Inhibition kinetics of green crab (Scylla serrata) alkaline phosphatase activity by dithiothreitol or 2-mercaptoethanol

Zymography assisted quick purification, characterization and inhibition analysis of K. pneumoniae alkaline phosphatase by mercury and thiohydroxyal compounds

In-gel hydrolysis of para-nitrophenyl phosphate (p-NPP) to yellow colored para-nitrophenol was used to locate precisely the K. pneumoniae alkaline phosphatase (Kp-ALKP) on 7% native PAGE. Subsequent removal of the yellow-stained band and electroelution yielded a 54 kDa, Kp-ALKP with K_m, V_max and k_cat values of (0.7 ± 0.02) mM, (80 ± 4.5) μmol min^-1 and (39.2 ± 2.2) × 10⁴ s^-1 respectively for p-NPP. Kp-ALKP was optimally active at 70 °C and pH 7.2 that was activated by Mg²⁺, Ca²⁺, Co²⁺ and inhibited by EDTA, PO₄, Pb²⁺, Cu²⁺ and Hg²⁺. The enzyme was trypsin resistant and retained 75% activity in presence of 10 mM PO₄ and 65% activity at 3 mM Hg²⁺ showing it's PO₄^3- irrepressibility and Hg²⁺-tolerance. Molecular dynamics simulation revealed increased structural stability of Kp-ALKP at 70 °C that accounts for it's optimal temperature. Zymography revealed that both DTT and β-mercaptoethanol induced activity loss accompanied by mobility retardation of Kp-ALKP on 7% native PAGE. These results and in Silico analysis shows that both DTT and βME reduce the C³⁰⁸-C³⁵⁸ disulfide bond, leading to an open conformation of the enzyme. However, Hg²⁺ had negligible effect on the in-gel mobility of Kp-ALKP indicating it's plausible non-covalent interaction with surface-accessible amino-acids without significant conformational change. For the first time our study reveals the zymography as an easy, inexpensive and convenient tool for quick purification, characterization and conformational analysis of K. pneumoniae alkaline phosphatase.

Comparison of biochemical composition of commercial sea cucumbers, Apostichopus japonicus and Parastichopus californicus, under the same culture conditions

BACKGROUND

Apostichopus japonicus and Parastichopus californicus are two of the most important and profitable commercial sea cucumbers along the North Pacific coast. This study compared the body wall production rate (BWPR), proximate composition, amino acid, fatty acid, trace element and vitamin composition, and nonspecific immune enzyme activities of A. japonicus and P. californicus cultured in an artificial pond.

RESULTS

The BWPR, crude fat and ash content in the body walls of A. japonicus and P. californicus showed remarkable differences (P < 0.05). For the 18 amino acids tested, differences in the contents of 15 were significant (P < 0.05) between the two species, except for threonine, methionine and histidine, and their first limiting amino acids were both methionine+cysteine. There were seven saturated and ten unsaturated fatty acids in their body walls, and except for 18:1 and 20:1, the content differences of the other 15 fatty acids were all significant (P < 0.05). Furthermore, between the two sea cucumbers, differences in the content of seven trace elements (Cu, Fe, Mn, Zn, Cr, Ni, Se) and six vitamins (B1, B3, B5, B9, C, E) were significant (P < 0.05). The activities of superoxide dismutase (SOD), catalase (CAT), acid phosphatase (ACP) and alkaline phosphatase (AKP) also showed distinct differences (P < 0.05).

CONCLUSION

There are greater differences in the biochemical compositions and contents between A. japonicus and P. californicus, each with its own unique quality advantages. A. japonicus and P. californicus have high nutritional value, which are both the superior sea cucumbers. © 2022 Society of Chemical Industry.

