Action pattern of human pancreatic alpha-amylase on maltoheptaose, a substrate for determining alpha-amylase in serum

The mechanism of action of alpha-amylase from Lactobacillus fermentum on maltooligosaccharides

The action pattern of Lactobacillus fermentum alpha-amylase (FERMENTA) was examined using a series of maltooligosaccharides (G2-G7) as substrates. Structurally, this enzyme has a molecular mass (106 kDa) almost twofold higher than alpha-amylases from mammalians and cereals. The product pattern was investigated through an analysis of products and substrates using HPAEC with pulsed amperometric detection. FERMENTA was consistent with an endo-type of amylase. The bond cleavage frequencies were studied using maltooligosaccharides of various chain lengths as substrate, i.e. maltose up to maltoheptaose and DP 4900-amylose catalyzed by FERMENTA. The catalytic efficiency (k(cat)/K(m)) increased with chain length from maltose (8.7 x 10(4) M(-1) s(-1)) up to amylose (1 x10(9) M(-1) s(-1)). These action pattern results revealed that FERMENTA can readily cleave the third linkage from the reducing end of the maltooligosaccharides (G5-G7).

Subsite mapping of human salivary alpha-amylase and the mutant Y151M

This study characterizes the substrate-binding sites of human salivary alpha-amylase (HSA) and its Y151M mutant. It describes the first subsite maps, namely, the number of subsites, the position of cleavage sites and apparent subsite energies. The product pattern and cleavage frequencies were determined by high-performance liquid chromatography, utilizing a homologous series of chromophore-substituted maltooligosaccharides of degree of polymerization 3-10 as model substrates. The binding region of HSA is composed of four glycone and three aglycone-binding sites, while that of Tyr151Met is composed of four glycone and two aglycone-binding sites. The subsite maps show that Y151M has strikingly decreased binding energy at subsite (+2), where the mutation has occurred (-2.6 kJ/mol), compared to the binding energy at subsite (+2) of HSA (-12.0 kJ/mol).

Subsite mapping of the binding region of alpha-amylases with a computer program

A computer program has been evaluated for subsite map calculations of depolymerases. The program runs in windows and uses the experimentally determined bond cleavage frequencies (BCFs) for determination of the number of subsites, the position of the catalytic site and for calculation of subsite binding energies. The apparent free energy values were optimized by minimization of the differences of the measured and calculated BCF data. The program called suma (SUbsite Mapping of alpha-Amylases) is freely available for research and educational purposes via the Internet (E-mail: gyemant@tigris.klte.hu). The advantages of this program are demonstrated through alpha-amylases of different origin, e.g. porcine pancreatic alpha-amylase (PPA) studied in our laboratory, in addition to barley and rice alpha-amylases published in the literature. Results confirm the popular 'five subsite model' for PPA with three glycone and two aglycone binding sites. Calculations for barley alpha-amylase justify the '6 + 2 + (1) model' prediction. The binding area of barley alpha-amylase is composed of six glycone, two aglycone binding sites followed by a barrier subsite at the reducing end of the binding site. Calculations for rice alpha-amylase represent an entirely new map with a '(1) + 2 + 5 model', where '(1)' is a barrier subsite at the nonreducing end of the binding site and there are two glycone and five aglycone binding sites. The rice model may be reminiscent of the action of the bacterial maltogenic amylase, that is, suggesting an exo-mechanism for this enzyme.

Examination of the active sites of human salivary alpha-amylase (HSA)

The action pattern of human salivary amylase (HSA) was examined by utilising as model substrates 2-chloro-4-nitrophenyl (CNP) beta-glycosides of maltooligosaccharides of dp 4-8 and some 4-nitrophenyl (NP) derivatives modified at the nonreducing end with a 4,6-O-benzylidene (Bnl) group. The product pattern and cleavage frequency were investigated by product analysis using HPLC. The results revealed that the binding region in HSA is longer than five subsites usually considered in the literature and suggested the presence of at least six subsites; four glycone binding sites (-4, -3, -2, -1) and two aglycone binding sites (+1, +2). In the ideal arrangement, the six subsites are filled by a glucosyl unit and the release of maltotetraose (G4) from the nonreducing end is dominant. The benzylidene group was also recognisable by subsites (-3) and (-4). The binding modes of the benzylidene derivatives indicated a favourable interaction between the Bnl group and subsite (-3) and an unfavourable one with subsite (-4). Thus, subsite (-4) must be more hydrophylic than hydrophobic. As compared with the action of porcine pancreatic alpha-amylase (PPA) on the same substrates, the results showed differences in the three-dimensional structure of active sites of HSA and PPA.

