Spectroscopy and molecular docking study on the interaction of daidzein and genistein with pepsin

The interaction of pepsin with daidzein (Dai) or genistein (Gen) was investigated using spectroscopic techniques under simulated physiological conditions. Dai and Gen can quench the fluorescence of pepsin and the quenching mechanism was a static process. The binding site number n and apparent binding constant K were measured at different temperatures. The thermodynamic parameters ΔΗ, ΔG and ΔS were calculated. The results indicated that van der Waals forces and hydrogen bond formation played major roles in the interaction of Dai or Gen with pepsin. The binding distance between pepsin and Dai or Gen was calculated according to energy transfer theory. The results of synchronous fluorescence spectra showed that the microenvironment and conformation of pepsin were changed. UV absorption and 3D fluorescence spectra showed that the binding interaction disturbed the microenvironment of amino acid residues and induced conformational changes in pepsin. Molecular docking results showed that Dai and Gen entered into the hydrophobic cavity of pepsin and two hydrogen bonds formed between Dai or Gen and pepsin. The results demonstrated that the interaction behavior between Dai and Gen with pepsin was slightly different, which denoted that the 5‐hydroxyl group of Gen, to a certain extent, had an effect on ligand binding to proteins. Copyright © 2016 John Wiley & Sons, Ltd.     

Fluorescence spectroscopic analysis on interaction of fleroxacin with pepsin

The interaction between fleroxacin (FLX) and pepsin was investigated by spectrofluorimetry. The effects of FLX on pepsin showed that the microenvironment of tryptophan residues and molecular conformation of pepsin were changed based on fluorescence quenching and synchronous fluorescence spectroscopy in combination with three‐dimensional fluorescence spectroscopy. Static quenching was suggested and it was proved that the fluorescence quenching of pepsin by FLX was related to the formation of a new complex and a non‐radiation energy transfer. The quenching constants K_SV, binding constants K and binding sites n were calculated at different temperatures. The molecular interaction distance (r = 6.71) and energy transfer efficiency (E = 0.216) between pepsin and FLX were obtained according to the Forster mechanism of non‐radiation energy transfer. Hydrophobic and electrostatic interaction played a major role in FLX–pepsin association. In addition, the hydrophobic interaction and binding free energy were further tested by molecular modeling study. Copyright © 2013 John Wiley & Sons, Ltd.     

Quantification of gastric secretions in the wild whiting fed on natural prey in captivity

Quantification of gastric acid and enzyme pepsin in the gastric phase of digestion in wild whiting (Merlangius merlangus L.) were elucidated in the present study. The results showed that after ingestion of a meal, first pepsin and, more slowly, gastric acid (hydrochloric acid) was secreted into the gastric lumen to peak at 2–4 h (49.4–53.8 mEq wt acid × 10³; 652–813 μg pepsin ml Eq min^?1). Fish size had a significant influence on the amount of gastric acid and pepsin secreted; digestive power increased α W^0.67, as predicted by the ‘physiological’ model. However, the predicted effects of meal size [stimulus, distension volume (DV)] were not clear. Instead, the stomach distension model for flatfish from a previous worker showed that muscular contractions (mixing mechanism) were related to DV^0.33 and found to partially support the physiological model in the present study.     

Gastric antibacterial efficiency is different for pepsin A and C

The gastric lumen represents a bactericidal barrier, whose major components are an acidic pH and a family of isoenzymes of the gastric aspartate protease, pepsin. To evaluate whether specific pepsins are specialized in antibacterial protection, we tested their effects on the gastric pathogen Helicobacter pylori. In a recent study we found pepsin to affect the motility of the bacteria, one of its most important virulence factors. We were able to show that the antibacterial effect of pepsin occurs in two phases: rapid loss of motility and subsequent destruction. In the present study we used the rapid pepsin-induced bacterial immobilization as a marker of antibacterial efficiency. The proteolytic activity of different pepsins was normalized to values between 2 and 200 U/ml in the hemoglobin degradation test of Anson, performed at pH 2 and 5. We found that pepsin C completely inactivates H. pylori at proteolytic activities of 2 (pH 5) and 20 (pH 2) U/ml. In contrast, the activities of pepsin A and chymosin required to affect Helicobacter motility were ten times higher.     