Effects of Ocean Acidification on Molting, Oxidative Stress, and Gut Microbiota in Juvenile Horseshoe Crab Tachypleus tridentatus

Anthropogenic elevation of atmospheric carbon dioxide (CO2) drives global-scale ocean acidification (OA), which has aroused widespread concern for marine ecosystem health. The tri-spine horseshoe crab (HSC) Tachypleus tridentatus has been facing the threat of population depletion for decades, and the effects of OA on the physiology and microbiology of its early life stage are unclear. In this study, the 1st instar HSC larvae were exposed to acidified seawater (pH 7.3, pH 8.1 as control) for 28 days to determine the effects of OA on their growth, molting, oxidative stress, and gut microbiota. Results showed that there were no significant differences in growth index and molting rate between OA group and control group, but the chitinase activity, β-NAGase activity, and ecdysone content in OA group were significantly lower than those of the control group. Compared to the control group, reactive oxygen species (ROS) and malondialdehyde (MDA) contents in OA group were significantly increased at the end of the experiment. Superoxide dismutase (SOD), catalase (CAT), and alkaline phosphatase (AKP) activities increased first and then decreased, glutathione peroxidase (GPX) decreased first and then increased, and GST activity changed little during the experiment. According to the result of 16S rRNA sequencing of gut microbiota, microbial-mediated functions predicted by PICRUSt showed that "Hematopoietic cell lineage," "Endocytosis," "Staphylococcus aureus infection," and "Shigellosis" pathways significantly increased in OA group. The above results indicate that OA had no significant effect on growth index and molting rate but interfered with the activity of chitinolytic enzymes and ecdysone expression of juvenile horseshoe crabs, and caused oxidative stress. In addition, OA had adverse effects on the immune defense function and intestinal health. The present study reveals the potential threat of OA to T. tridentatus population and lays a foundation for the further study of the physiological adaptation mechanism of juvenile horseshoe crabs to environmental change.

Construction and analysis of the immune effect of Vibrio harveyi subunit vaccine and DNA vaccine encoding TssJ antigen

Vibrio harveyi, a severe pathogen infects different kinds of sea animals, causes huge economic loss in aquaculture industry. In order to control the Vibriosis disease caused mainly by V. harveyi and other Vibrio spp., the best solution lies in developing corresponding efficient vaccines. In this study, we have cloned and analysed a putative antigen TssJ from the T6SS of V. harveyi, which has the potential as a vaccine against infection. The sequence analysis and western blotting experiments indicated that TssJ anchored in outer membrane and there were several antigenic determinants existed on its extracellular region. Two forms of universal vaccines, subunit vaccine and DNA vaccine, were developed based on TssJ and applied in Trachinotus ovatus. The results showed that both of the two vaccines could generate a moderate protection in fish against V. harveyi. The relative percentage survival (RPS) of subunit vaccine and DNA vaccine were 52.39% and 69.11%, respectively. Immunological analysis showed both subunit vaccine and DNA vaccine enhanced acid phosphatase, alkaline phosphatase, superoxide dismutase, and lysozyme activities. Specific serum antibodies against TssJ in the fish vaccinated with subunit vaccine was much higher than that in the DNA vaccine group. Several immune-related genes, i.e., IL10, C3, MHC Iα, MHC IIα, and IgM, were induced both by the two forms of vaccines. TNFα and Mx were only upregulated in the DNA vaccine group. However, the induction levels of these genes induced by DNA vaccine were higher than subunit vaccine. All these findings suggested that TssJ from V. harveyi had a potential application value in vaccine industry.

Effects of Lycium barbarum polysaccharides on immunological parameters, apoptosis, and growth performance of Nile tilapia (Oreochromis niloticus)

In this study, the effect of Lycium barbarum polysaccharides (LBP) on immunological parameters, apoptosis, and growth performance of Nile tilapia (Oreochromis niloticus) was investigated. Dietary supplementation with LBP significantly increased complement 3 (C3) activity and promoted interleukin IL-1β gene expression in spleen tissue, significantly reduced apoptosis in spleen tissue, increased the specific growth rate (SGR), relative length gain (LG), and relative weight gain (WG) of Nile tilapia. However, dietary supplementation with LBP did not have a significant effect on serum alkaline phosphatase (AKP), malondialdehyde (MDA), and superoxide dismutase (SOD), blood constituents, apoptosis, or gene expression of IL-1β in liver tissue. Overall, the results showed that dietary supplementation with LBP increased the nonspecific immunity of Nile tilapia and reduced the apoptosis rate to promote growth and development. Thus, LBP has potential for use as a new immunostimulant in aquaculture.

