Isolation, purification, and characterization of a maltotetraose-producing amylase from Pseudomonas stutzeri

In vivo expression of the Pseudomonas stutzeri maltotetraose-forming amylase gene (amyP)

Northern hybridization and S1 nuclease mapping revealed that the amyP gene coding for maltotetraose-forming amylase of Pseudomonas stutzeri MO-19 is transcribed as a monocistronic mRNA of 2.0 kilobases and that the transcription start site is located 81 base pairs upstream from the first nucleotide of the initiation codon. The amyP gene was expressed weakly in Escherichia coli, and transcription started 49 base pairs downstream of the P. stutzeri MO-19 transcription start site. Synthesis of the amylase in P. stutzeri MO-19 was induced by the addition of maltose to the culture medium and was repressed by the addition of glucose. The induction by maltose was shown to be result of transcription induction of the amyP gene. In contrast, glucose did not repress transcription initiation of amyP, indicating that it controls synthesis of the enzyme, probably at the posttranscriptional level.

Identification and DNA sequencing of a new plasmid (pPST1) in Pseudomonas stutzeri MO-19

A cryptic plasmid, pPST1, was isolated from Pseudomonas stutzeri MO-19 and its complete nucleotide sequence was determined. This plasmid consisted of 1446 bp and could encode a putative polypeptide of 152 amino acid residues (ORF1) in an open reading frame. The putative protein contained a sequence homologous to the sequences found in DNA-binding sites.

Nucleotide sequence of the maltotetraohydrolase gene from Pseudomonas saccharophila

The nucleotide sequence of the Pseudomonas saccharophila gene encoding maltotetraohydrolase (G4-forming amylase) has been determined. The coding region for the G4-forming amylase precursor contained 1653 nucleotides. The deduced precursor protein included an N-terminal 21-residue putative signal peptide; the deduced mature form of G4-forming amylase contains 530 amino acid residues with a calculated molecular mass of 57 740 Da. Sequence similarities between the G4-forming amylase and other amylolytic enzymes of species ranging from prokaryotes to eukaryotes are quite limited. However, three regions, which are involved in both the catalytic and substrate-binding sites of various amylolytic enzymes, are highly conserved in the G4-forming amylase of P. saccharophila.

Detection of a covalent intermediate in the mechanism of action of porcine pancreatic alpha-amylase by using 13C nuclear magnetic resonance

The catalytic mechanism of porcine pancreatic alpha-amylase (1,4-alpha-D-glucan glucanohydrolase, EC 3.2.1.1) has been examined by nuclear magnetic resonance (NMR) at subzero temperatures by using [1-13C]maltotetraose as substrate. Spectral summation and difference techniques revealed a broad resonance peak, whose chemical shift, relative signal intensity and time-course appearance corresponded to a beta-carboxyl-acetal ester covalent enzyme-glycosyl intermediate. This evidence supports a double-displacement covalent mechanism for porcine pancreatic alpha-amylase-catalyzed hydrolysis of glycosidic linkages, based on the presence of catalytic aspartic acid residues within the active site of this enzyme.

Cloning and nucleotide sequence of the gene (amyP) for maltotetraose-forming amylase from Pseudomonas stutzeri MO-19

The gene (amyP) coding for maltotetraose-forming amylase (exo-maltotetraohydrolase) of Pseudomonas stutzeri MO-19 was cloned. Its nucleotide sequence contained an open reading frame coding for a precursor (547 amino acid residues) of secreted amylase. The precursor had a signal peptide of 21 amino acid residues at its amino terminus. An extract of Escherichia coli carrying the cloned amyP had amylolytic activity with the same mode of action as the extracellular exo-maltotetraohydrolase obtained from P. stutzeri MO-19. A region in the primary structure of this amylase showed homology with those of other amylases of both procaryotic and eucaryotic origins. The minimum 5' noncoding region necessary for the expression of amyP in E. coli was determined, and the sequence of this region was compared with those of Pseudomonas promoters.

Microbial amylolytic enzymes

Starch-degrading, amylolytic enzymes are widely distributed among microbes. Several activities are required to hydrolyze starch to its glucose units. These enzymes include alpha-amylase, beta-amylase, glucoamylase, alpha-glucosidase, pullulan-degrading enzymes, exoacting enzymes yielding alpha-type endproducts, and cyclodextrin glycosyltransferase. Properties of these enzymes vary and are somewhat linked to the environmental circumstances of the producing organisms. Features of the enzymes, their action patterns, physicochemical properties, occurrence, genetics, and results obtained from cloning of the genes are described. Among all the amylolytic enzymes, the genetics of alpha-amylase in Bacillus subtilis are best known. Alpha-Amylase production in B. subtilis is regulated by several genetic elements, many of which have synergistic effects. Genes encoding enzymes from all the amylolytic enzyme groups dealt with here have been cloned, and the sequences have been found to contain some highly conserved regions thought to be essential for their action and/or structure. Glucoamylase appears usually in several forms, which seem to be the results of a variety of mechanisms, including heterogeneous glycosylation, limited proteolysis, multiple modes of mRNA splicing, and the presence of several structural genes.