THE PROTEIN COMPOSITION OF NUCLEAR CRYSTALS IN LEAF CELLS

The chemical composition of perinuclear crystals of Lychnis chalcedonica and intranuclear crystals of Dianthus barbatus in leaf tissue embedded in glycol methacrylate was tested by differential enzyme digestion of ultra-thin sections. The Lychnis crystals were digested readily by pepsin but with great difficulty and never to completion by trypsin. The Dianthus crystals were rapidly and completely digested by pronase; inconsistently and with difficulty by pepsin; and were unaffected by trypsin. Pre-incubation with water increased the effectiveness of pepsin digestion. Neither RNase nor DNase had any effect, either alone, or when preceded or followed by the proteinases. It was concluded that the Lychnis crystals are composed of protein that is probably high in aromatic amino acid content, and possibly low in the basic amino acids arginine and lysine. The Dianthus crystals also seem to be protein, but because of their amino acid composition or conformation, and possibly because of complex reactions with the fixative, these crystals are not readily hydrolyzed by pepsin and trypsin.     

The influence of Al3+ ion on porcine pepsin activity in vitro

The in vitro effect of Al³⁺ ions in the concentration range 1.7·10^{? 6} M–8.7·10^{? 3} M on pepsin activity at pH 2, via kinetic parameters and its electrophoretic mobility was evaluated. Kinetic study demonstrated the existence of an activation effect of Al³⁺ at pH 2 on pepsin molecule. Kinetic analysis with respect to concentrations of haemoglobin showed that Al³⁺ ions increase the maximal velocity (V_max) and k_cat values rather than apparent affinity for substrate (K_S) implying the non-competitive nature of activation which indicated that aluminium was a non-essential activator of partial non-competitive type. The values of the equilibrium constants K_S and K_mA for dissociation of corresponding complexes were evaluated as 0.904 ± 0.083 mM and 8.56 ± 0.51 μM, respectively. Dissociation constant K_A, of activator from enzyme-activator complex calculated via kinetic and direct measurement of Al³⁺ binding data, as well as activation constant A₅₀, the activator concentration that gives a rate equal to half at a saturating concentration of activator, were found to be 8.82 ± 0.90 μM, 8.39 ± 0.76 μM, and 8.05 ± 0.48 μM respectively. Native PAGE electrophoresis shows the decrease in electrophoretic mobility of pepsin and confirms modification of the electric charge and conformational changes of pepsin caused by bound Al³⁺ on the pepsin molecule. Al³⁺ induced conformational changes of pepsin were verified by UV-VIS and IR spectra. Moreover, the absence of conformational changes in the haemoglobin molecule in the presence of Al³⁺ ions confirms that the obtained activation is a consequence of conformational changes caused only in the pepsin molecule.     

Debittering effect of Monascus carboxypeptidase during the hydrolysis of soybean protein

The actions of pepsin and the admixture of pepsin and Monascus pilosus carboxypeptidase 1 (MpiCP-1) on the hydrolysis of soybean protein were studied. The results showed that the pepsin hydrolyzate of soybean protein was much more bitter and contained relatively smaller amounts of total free amino acids than the hydrolyzate obtained with the admixture of pepsin and MpiCP-1. In addition, hydrophilic and hydrophobic amino acids were present in almost equal proportions in the pepsin hydrolyzate, while mainly hydrophobic amino acids made up the hydrolyzate obtained with the admixture of pepsin and MpiCP-1. These results suggest that MpiCP-1 suppresses and reverses the development of the bitterness taste that results from the pepsin hydrolysis of soybean protein by releasing mainly hydrophobic amino acids from the C-termini of the bitter components.     

