Study of the action of human salivary alpha-amylase on 2-chloro-4-nitrophenyl alpha-maltotrioside in the presence of potassium thiocyanate

Biochemical and Phylogenetic Analysis of Italian Phaseolus vulgaris Cultivars as Sources of α-Amylase and α-Glucosidase Inhibitors

Phaseolus vulgaris α-amylase inhibitor (α-AI) is a protein that has recently gained commercial interest, as it inhibits mammalian α-amylase activity, reducing the absorption of dietary carbohydrates. Numerous studies have reported the efficacy of preparations based on this protein on the control of glycaemic peaks in type-2 diabetes patients and in overweight subjects. A positive influence on microbiota regulation has also been described. In this work, ten insufficiently studied Italian P. vulgaris cultivars were screened for α-amylase- and α-glucosidase-inhibiting activity, as well as for the absence of antinutritional compounds, such as phytohemagglutinin (PHA). All the cultivars presented α-glucosidase-inhibitor activity, while α-AI was missing in two of them. Only the Nieddone cultivar (ACC177) had no haemagglutination activity. In addition, the partial nucleotide sequence of the α-AI gene was identified with the degenerate hybrid oligonucleotide primer (CODEHOP) strategy to identify genetic variability, possibly linked to functional α-AI differences, expression of the α-AI gene, and phylogenetic relationships. Molecular studies showed that α-AI was expressed in all the cultivars, and a close similarity between the Pisu Grogu and Fasolu cultivars' α-AI and α-AI-4 isoform emerged from the comparison of the partially reconstructed primary structures. Moreover, mechanistic models revealed the interaction network that connects α-AI with the α-amylase enzyme characterized by two interaction hotspots (Asp38 and Tyr186), providing some insights for the analysis of the α-AI primary structure from the different cultivars, particularly regarding the structure-activity relationship. This study can broaden the knowledge about this class of proteins, fuelling the valorisation of Italian agronomic biodiversity through the development of commercial preparations from legume cultivars.

Actinidin diversity: discovery of common and selective substrates for actinidin isoforms and Actinidia cultivars

The actinidin proteinase family has a striking sequence diversity; isoelectric points range from 3.9 to 9.3. The biological drive for this variation is thought to be actinidin's role as a defense-related protein. In this study we map mutations in the primary sequence onto the 3D structure of the protein and show that the region with the highest diversity is close to the substrate binding groove. Non-conservative substitutions in the active site determine substrate preference and therefore create problems for quantification of actinidin activity. Here we use a peptide substrate library to compare two actinidin isoforms, one from the kiwiberry cultivar 'Hortgem Tahi' (Actinidia arguta), and the other from the familiar kiwifruit cultivar 'Hayward' (Actinidia chinensis var. deliciosa). Among 360 octamer substrates we find one substrate (RVAAGSPI) with the useful property of being readily cleaved by all the functionally active actinidins in a set of A. arguta and A. chinensis var. deliciosa isoforms. In addition, we find that two substrates (LPPKSQPP & ILRDKDNT) have the ability to differentiate different isoforms from a single fruit. We compare actinidins from 'Hayward' and A. arguta for their ability to digest the allergenic gluten peptide (PFPQPQLPY) but find the peptide to be indigestible by all sources of actinidin. The ability to inactivate salivary amylase is shown to be a common trait in Actinidia cultivars due to proteolysis by actinidin and is particularly strong in 'Hortgem Tahi'. A mixture of 10% 'Hortgem Tahi' extract with 90% saliva inactivates 100% of amylase activity within 5 minutes. Conceivably, 'Hortgem Tahi' might lower the glycaemic response in a meal rich in cooked starch.