Synthesis of chromogenic substrates of alpha-amylases on a cyclodextrin basis

One-pot acetylation and subsequent partial acetolysis of alpha-, beta- and gamma-cyclodextrins resulted in crystalline peracetylated malto-hexaose, -heptaose, and -octaose, respectively. Prolonged acetolysis of beta-cyclodextrin gave a mixture of acetylated maltooligosaccharides, from which peracetylated malto-triose, -tetraose, and -pentaose were isolated. The acetylated oligosaccharides were converted into alpha-acetobromo derivatives, and then transformed into 4-nitrophenyl and 2-chloro-4-nitrophenyl beta-glycosides. From the 4-nitrophenyl glycosides 4,6-O-benzylidene derivatives were prepared, which were used together with the free glycosides as substrates of porcine pancreatic alpha-amylase.

Action pattern of porcine pancreatic alpha-amylase on three different series of beta-maltooligosaccharide glycosides

A technique for the investigation of the action pattern of porcine pancreatic amylase (PPA) has been developed by utilising as model substrates 2-chloro-4-nitrophenyl (CNP) and 4-nitrophenyl (NP) beta-glycosides of maltooligosaccharides of dp 4-8 and some NP derivatives modified at the nonreducing end with a 4,6-O-benzylidene (Bnl) group. The action pattern was investigated by the method of product analysis, using an HPLC method. The product pattern and cleavage frequency was very similar in the CNP- and NP-oligomers and showed that the glucopyranose residue could be replaced by the aglycon group. Modification of the nonreducing end of NP glycosides to give a 4,6-O-benzylidene-D-glucopyranosyl group indicated a favourable interaction between the Bnl group and the subsites (-3) and (-5) but an unfavourable one with subsite (-4), which resulted in a clear shift in the product pattern. The results obtained with the digestion of the benzylidene-protected substrates confirm a multiple attack mechanism for PPA.

Determination of enzyme activity by high-performance liquid chromatography

The application of high-performance liquid chromatography (HPLC) in the study of enzymatic reactions is reviewed. The rationale for using HPLC is given and whether the components of the reaction mixture should be derivatized prior to or after HPLC. An alphabetical list of enzymes assayed by HPLC is given. Substrate and product are included as well the derivatization reagent, detection method and biological matrix. Specific examples of these assays in a complex biological matrix viz. faeces are given. Future prospects are the detection of new enzymes using synthetic substrates and implementation of mass spectrometry to elucidate enzyme specificities.

Effects of cholecystokinin-receptor blockade on pancreatic and biliary function in healthy volunteers

This study used the specific cholecystokinin (CCK)-receptor antagonist loxiglumide to evaluate whether endogenous CCK, which is released after a meal, regulates pancreatic and biliary functions. Eight healthy volunteers were studied twice on separate days. The subjects received a continuous intraduodenal infusion of a 750-kcal liquid test meal for 2 hours either with or without IV infusion of 5 mg.kg-1.h-1 of loxiglumide. Loxiglumide at this dose abolishes the actions of CCK at various target organs including gallbladder and pancreas, when given at doses that mimic postprandial plasma concentrations of CCK. Loxiglumide markedly decreased the meal-stimulated outputs of amylase, trypsin, and chymotrypsin by 55%-70% of control values but only slightly decreased duodenal volume (25% inhibition of mean integrated secretion). Loxiglumide abolished gallbladder emptying induced by infusion of nutrients and even increased gallbladder volumes when compared with prior fasting values. Correspondingly, loxiglumide almost abolished the output of bilirubin after infusion of nutrients. However, loxiglumide failed to alter the increase in circulating concentrations of glucose, insulin, and C peptide after infusion of nutrients. The present results show that CCK is one of several factors that regulate pancreatic protein secretion after absorption of nutrients. However, CCK is probably not involved in regulation of pancreatic secretion of fluid. In contrast, gallbladder function is mainly regulated by CCK, both in terms of its emptying after intestinal absorption of nutrients and in terms of maintenance of its fasting volume. Cholecystokinin does not play a major physiological role as an insulinotropic factor.

Released prophospholipase A2 activation peptides in the rapid early prediction of trauma outcome: a preliminary report

Clinical scores of trauma severity may not be adequate measures of trauma-related systemic pathophysiology to be useful in the early prediction of individual patient outcome. This preliminary study evaluates the role of Prophospholipase A2 Activation Peptide (PLAP), measured in patient urine by modified enzyme-linked immunosorbent assay (ELISA), as an early prognostic in the severely injured. Of nine polytrauma patients requiring intensive care after a major accident, two died and one was permanently severely disabled (group 1), whilst six made a full recovery (group 2). These two groups had different ranges of urine PLAP concentration (P = 0.024). Phospholipase A2 (PLA2) activation may be an early event in tissue damage pathways that lead to multisystem organ failure (MSOF). We believe urine and plasma PLAP concentrations merit further evaluation for the early prediction of individual trauma outcome.