The C-terminal extrahelical peptide of type I collagen and its role in fibrillogenesis in vitro

The formation in vitro of fibrils from type I acid-soluble calf skin collagen has been studied before and after removal of the extrahelical peptides with carboxypeptidase and with pepsin. Turbidimetric studies show that the mechanism of fibril growth in undigested collagen is similar to that in pepsin-digested collagen; following carboxypeptidase digestion, however, a different growth mechanism was apparent. The two mechanisms have been further characterized by electron microscopy. In the course of formation of fibrils from undigested collagen, “early fibrils” (short D-periodic fibrils that have both ends visible) occurred in the lag phase under the precipitating conditions employed here. After pepsin or carboxypeptidase digestion of the collagen no “early fibrils” were seen. In carboxypeptidase-digested collagen, lateral assembly was inhibited; after pepsin digestion, linear assembly was inhibited. Complete removal of the extrahelical peptides prevented fibril formation under the conditions used here. Electron-optical examination of segment-long-spacing (SLS) dimers established a more complete removal of the C-terminal peptide after carboxypeptidase digestion than after pepsin digestion. Analyses of staining patterns of SLS dimers and fibrils from undigested and digested samples showed that the C-terminal peptide in SLS crystallites and fibrils formed from undigested collagen is in a condensed conformation. A proposed conformation, in which condensation occurs predominantly in a hydrophobic region at the proximal end of the C-terminal peptide, is discussed in terms of a dual role for the C-terminal peptide in fibrillogenesis. One role, shared with the N-terminal peptide, is to participate in interactions between the 4D-staggered molecules leading to the formation of linear aggregates; the other is to participate in interactions between these linear aggregates giving rise to D-periodic aggregates and lateral (as well as linear) growth.     

Synergistic antidigestion effect of <Emphasis Type="Italic">Lactobacillus rhamnosus</Emphasis> and bovine colostrums in simulated gastrointestinal tract (in vitro)

Probiotics and bovine colostrums had been proven to be beneficial for human health. Lactobacillus rhamnosus ZDY114 and anti-Helicobacter pylori bovine colostrums were used for the preparation of microecological additives, and their synergistic antidigestion effect in the simulated gastrointestinal tract (in vitro) was investigated. Either L. rhamnosus or purified IgG from immune colostrums was very sensitive in simulated gastric environment and slightly sensitive in simulated intestinal tract. No viable counts were recovered from the solution of dissolved freeze-dried powder (7.14 log₁₀ CFU/ml) of L. rhamnosus when digested at pH 3.0 with pepsin for 30 min. Activity of purified IgGs from immune colostrums could not be detected when digested at pH 3.0 with pepsin for 30 min; 29% titer could be detected when digested at pH 8.0 with trypsin for 5 h. The IgGs in nonpurified immune colostrums presented stronger resistance against gastrointestinal digestion than purified IgGs. Moreover, the combination of L. rhamnosus ZDY114 and immune colostrums strengthened their antidigestion ability. Even under pH 3.0, 4.0 with pepsin, the titer of anti-HP IgG maintained above 123 and 83.3%, respectively. Similarly, that titer was above 93.3% when digested at pH 8.0 with trypsin for 4.5 h. In conclusion, L. rhamnosus and anti-Helicobacter pylori bovine colostrums had synergistic antidigestion effect in simulated gastrointestinal tract (in vitro).     