Genomic sequencing of Gracilibacillus dipsosauri reveals key properties of a salt-tolerant α-amylase

Gracilibacillus dipsosauri is a moderately-halophilic Gram-positive bacterium which forms an extracellular α-amylase that is induced by starch, repressed by D-glucose, and active in 2.0 M KCl. Previous studies showed that while enzyme activity could be measured with the synthetic substrate 2-chloro-4-nitrophenyl-α-D-maltotrioside (CNPG3), other assays were inconsistent and the protein showed aberrant mobility during nondenaturing gel electrophoresis. To clarify the properties of this enzyme, the genome of G. dipsosauri was sequenced and was found to be 4.19 Mb in size with an overall G+C content of 36.9%. A gene encoding an α-amylase composed of 691 amino acids was identified. The protein was a member of the glycosyl hydrolase 13 family, which had a molecular mass of 77,396 daltons and a pI of 4.39 due to an unusually large number of aspartate and glutamate residues (95/691 or 13.7%). BLAST analysis of the amino acid sequence revealed significant matches to other proteins with cyclodextrin glycosyltransferase activity. Partial purification of the protein from G. dipsosauri showed that fractions catalyzing the hydrolysis of CNPG3 and p-nitrophenyl-D-maltoheptoside also catalyzed the formation of β-cyclodextrin but not α-cyclodextrin or γ-cyclodextrin. Formation of β-cyclodextrin was not stimulated by high salt concentrations but did occur with rice, potato, wheat, and corn starches and amylopectin. These studies explain the unusual features of the α-amylase from G. dipsosauri and indicate it should be classified as EC 2.4.1.19. The availability of the complete genomic sequence of G. dipsosauri will provide the basis for studies on other enzymes from this halophile which may be useful for biotechnology.

Colorimetric Detection of Salivary α-Amylase Using Maltose as a Noncompetitive Inhibitor for Polysaccharide Cleavage

This paper describes an approach for colorimetric detection of salivary α-amylase, one of the potential biomarkers of autonomic nervous system (ANS) activity, for enabling assessment of fatigue. The ability of α-amylase to cleave α-bonds of polysaccharides is utilized for developing a colorimetric assay. In the proposed approach, 2-chloro-4-nitrophenyl-α-d-maltotrioside as substrate releases a colored byproduct upon cleavage by salivary α-amylase. Introduction of maltose as a noncompetitive inhibitor yields desirable linear responses in the physiologically relevant concentration range (20-500 μg/mL) with a limit of detection (LOD) of 8 μg/mL (in aqueous solution). The concentrations of substrate and noncompetitive inhibitor are subsequently optimized for colorimetric detection of salivary α-amylase. A facile paper-based "strip" assay is proposed for analysis of human saliva samples with marginal interference from saliva components. The proposed assay is rapid, specific, and easy-to-implement for colorimetric detection of salivary α-amylase between 20 and 500 μg/mL. Complementary RGB (red, green, blue components) analysis offers quantitative detection with a LOD of 11 μg/mL. The two assay formats are benchmarked against the Phadebas test, a state of the art method for spectrophotometric detection of α-amylase. The reported paper-based methodology possesses a high potential for estimation of altered ANS responses toward stressors that possibly could find applications in assessment of fatigue and for monitoring onset of fatigue.

Kiwifruit actinidin digests salivary amylase but not gastric lipase

Kiwifruit contains the cysteine proteinase actinidin whose strong activity allows kiwifruit to be used as a meat tenderiser. This raises the possibility digestive enzymes, also proteins, are themselves susceptible to degradation by actinidin. Salivary amylase and gastric lipase are exposed to the highest concentrations of actinidin whereas duodenal enzymes are less likely to be inactivated by actinidin due to dilution and inactivation of actinidin by gastric juice. The saliva of six volunteers was exposed to Actinidia deliciosa homogenate and then examined for loss of the starch digesting enzyme, alpha-amylase. In agreement with the known distribution of salivary amylase concentration in saliva, the range of amylase activity within the group of volunteers varied by around 100 fold. Within 5 minutes of incubation of 3 parts saliva to one part green kiwifruit at 37 °C, approximately 85% of the amylase activity was lost. The use of E-64, a selective inhibitor of cysteine proteinases, confirmed that the loss of amylase function was due to actinidin. Amylase protein degradation was followed by SDS-PAGE and western blotting. Recombinant human gastric lipase resisted digestion with kiwifruit even after 30 minutes incubation and remained functionally active after this time period. However, both mountain papaya and pineapple extracts degraded gastric lipase fully during a 30 minutes digestion period. Under conditions where cooked starch is consumed along with kiwifruit it is possible that starch digestion may be retarded whereas lipid digestion in the stomach is unlikely to be affected by kiwifruit consumption.