Effects of intravenous infusion of amino acids, fat, or glucose on unstimulated pancreatic secretion in healthy humans

The effects of intravenous infusion of amino acids, fat, or glucose on unstimulated pancreatic secretion were studied in 31 healthy male volunteers. Each subject was studied twice on two separate days. On both days pancreatic outputs were measured during a 4-hr basal period that was followed by a 4-hr test period. During the test period either one of the digestive end products (100 ml/hr 10% amino acids in 13 subjects; 100 ml/hr 10% fat in 8 subjects; 150 ml/hr 10% glucose in 10 subjects) or saline was intravenously infused. The infusion of the digestive end products or saline on the two separate days was done in a randomized order. Six of the 10 subjects that had already been studied for glucose received a higher glucose dose (100 ml 20% glucose as a bolus followed by 300 ml/hr 10% glucose) in a third additional experiment. Intravenous infusion of amino acids significantly stimulated pancreatic outputs of trypsin and chymotrypsin, but left the outputs of amylase, lipase, bicarbonate, and volume unaffected. The low-glucose dose, as well as the fat infusion did not alter any of the pancreatic outputs. To analyze the relationships between different enzymes during the infusion of digestive end products, regression lines were calculated from the scatter of all individual pairs of enzyme measurements. Significantly different regression functions found for each condition (NaCl control, amino acids, fat, glucose) when trypsin and chymotrypsin were plotted versus lipase and amylase: amino acids shifted the function to a trypsin- and chymotrypsin-dominant pattern of secretion, glucose to an amylase-dominant pattern, and fat to a lipase-dominant pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of verapamil on exocrine pancreatic secretion in man

Calcium ions are thought to mediate hormonal and cholinergic stimulation of exocrine pancreatic secretion. In order to further eludicate the role of calcium ions in stimulus-secretion coupling of the pancreas, the effect of the calcium antagonist verapamil, which inhibits transmembrane calcium influx, was studied on pancreatic secretion in 35 healthy male volunteers. Every subject had two stimulation periods of 2 hr each with a 3-hr period between the two. Pancreatic secretion was stimulated by cholecystokinin in 12 subjects, by secretin in 14 subjects, and by sham feeding in 6 subjects. Three subjects were studied without any secretory stimulus. Verapamil as an intravenous bolus of 150 micrograms/kg followed by an intravenous infusion of 150 micrograms/kg/hr or saline were given during the two 2-hr stimulation periods in a randomized order. The pancreatic secretory responses to stimulation by cholecystokinin, secretin, or sham feeding, as well as the basal pancreatic secretion without a secretory stimulus were left unaffected by verapamil when compared to the saline control. The results, therefore, call into question the hypothesis that transmembrane calcium influx is a major mediator of pancreatic secretion in response to hormonal or cholinergic stimulation in man.

Action pattern of serum amylase using p-nitrophenyl-maltoheptaoside as substrate

Selected serum samples with different isoamylase patterns, as revealed by agarose gel electrophoresis, were analysed by the Phadebas amylase test, and by using p-nitrophenyl-maltoheptaoside as the substrate. The products with the latter substrate were examined by high performance liquid chromatography (HPLC). For some samples, different catalytic activities were registered by the two amylase methods. In these cases, electrophoresis showed a double pancreatic band associated with increased pancreatic amylase catalytic activity, or an abnormal, broad salivary band associated with increased salivary enzyme catalytic activity. The stoichiometric factors for most of these samples, calculated from the amount of p-nitrophenol detected after HPLC, differed from the mean values.

Evaluation of alpha-amylase assays with 4-nitrophenyl-alpha-oligosaccharides as substrates

Measurements of alpha-amylase with 4-nitrophenyl glucosides offer the following advantages over methods that rely on the formation of NADH: a short lag phase, no apparent interference by metabolites and enzymes of the sample and extremely stable substrates with low blank values. The intrinsic sensitivity of nitrophenol formation was equal to that of hydrolysis of maltotetraose, but was less than that of glucose-producing methods using oligosaccharides. In contrast to starch, the chromogenic substrates are more rapidly hydrolysed by salivary than by pancreatic amylase. Disadvantages of these substrates are: higher turnover by animal than by human amylases, and a marked susceptibility of the chromophore to small changes of pH and protein concentration. Some analytical qualities such as specificity, accuracy, precision, stability of the substrate and linear range are described in detail and compared with those of other methods.