Effects of Angiotensin I-Converting Enzyme Inhibitory Substances Derived from Indonesian Dried-salted fish on Blood Pressure of Rats

Indonesian dried-salted fish (DSF) was produced from skipjack tuna by soaking the flesh in 15% NaCl (DSF I) or 25% NaCl (DSF II). The DSFs were then hydrolyzed by trypsin, chymotrypsin, Pronase E, and pepsin. Angiotensin I-converting enzyme (ACE) inhibitory activity was measured. The pepsin digest showed the highest inhibitory activity (IC₅₀; 0.63 mg protein/ml). DSF II hydrolysate had higher inhibitory activity than that in DSF I. A three-month storage period of DSF gave higher ACE-inhibitory activity than that of 6 months. An oral administration of pepsin hydrolysate significantly decreased the blood pressure of rats. From the purification steps, at least 4 inhibitor peptides were found. The amino acid sequences of the peptides were Val-Ala-Trp-Lys-Leu, Trp-Ser-Lys-Val-Val-Leu, Ser-Lys-Val-Pro-Pro, and Cys-Trp-Leu-Pro-Val-Tyr, with an IC₅₀ value of 31.97, 156.28, 74.22, and 22.20 μM, respectively.     

Some Physicochemical Properties and Substrate Specificity of Acid Protease of Rhodotorula glutinis K-24

Some physicochemical properties, amino acid composition, and substrate specificity of the acid protease of Rhodotorula glutinis K-24 were determined. The molecular weight was estimated to be about 30,000 by the sedimentation equilibrium method. This value also coincided with the data obtained from Andrews’s method.

The isoelectric point was pH 4.5, and the amino terminal amino acid was identified to be alanine. The enzyme contained 14.5% of nitrogen and was composed of 285 residues of amino acid. Substrate specificity toward synthetic peptides was similar to that of pepsin, but its activity was considerably weak.

The enzyme was inactivated by diazoacetyl glycine ethylester, p-bromophenacyl bromide, et al., which attacked the active center of pepsin.     

Physicochemical characterization of an aspin (rBm-33) from a filarial parasite Brugia malayi against the important human aspartic proteases

The aspartic protease inhibitory efficiency of rBm-33, an aspin from a filarial parasite Brugia malayi was investigated. rBm-33 was found to be thermostable up to 90°C and it forms a stable ‘enzyme-product’ complex with human pepsin. Aspartic protease inhibitory activity was investigated using UV spectroscopy and isothermal titration calorimetry. Our results suggest that rBm-33 inhibits the activity of important human aspartic proteases that were examined with binding constants (K_b) values between 10.23?×?10³ and 6.52?×?10³ M^?1. The binding reactions were enthalpy driven with ΔH_b values between ?50.99 and ?46.07 kJ mol^?1. From kinetic studies, pepsin inhibition by rBm-33 was found to be linear competitive with an inhibition constant (Ki) of 2.5 (±0.8) nM. Because of the inhibitory efficacy of Bm-33 against important human aspartic proteases which play a vital role in immune-regulation along with other functions, Bm-33 can be projected as a drug target for the filariasis.     

Studies on the Proteolytic Enzymes of Black Aspergilli

The specificity of crystalline Asp. Saitoi proteinase on oxidized lysozyme has been investigated by application of the Sanger DNP-method.

It was found that this proteinase has a much broader specificity as compared with pepsin and Bac. subtilis proteinase.     

Process integration for recovery of recombinant collagen type I α1 from corn seed

Because of safety concerns and product consistency issues with the use of animal‐derived collagen, several recombinant protein expression hosts have been considered for recombinant collagen corn seed. Full length, triple‐helical, recombinant collagen (rCIα1) is expressed as a fusion with a foldon domain, which must later be removed. Here we have examined integration of purification and foldon removal by comparing advantages of removal before or after purification, using salt precipitation as the main purification step. Because expression levels in available maize lines are low, Pichia‐produced recombinant collagens, both with and without foldon, were added to corn seed germ at the extraction step. Salt precipitation of an acidic corn seed extract yielded 100% of the collagen without foldon at >70% purity without the pepsin pretreatment. With pepsin pretreatment, yield was 94.0% with purity of 76.5%. Analysis of the protein molecular weight distribution of the pre‐ and post‐treatment extracts showed that the corn proteins are largely resistant to pepsin proteolysis, explaining why little benefit was obtained by pepsin treatment. In the absence of pepsin treatment, the recovery of rCIα1 with foldon was still above 90% but the purity was only 44%. This still represented at about 13‐fold purification with a 2.7‐fold volume reduction which would reduce the pepsin requirement for post‐recovery foldon cleavage. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 32:98–107, 2016     