Starch metabolism in Pseudomonas stutzeri. II. Purification and properties of a dextrin glycosyl-transferase (D-enzyme) and amylomaltase

Amylomaltase and disproportionating enzyme (D-enzyme) were purified to homogeneity from cell-free extracts of Pseudomonas stutzeri using a six-step procedure. The presence of both glycosyltransferases in the same organism has not been reported before. Molecular weight determination by gel chromatography gave a value of 74,000 for the amylomaltase and 115 000 for the D-enzyme. Two subunits of different molecular weight were found in each enzyme as proved by sodium dodecyl sulfate-gel electrophoresis. The optimum pH of amylomaltase and D-enzyme activity is 7.6--7.7. Action of both glycosyltransferases on different maltodextrins showed that amylomaltase is most active with maltotetraose, and the Km value for this substrate is 7.1 mM. D-Enzyme catalyzed glucose release from maltose (Km = 8.3 mM) at a higher rate than from maltotriose and maltotetraose. With maltotriose as initial substrate, D-enzyme forms glucose, maltopentaose, maltoheptaose, maltononaose, maltoundecaose as major products. Amylomaltase acts on maltotriose, maltotetraose, and maltopentaose to form a series of homologous 1,4-alpha-glucans. No essential chain-lengthening reaction occurred with maltohexaose.

Starch metabolism in Pseudomonas stutzeri. I. Studies on maltotetraose-forming amylase

The extracellular maltotetraose-forming amylase of Pseudomonas stutzeri was purified to homogeneity by a combination of affinity and hydroxyapatite chromatography. Sodium dodecyl sulfate-gel electrophoresis indicated that the oligomeric enzyme contains two different subunits with molecular weights of 48 000 and 58 000. Cross-linking studies using dimethyl suberimidate have demonstrated that the native enzyme consists of dimers. Seven isozymes of the amylase have been identified after polyacrylamide gel electrophoresis and amylose-digestion zymograms. The amylase of Ps. stutzeri is known to produce maltotetraose from linear and branched alpha-glucans by an exomechanism. The relatively high conversion rate of starch (75% hydrolysis), and the hydrolysis of cross-linked blue starch by this amylase indicate that the enzyme can cleave its substrates also by an endomechanism. Further strong evidence for an endomechanism was obtained from the action of the amylase on maltotetraose units which are located within the pullulan molecule. Dextran, pullulan, and maltotetraose are compeititve inhibitors. EDTA caused reversible inactivation. Amylase activity could be restored by addition of Ca2+. Heavy metals are inhibitory.

The influence of chain size and molecular weight on the kinetic constants for the span glucose to polysaccharide for rabbit muscle glycogen synthase

The kinetic constants for the series of glucosyl acceptors for homogeneous rabbit muscle glycogen synthase I form free of glycogen were examined. The acceptors included glucose, maltose, G3, G4, G6, two hydrolyzed amyloses, amylodextrin and seven polysaccharides including amylopectin and glycogen. S0.5 and relative Vmax were estimated in each case. From these data a two site model of the enzyme is proposed, composed of a polysaccharide binding site and a separate catalytic site, the latter composed of several subsites.

Purification and some properties of a novel maltohexaose-producing exo-amylase from Aerobacter aerogenes

Maltohexaose producing amylase (EC 3.2.1.-) is the fourth known exo-amylase, the three previously known being glucoamylase, beta-amylase and Pseudomonas stutzeri maltotetraose producing amylase. The enzyme after release from Aerobacter aerogenes cells by 0.1% sodium lauryl sulfate extraction was purified by ammonium sulfate precipitation, DEAE-Sephadex column chromatography and Sephadex G-100 gel filtration to 80-fold of the original sodium lauryl sulfate extract activity, It gave a single band on disc electrophoresis, and the molecular weight by gel filtration was 54 000. This amylase showed maximal activity at 50 degrees C and pH 6.80. The pH stability range was relatively wide, the enzyme retaining more than 90% of its initial activity in the range of 6.50-9.0. 80% of the activity was retained after 15 min at 50 degrees C. This enzyme produced maltohexaose from starch, amylose and amylopectin by exo-attack, but did not act on alpha- or beta-cyclodextrin, pullulan or maltohexaitol. Also the enzyme acted on beta-limit dextrins of amylopectin and glycogen to form branched oligosaccharides. The unusual reaction of this enzyme on beta-limit dextrin is discussed from the standpoint of the stereochemistry of 1,4-alpha- and 1,6-alpha-glucosidic bonds. This is the anomalous amylase for which it is recognized that 1,6-alpha-glucosidic linkages in the substrates can mimic the effect of 1,4-alpha-bonds, as previously observed in pseudo-priming reactions of E. coli phosphorylase.

Extracellular alkaline amylase from a Bacillus species

A selective medium was used to isolate a bacterium (Bacillus species NRRL B-3881) that produced extracellular alkaline amylase in an alkaline medium (pH 9.5). Maximal enzyme yield was obtained in an aerated medium after 21 hr at 36 C. The enzyme was purified 18-fold by ultrafiltration and ammonium sulfate precipitation. Three active isoenzymes (one major and two minor) of alkaline amylase were detected by disc electrophoresis in polyacrylamide gel. The enzyme was only 12% inactivated by 20 mm ethylenediaminetetraacetic acid after 1 hr at pH 9.2 and 32 C. The optimal temperature was 50 C at pH 9.2, and the optimal pH was 9.2 at 50 C. The enzyme was stable between pH 7.5 and 10. It had an endomechanism of substrate encounter. The products produced from amylose and amylopectin had the beta-configuration. Cyclomaltoheptaose was hydrolyzed to maltotriose, maltose, and glucose. The main final product produced from amylose and amylopectin was beta-maltose; the other final products were maltotriose and small quantities of glucose and maltotetraose. The predominant product at early stages of hydrolysis was maltotetraose; other products were maltose through maltonanaose.