length gene sequence of three dehydrins of 10, 20, and 30 kDa and the comparison of their promoters regarding to potential stress and hormone response elements in E. globulus are shown. The categorization of cold-responsive proteins as dehydrin was based on the similarity in amino acid composition with selected sequenced peptides from chilling-responsive dehydrin reported for other woody plants and the increasing of gene expression level during cold acclimation. The transcript accumulation for these three dehydrin genes increased with cold acclimation and decreased with deacclimation in leaf and stem tissues, being higher in a freezing-resistant genotype of E. globulus compared to a sensitive genotype. By western blot, five dehydrin peptides were identified which increased their expression, under cold stress in leaf and stem tissues. These results provide valuable information about cold acclimation and gene regulation in eucalypt genotypes that differ in their ability to tolerate frost temperature.

Extraction, Purification and Characterization of Fish Chymotrypsin: A Review

Problem statement: Solid fish waste is generated from the unwanted parts of fish including heads, tails, fins, frames, offal (guts, kidney and liver) and skin. It accounts for up to 80% of material from production of surimi, 66% from production of fillet and 27% from production of headed and gutted fish. Currently, fish wastes are disposed off in land-based waste disposal systems or at sea generating toxic by-products during the decomposition process. However, fish processing waste can be used to produce commercially valuable by-products, such as chymotrypsin. Approach: A comperehensive review of the literature on the extraction, purification and characeterization of fish chymotrypsin was performed. Results: Chymotrypsin is an endopeptidase secreted by the pancreatic tissues of vertebrates and invertebrates. It has 3 different structures (chymotrypsin A, B and C) varying slightly in solubility, electrophoretic mobility, isoelectric point and cleavage specificity. Only chymotrypsin A and B are found in fish. Compared with mammal chymotrypsin, fish chymotrypsins have similar amino acid composition and molecular weights. Fish chymotrypsins have higher specific activity, especially those from cold-water fish, and low pH and temperature tolerance. The factors affecting the concentration and activity of chymotrypsin in fish are water temperature, fish species, fish age, fish weight and starvation. Chymotrypsin has application in various industries including the food industry, leather production industry chemical industry and medical industry. Conclusion: Extraction techniques for chymotrypsin include: ultra-filtration, ammonium sulphate fractionation precipitation or water-in-oil microemulsions. Purification can be carried out using re-crystallization and gel-filtration, ion-exchange and hydrophobic interaction chromatography. Further studies should focus on the optimization of purifiying chymotrypsin from fish processing wastes.

Structure-Function Analysis of Diacylglycerol Acyltransferase Sequences from 70 Organisms

BackgroundDiacylglycerol acyltransferase families (DGATs) catalyze the final and rate-limiting step of triacylglycerol (TAG) biosynthesis in eukaryotic organisms. Understanding the roles of DGATs will help to create transgenic plants with value-added properties and provide clues for therapeutic intervention for obesity and related diseases. The objective of this analysis was to identify conserved sequence motifs and amino acid residues for better understanding of the structure-function relationship of these important enzymes.Results117 DGAT sequences from 70 organisms including plants, animals, fungi and human are obtained from database search using tung tree DGATs. Phylogenetic analysis separates these proteins into DGAT1 and DGAT2 subfamilies. These DGATs are integral membrane proteins with more than 40% of the total amino acid residues being hydrophobic. They have similar properties and amino acid composition except that DGAT1s are approximately 20 kDa larger than DGAT2s. DGAT1s and DGAT2s have 41 and 16 completely conserved amino acid residues, respectively, although only two of them are shared by all DGATs. These residues are distributed in 7 and 6 sequence blocks for DGAT1s and DGAT2s, respectively, and located at the carboxyl termini, suggesting the location of the catalytic domains. These conserved sequence blocks do not contain the putative neutral lipid-binding domain, mitochondrial targeting signal, or ER retrieval motif. The importance of conserved residues has been demonstrated by site-directed and natural mutants.ConclusionsThis study has identified conserved sequence motifs and amino acid residues in all 117 DGATs and the two subfamilies. None of the completely conserved residues in DGAT1s and DGAT2s is present in recently reported isoforms in the multiple sequences alignment, raising an important question how proteins with completely different amino acid sequences could perform the same biochemical reaction. The sequence analysis should facilitate studying the structure-function relationship of DGATs with the ultimate goal to identify critical amino acid residues for engineering superb enzymes in metabolic engineering and selecting enzyme inhibitors in therapeutic application for obesity and related diseases.

Methods to collect, preserve, and prepare elasmobranch tissues for stable isotope analysis

Stable isotope analysis has the potential to expand our understanding of elasmobranch ecology. However, elasmobranchs share unique traits (i.e., retention of urea, lack of adipose tissue, cartilaginous skeletons) that require modified preparation techniques. Alternative tissue collection and preservation methods would allow sampling from ichthyology collections and at remote locations. We compared different collection, preservation, and preparation techniques to identify treatments that yielded robust isotopic data. Blood components collected in tubes coated with lithium heparin (an anti-coagulant) were not isotopically distinct from blood collected in no-additive tubes. Compared to frozen muscle, ethanol-treated muscle had altered δ13C values, but similar δ15N values. Finally, we removed lipids and urea with petroleum ether and deionized water, respectively. Although untreated and treated muscle had similar amino acid compositions, treated muscle preferentially lost 14N and had greater C:N ratios. These results indicate that urea affects isotope ratios and that water treatment removes urea without altering muscle protein composition. Although not exhaustive, our study begins to address the need for elasmobranch-specific methods.

Structure and properties of cocoons and silk fibers produced by Hyalophora cecropia

This paper shows that silk fibers produced by cecropia (Hyalophora cecropia) have similar tensile properties but different amino acid composition than that of mulberry (Bombyx mori) silk. The cecropia fibers are also much finer and have bet ter strength and modulus than tasar silk, the most common non-mulberry silk. Cecropia is one of the largest silk producing moths and has similar lifecycle to that of mulberry silk but is easier to grow and produces larger cocoons than mulberry silk. In this study, we have characterized the composition, morphology, physical and tensile properties, and thermal behavior of the cecropia silk. Cecropia cocoons have a three tier structure and are larger (750 mg) than the cocoons produced by B. mori (650 mg). Fibers in the three layers in cecropia cocoons have tensile properties similar to that of B. mori silk but are finer (1.7–2 denier) and have higher strength (3.8–4.3 g/denier) and modulus (68–92 g/denier) than tasar silk.

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.