The vegetable rennet of Cynara cardunculus L. contains two proteinases with chymosin and pepsin-like specificities

The flowers of cardoon (genus Cynara) are traditionally used in Portugal for cheese making. In this work the vegetable rennet of the species Cynara cardunculus L. was characterized in terms of enzymic composition and proteolytic specificity of its proteinases (cardosin A and cardosin B). Cardosin A was found to cleave insulin B chain at the bonds Leu15-Tyr16, Leu17-Val18 and Phe25-Tyr26. In addition to the bonds mentioned cardosin B cleaves also Glu13-Ala14, Ala14-Leu15 and Phe24-Phe25 indicating that it has a broader specificity. The kinetic parameters for the hydrolysis of the synthetic peptide Leu-Ser-Phe(NO₂)-Nle-Ala-Leu-oMe were also determined and compared to those of chymosin and pepsin. The results obtained indicate that in terms of specificity and kinetic parameters cardosin A is similar to chymosin whereas cardosin B is similar to pepsin. It appears therefore that the enzyme composition of cardoon rennet closely resembles that of calf rennet.     

Gating of a voltage-dependent channel (colicin E1) in planar lipid bilayers: the role of protein translocation

Summary The voltage-dependent channel formed in planar lipid bilayers by colicin E1, or its channel-forming C-terminal fragments, is susceptible to destruction by the nonspecific protease pepsin under well-defined conditions. In particular, pepsin acts only from thecis side (the side to which colicin has been added) and only upon channels in the closed state. Channels in the open state are refractory to destruction bycis pepsin, and neither open nor closed channels are destroyed bytrans pepsin. Colicin E1 channels are normally turned on bycis positive voltages and turned off bycis negative voltages. For large (>80 mV) positive voltages, however, channels inactivate subsequent to opening. Associated with the inactivated state, some channels become capable of being turned on bycis negative voltages and turned off bycis positive voltages, as if the channel-forming region of the molecule has been translocated across the membrane. Consistent with this interpretation is the ability now oftrans pepsin to destroy these reversed channels when they are closed, but not when they are open, whereascis pepsin has no effect on them in either the open or closed state. Our results indicate that voltage gating of the E1 channel involves translocation of parts of the protein across the membrane, exposing different domains to thecis andtrans solutions in the different channel states.     

Study on the binding of chlorogenic acid to pepsin by spectral and molecular docking

The interaction of pepsin with chlorogenic acid (CHA) was investigated using fluorescence, UV/vis spectroscopy and molecular modeling methods. Stern–Volmer analysis indicated that the fluorescence quenching of pepsin by CHA resulted from a static mechanism, and the binding constant was 1.1846 × 10⁵ and 1.1587 × 10⁵ L/mol at 288 and 310 K, respectively. The distance between donor (pepsin) and acceptor (CHA) was calculated to be 2.39 nm and the number of binding sites for CHA binding on pepsin was ~ 1. The results of synchronous fluorescence and three‐dimensional fluorescence showed that binding of CHA to pepsin could induce conformational changes in pepsin. Molecular docking experiments found that CHA bonded with pepsin in the area of the hydrophobic cavity with Van der Waals' forces or hydrogen bonding interaction, which were consistent with the results obtained from the thermodynamic parameter analysis. Furthermore, the binding of CHA can inhibit pepsin activity in vitro. Copyright © 2013 John Wiley & Sons, Ltd.     