Soil mineral alters the effect of Cd on the alkaline phosphatase activity

The toxicity of heavy metals (HMs) to soil enzymes is directly influenced by the status of the enzyme (free vs. immobilized on minerals) and the duration of exposure. However, little information is available on the interaction effect of HMs, mineral, and exposure time on soil enzyme activities. We investigated the interaction mechanism of alkaline phosphatase (ALP) with minerals (montmorillonite and goethite) and the response of free and immobilized ALP to cadmium (Cd) toxicity under different exposure times. The adsorption isotherms of ALP on both minerals were L-type. The maximum adsorption capacity of goethite for ALP was 3.96 times than montmorillonite, although both had similar adsorption constant (K). Goethite showed a greater inhibitory effect on ALP activity than montmorillonite. The toxicity of Cd to free- and goethite-ALP was enhanced with increasing exposure time, indicating a time-dependent inhibition. However, Cd toxicity to montmorillonite-ALP was not affected by the exposure time. The inhibition of Cd to soil enzyme activity is influenced by the properties of mineral complexes and the duration of exposure. A further understanding of the time pattern of HMs toxicity is helpful for accurately assessing the hazards of HMs to soil enzyme activity.

Effects of a probiotic (Bacillus licheniformis) on the growth, immunity, and disease resistance of Haliotis discus hannai Ino

To study the effects of a probiotic (Bacillus lincheniformis) on the survival and growth of Haliotis discus hannai Ino, the expression levels of nonspecific immune genes and the resistance to Vibrio parahaemolyticus infection were assessed. Abalones (shell length: 27.64 ± 1.59 mm, body weight: 4.17 ± 0.32 g) were selected for use in an 8-week culture experiment and a 2-week V. parahaemolyticus artificial infection experiment. In both experiments, the control group (C) was fed with a basal feed and the experimental groups were fed with experimental food prepared by spraying the probiotic on the basal feed at different concentrations: 10³ (B1), 10⁵ (B2), and 10⁷ (B3) cfu/mL. The survival rate, total number of blood lymphocytes, activity of acid phosphatase, and expression level of heat shock protein 70 were significantly higher in B1, B2, and B3 than in C (P < 0.05). The specific growth rate of shell length, food intake, food conversion rate, phagocytic activity of blood lymphocytes, activities of myeloperoxidase and catalase (CAT), and expression levels of CAT and thioredoxin peroxidase of abalones in B2 were significantly higher than those in B1 and C (P < 0.05). Although the level of O₂^- produced by the respiratory burst of blood lymphocytes in B2 was not significantly different from those in B1 and B3, they were significantly higher than that in C (P < 0.05). The activity of superoxide dismutase (SOD), the nitric oxide levels produced by the respiratory burst of blood lymphocytes, and the expression levels of Mn-SOD in B1 and B3 were significantly higher than those in C but significantly lower than those in B2 (P < 0.05). Fourteen days after infection with V. parahaemolyticus, the cumulative mortality of abalones in B2 was significantly lower than those in B1 and C (P < 0.05). These results indicate that the food containing 10⁵ cfu/mL Bacillus licheniformis promoted food intake and growth of abalones and also improved their resistance to V. parahaemolyticus infection. Thus, B. licheniformis is a good potential probiotic.

Kinetics and mechanism of jack bean urease inhibition by Hg2+

BACKGROUND

Jack bean urease (EC 3.5.1.5) is a metalloenzyme, which catalyzes the hydrolysis of urea to produce ammonia and carbon dioxide. The heavy metal ions are common inhibitors to control the rate of the enzymatic urea hydrolysis, which take the Hg2+ as the representative. Hg2+ affects the enzyme activity causing loss of the biological function of the enzyme, which threatens the survival of many microorganism and plants. However, inhibitory kinetics of urease by the low concentration Hg2+ has not been explored fully. In this study, the inhibitory effect of the low concentration Hg2+ on jack bean urease was investigated in order to elucidate the mechanism of Hg2+ inhibition.