[Functional endoscopy : the physiological and pathophysiological basis of reflux disease, diagnosis and therapy]

ENT specialists and gastroenterologists are increasingly confronted with the question of how to recognize and evaluate extra-esophageal complications of reflux. Both specialities need to collaborate, since they are connected via the esophagus, and both need to know more about the speciality of their neighbor than was hitherto usual. This publication presents the observations and measurements of little-known physiological functions. This is followed by an attempt to define the border between healthy and diseased. Finally, the possible consequences of functional disorders are described. The leap from observation of function to the microcosm of biochemical links is discussed and supported using experimental work. This overview highlights the limitations of our current knowledge. The success of functional endoscopy in terms of therapeutic approaches is immense. The required therapy is finally based on a clear diagnostic concept; probatory therapy is a waste of money.

Accurate quantitation of salivary and pancreatic amylase activities in human plasma by microchip electrophoretic separation of the substrates and hydrolysates coupled with immunoinhibition

A high-performance determination system for alpha-amylase isoenzyme activities in human plasma involving microchip electrophoresis with a plastic chip was developed. The combination of microchip electrophoresis for substrate and hydrolysate separation and an immunoinhibition method for the differentiation of isoenzyme activities using antihuman salivary amylase (S-AMY) mAb allowed the highly selective determination of amylase isoenzyme (S-AMY and pancreatic amylase (P-AMY)) activities even in a complex matrix such as a crude plasma sample. We used 8-aminopyrene-1,3,6-trisulfonic acid (APTS)-labeled maltohexaose (G6) as a substrate. Amylase in a human plasma sample hydrolyzed APTS-G6 into APTS-maltotriose (G3) and G3, which was measured as the fluorescence intensity of APTS-G3 on microchip electrophoresis. A double logarithm plot revealed a linear relationship between amylase activity and fluorescence intensity in the range of 5-500 U/L of amylase activity (r2=0.9995, p<0.01), and the LOD was 4.38 U/L. Amylase activities in 13 subjects determined by the present method were compared with the results obtained by conventional methods with nitrophenylated oligosaccharides as substrates, respectively. Good correlations were observed for each method on simple linear regression analysis (both p<0.01). The reproducibilities of within-days for total amylase and P-AMY were 2.98-6.27 and 3.83-6.39%, respectively, and these between-days were 2.88-5.66 and 3.64-5.63%, respectively. This system enables us to determine amylase isoenzyme activities in human plasma with high sensitivity and accuracy, and thus will be applicable to clinical diagnosis.

An ideal substrate for the measurement of pancreatic amylase?

The advanced knowledge on substrate cleavage by human alpha-amylases promotes the development of chromogenic maltotriosides exclusively cleaved at the aglycone bond. Three essentials are required for this type of binding at the active site of the enzyme: (i) A minimal hydrophobic modification at the ultimate glucose unit to exclude the condensation of reaction products, (ii) a non-ionic substituent in the 2-position of the phenolic chromophore, and (iii) pertinent effectors to accomodate the aglycone at subsite +1. The novel substrate 2-chloro-4-nitrophenyl-alpha-D-maltotrioside (acG3-CNP) is presented as an example together with measurement conditions which allow a direct, sensitive and specific measurement of pancreatic amylase without stoichiometric calculations.

Total and Pancreatic Amylase Measured with 2-Chloro-4-nitrophenyl-4-O-β-d-galactopyranosylmaltoside

Background: Many different methods have been used to assay amylase activity, using nitrophenylated oligosaccharides as substrate; however, the hydrolysis steps in these methods are complex.