Interaction between caffeic acid phenethyl ester and protease: monitoring by spectroscopic and molecular docking approaches

The interaction of one anticancer drug (caffeic acid phenethyl ester; CAPE) with three proteases (trypsin, pepsin and α-chymotrypsin) has been investigated with multispectral methods and molecular docking. As an active components in propolis, the findings are of great benefit to metabolism, design, and structural modification of drugs. The results show that CAPE has an obvious ability to quench the trypsin, pepsin, or α-chymotrypsin fluorescence mainly through a static quenching procedure. Trypsin has the largest binding affinity to CAPE, and α-chymotrypsin has the smallest binding affinity to CAPE. The data obtained from thermodynamic parameters and molecular docking prove that the spontaneously interaction between CAPE and each protease is mainly due to a combination of van der Waals (vdW) force and hydrogen bond (H-bond), controlled by an enthalpy-driven process. The binding force, strength, position, and the number of H-bond are further obtained from the results of molecular docking. Through ultraviolet spectroscopy, dynamic light scattering and circular dichroism experiments, the change in the protease secondary structure induced by CAPE was observed. Additionally, the addition of protease had a positive effect on the antioxidative activity of CAPE, and α-chymotrypsin has the greatest effect on the removal of 2,2-diphenyl-1-picrylhydrazyl free radicals by CAPE.     

Digestive enzyme activity of the Japanese grenadier anchovy Coilia nasus during spawning migration: influence of the migration distance and the water temperature

In this study, we investigated the activity levels of two major digestive enzymes (pepsin and lipase) in the commercially important Japanese grenadier anchovy Coilia nasus during its upstream migration to analyse the digestive physiological responses to starvation and to analyse the influence of the water temperature on enzyme activity. Water temperature had a significant effect on pepsin activity, while long-term starvation resulted in a significant decrease in pepsin activity. As starvation continued, however, a slight increase in pepsin activity between the Wuhu (440 river km) and Anqing (620 river km) regions may indicate that C. nasus had refeeding behaviour due to its large expenditure of energy reserves. In contrast, lipase activity was not significantly affected by the water temperature but the effect of fasting increased as much as 13% of lipase activity from the Chongming region (20 river km) to Anqing region, suggesting that the stored lipids of grenadier anchovy were mobilised to meet energy requirements of upstream migration activity and gonad development. Lipid mobilisation activated lipoprotein lipase (LPL; proteins with lipase activity) to hydrolyse triacylglycerides (TAG), which is the first step of lipid assimilation and obtained energy from fatty acids under fasting conditions. Therefore, the increased lipase activity is attributed mainly to the lipase that is involved in endogenous lipid hydrolysis. Grenadier anchovy appears to adapt to long-term starvation during migration and the increased lipase activity may indicate a crucial effect on lipid metabolism. This study demonstrated that distinct alterations occur in pepsin and lipase activities during the spawning migration of grenadier anchovy due to exogenous nutrition and endogenous metabolism. Furthermore, it provides a basis for further research on the digestive physiology and energy metabolism in this species.     

Protease inhibitors from Streptomyces violascens

Summary Two protease inhibitors from the culture fluid of Streptomyces violascens U 10600 have been purified with a method including freeze-drying, methanol extraction, dialysis, and ultrafiltration. By gel filtration on Sephadex G-15 a separation in two active inhibitors, one of trypsin and one of chymotrypsin, was made.The inhibitors were stable at 100°C, pH 5, for 20 min and at 24°C between pH 1.8 to 9.7. Both inhibitors were dialysable. They had no bacteriostatic or fungistatic effects. The trypsin inhibitor inhibited also papain and proteases from Aspergillus oryzae, Alternaria tenuissima, Entomophthora coronata, and to some extent Gibberella fujikuroi, but not chymotrypsin, kallikrein, ficin, or pepsin. The chymotrypsin inhibitor inhibited also papain and proteases from Aspergillus oryzae, Alternaria tenuissima, and Gibberella fujikuroi, but not trypsin, kallikrein, ficin, pepsin, or protease from Entomophthora coronata.