RESULTS

According to the kinetic parameters for the enzyme obtained from Lineweaver-Burk plot, it is shown that the Km is equal to 4.6±0.3 mM and Vm is equal to 29.8±1.7 μmol NH3/min mg. The results show that the inhibition of jack bean urease by Hg2+ at low concentration is a reversible reaction. Equilibrium constants have been determined for Hg2+ binding with the enzyme or the enzyme-substrate complexes (Ki =0.012 μM). The results show that the Hg2+ is a noncompetitive inhibitor. In addition, the kinetics of enzyme inhibition by the low concentration Hg2+ has been studied using the kinetic method of the substrate reaction. The results suggest that the enzyme first reversibly and quickly binds Hg2+ and then undergoes a slow reversible course to inactivation. Furthermore, the rate constant of the forward reactions (k+0) is much larger than the rate constant of the reverse reactions (k-0). By combining with the fact that the enzyme activity is almost completely lost at high concentration, the enzyme is completely inactivated when the Hg2+ concentration is high enough.

CONCLUSIONS

These results suggest that Hg2+ has great impacts on the urease activity and the established inhibition kinetics model is suitable.

Modification and modificatory kinetics of the active center of prawn beta-N-acetyl-D-glucosaminidase

Beta-N-acetyl-D-glucosaminidase (NAGase, EC3.2.1.52) plays important role in molting, digestion of chitinous foods, and defense systems against parasites in prawn (Litopenaeus vannamei). However, study on functional groups and catalytic mechanism of NAGase are yet limited. The modification of the active center of NAGase from prawn has been first studied. The results demonstrate that the disulfide bonds and the carbamidine groups of arginine residues are not essential to the enzyme's activity. The modification of indole group of tryptophan of the enzyme by N-bromosuccinimide (NBS) can lead to the complete inactivation, accompanying the absorption decreasing at 276 nm, indicating that tryptophan is essential residue to the enzyme. The modificatory kinetics of NAGase in the appropriate concentrations of NBS solution has been studied and the numbers of essential tryptophan residues have been determined using the kinetic method of the substrate reaction. The result shows that only one tryptophan residue is essential for enzyme activity. And the modifications of histidine, lysine residue, and the carboxyl groups also inactivate the enzyme completely or incompletely. The results showed that the carboxyl groups of acidic amino acid, imidazole groups of histidine residue, amino groups of lysine residue, and indole group of tryptophan were essential for the activity of enzyme.

Studies on the chemical modification of the essential groups of N-Acetyl-beta-D-glucosaminidase from viscera of green crab (Scylla Serrata)

The chemical modification of N-acetyl-beta-D: -glucosaminidase (EC3.2.1.30) from viscera of green crab (Scylla serrata) has been first studied. The modification of indole groups of tryptophan of the enzyme by N-bromosuccinimide can lead to complete inactivation, accompanying the absorption decreasing at 275 nm and the fluorescence intensity quenching at 338 nm, indicating that tryptophan is essential residue to the enzyme. The modification of histidine residue, the carboxyl groups, and lysine residue inactivates the enzyme completely or incompletely. The results show that imidazole groups of histidine residue or sulfhydryl residues, the carboxyl groups of acidic amino acid, amino groups of lysine residue, and indole groups of tryptophan were essential for the catalytic activity of enzyme, while the results demonstrate that the disulfide bonds and the carbamidine groups of arginine residues are not essential to the enzyme's function.