Methods: We developed a new continuously monitoring assay for amylase activity in biological fluids, using 2-chloro-4-nitrophenyl-4-O-β-d-galactopyranosylmaltoside (GalG2CNP) as the substrate; this assay was used with anti-human salivary amylase monoclonal antibodies for specific determination of the pancreatic isoenzyme. Amylase converted GalG2CNP into β-d-galactopyranosylmaltose and 2-chloro-4-nitrophenol, which was measured at 405 nm.

Results: GalG2CNP was cleaved between 2-chloro-4-nitrophenol and β-d-galactopyranosylmaltose and did not undergo transfer reactions. The within-assay CVs (n = 20) for total amylase (T-AMY) and pancreatic amylase (P-AMY) were 0.6–1.6% and 0.5–2.5%, respectively; and day-to-day CVs (n = 10) for T-AMY and P-AMY were 0.8–3.7% and 0.6–4.1%, respectively. T-AMY and P-AMY activities in serum or urine obtained by the proposed method correlated well with those determined by the 2-chloro-4-nitrophenyl 4-O-β-d-galactopyranosyl-β-maltotetraoside method or the modified IFCC method.

Conclusions: This novel assay for T-AMY and P-AMY measures both activities stoichiometrically, directly, and easily, and may be suitable for routine procedures.

Amylose chain behavior in an interacting context. III. Complete occupancy of the AMY2 barley alpha-amylase cleft and comparison with biochemical data

In the first two papers of this series, the tools necessary to evaluate substrate ring deformations were developed, and then the modeling of short amylose fragments (maltotriose and maltopentaose) inside the catalytic site of barley alpha-amylase was performed. In this third paper, this docking has been extended to the whole catalytic cleft. A systematic approach to extend the substrate was used on the reducing side from the previous enzyme/pentasaccharide complex. However, due to the lack of an obvious subsite at the nonreducing side, an alternate protocol has been chosen that incorporates biochemical information on the enzyme and features on the substrate shape as well. As a net result, ten subsites have been located consistent with the distribution of Ajandouz et al. (E. H. Ajandouz, J. Abe, B. Svensson, and G. Marchis-Mouren, Biochimica Biophysica Acta, 1992, Vol. 1159, pp. 193-202) and corresponding binding energies were estimated. Among them, two extreme subsites (-6) and (+4), with stacking residues Y104 and Y211, respectively, have strong affinities with glucose rings added to the substrate. No other deformation has been found for the new glucose rings added to the substrate; therefore, only ring A of the DP 10 fragment has a flexible form when interacting with the inner stacking residues Y51. Global conservation of the helical shape of the substrate can be postulated in spite of its significant distortion at subsite (-1).

Evaluation of a direct alpha-amylase assay using 2-chloro-4-nitrophenyl-alpha-D-maltotrioside

We present the adaptation of an IFCC method for alpha-amylase using 2-chloro-4-nitro-phenyl-alpha-D-maltotrio-side as substrate (1) suited for routine work at 37 degrees C. In the assay, a constant proportion of substrate, i. e. 92%, is directly converted to 2-chloro-4-nitrophenol and maltotriose. The method is based on multi- and univariate optimization leading to following measurement conditions: substrate, 2.25 mmol/l; chloride, 310 mmol/l; calcium 5.0 mmol/l; 4-morpholinoethanesulphonic acid, 50 mmol/l; pH 6.28. The assay may be carried out manually or by mechanized procedures, with substrate or sample start, and it shows these analytical properties in measuring amylase activity of sera: no lag phase, detection limit 2.9 U/l, linear range < or = 820 U/l (for 300 s) or < or = 1450 U/l (for 120 s of measurement), and total manual imprecision 3.2% (CV) at 46 U/l. Bilirubin < or = 630 micromol/l, haemoglobin < or =6 g/l, triacylglycerols < or =30 mmol/l, heparin < or =100 kU/l, and glucose < or =120 mmol/l do not interfere. For adults, we established a preliminary 0.95-reference interval of 30-90 U/l not dependent on sex or age. A close association with the IFCC method demonstrates the reliable transfer of its measurement conditions to a robust routine method with minimal changes.