Inhibitory kinetics of bromacetic acid on beta-N-acetyl-D-glucosaminidase from prawn (Penaeus vannamei)

beta-N-Acetyl-D-glucosaminidase (NAGase, EC.3.2.1.52), a composition of chitinases, cooperates with endo-chitinase and exo-chitinase to disintegrate chitin into N-acetylglucosamine (NAG). NAGase from prawn (Penaeus vannamei) is involved in digestion and molting processes. The investigation of enzymatic properties, functional groups and catalytic mechanism is an essential mission to its commercial application. Bromacetic acid (BrAc) is a specific modifier for the histidine residue in specific condition. In this paper, the effect of BrAc on prawn NAGase activity for the hydrolysis of pNP-NAG has been investigated. The results showed that BrAc can reversibly and non-competitively inhibit the enzyme activity at appropriate concentrations and the value of IC(50) was estimated to be 17.05+/-0.65 mM. The inhibition kinetics of the enzyme by BrAc has been studied using the kinetic method of the substrate reaction. And the inhibition model was set up and the microscopic rate constants for the reaction of the inhibitor with free enzyme and the enzyme-substrate complexes were determined for inactivation and reactivation. The rate constant of the forward inactivation (k(+0)), which is 1.25 x 10(-3)s(-1), is about eight times as much as that of the reverse reactivation (k(-0)), which is 1.64 x 10(-4)s(-1). Therefore, when the BrAc concentration is sufficiently large, the enzyme is completely inactivated.

Effects of Magnesium Ions on Thermal Inactivation of Alkaline Phosphatase

The effect of Mg2+ on the thermal inactivation and unfolding of calf intestinal alkaline phosphatase has been studied at different temperatures and Mg2+ concentrations. Increasing the Mg2+ concentration in the denatured system significantly enhanced the inactivation and unfolding of the enzyme during thermal inactivation. The analysis of the kinetic course of substrate reaction during thermal inactivation showed that at 47 degrees C the increased free Mg2+ concentration caused the inactivation rate to increase. Increasing the temperature strengthened the effect of Mg2+ on the thermal inactivation. Control experiment showed that this is not due to salt effect. The time course of fluorescence emission spectra showed that the emission maximum for Mg2+-containing system was always higher than that of Mg2+-free system, and the higher temperature enhanced this difference. In addition, Mg2+ also enhanced the unfolding rate of the enzyme at 47 degrees C. The potential biological significance of these results are discussed.

Effect of thiohydroxyl compounds on tyrosinase: inactivation and reactivation study

An unusual thioether bridge (Cys-His) has been detected at the active site of mushroom tyrosinase, and the effects of thiohydroxyl compounds such as dithiothreitol (DTT) and beta-mercaptoethanol (beta-ME) on Cu2+ at the active site have been elucidated. Treatment with DTT and beta-ME on mushroom tyrosinase completely inactivated 3,4-dihydroxyphenylalanine oxidase activity in a dose-dependent manner. Sequential kinetic studies revealed that DTT and beta-ME caused different mixed-type inhibition mechanisms: the slope-parabolic competitive inhibition (Ki = 0.143 mM) by DTT and slope-hyperbolic noncompetitive inhibition (Ki = 0.0128 mM) by beta-ME, respectively. Kinetic Scatchard analysis consistently showed that mushroom tyrosinase had multiple binding sites for DTT and beta-ME with different affinities. Reactivation study of inactivated enzyme by addition of Cu2+ confirmed that DTT and beta-ME directly bound with Cu2+ at the active site. Our results may provide useful information regarding interactions of tyrosinase inhibitor for designing an effective whitening agent targeted to the tyrosinase active site.

Refolding and reactivation of calf intestinal alkaline phosphatase with excess magnesium ions

It is well known that Mg(2+) is an essential component in many biological processes. This research investigated the courses of both the reactivation and the refolding in the absence and presence of Mg(2+) ions. Calf intestinal alkaline phosphatase (CIP) was extensively denatured in 3 M guanidine hydrochloride (GdnHCl) solution for 2 h. Under suitable renaturation conditions, about 60-70% of the activity was recovered in the absence and presence of different magnesium ion concentrations. The refolding processes followed two-phase courses, whereas the reactivation processes were monophasic after dilution in proper solutions with or without Mg(2+). The magnesium ions affected both the reactivation and the refolding courses of unfolded CIP. A comparison of rate constants for the refolding of unfolded CIP with those for recovery of enzyme activity at different Mg(2+) concentrations showed that they were not synchronized. The activity recovery was speeded up due to the presence of Mg(2+) ions; while the refolding course of unfolded CIP was somewhat inhibited by the excess Mg(2+).