No abstract

No abstract

No abstract

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 . 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.Under appropriate culture conditions, Pseudomonas stutzeri produces an extracellular amylase that forms maltotetraose (EC 3.2.1.60, exo-maltotetraohydrolase; abbreviated as G4-amylase) (21). This enzyme is a unique amylase because it catalyzes the release of a-anomeric oligosaccharide (ot-maltotetraose) exoglycolytically from the nonreducing ends of starch (23), whereas other exo-type amylases (glucoamylase and ,-amylase) release P-anomeric products by exoglycolytic cleavage, and ox-amylases hydrolyze starch endoglycolytically to produce ot-malto-oligosaccharides. Thus, the G4-amylase has unique activity for hydrolysis of starch intermediate between those of (x-amylases and P-or gluco-amylase; G4-amylase produces a similar product to a-amylases but hydrolyzes starch exoglycolytically like P-or gluco-amylase.Robyt and Ackerman (21) reported that the G4-amylase of P. stutzeri consists of isozymes. Multiple forms of this enzyme (seven isozymes) varying in molecular weight and isoelectric point were also reported by Schmidt and John (26). Sakano et al. (23,24) purified two forms of enzyme (F-1 and F-2), each giving a single band on polyacrylamide gel electrophoresis with or without sodium dodecyl sulfate. The enzymatic properties of F-1 and F-2 were the same, but their isoelectric points were different. The reason for the multiple forms of the enzyme is still unknown.G4-amylase is commercially important for producing maltotetraose, which is used as a substrate of amylases in studies on their mode of action and as a highly sensitive substrate for detection of ot-amylase when coupled with a chromogenic compound. Maltotetraose is also being tested for use as a food additive to improve the texture and moisture retention of foods.As an initial step in understanding the molecular basis of the unique action mechanism of G4-amylase and the genetic basis of its multiple forms and also for elucidating the regulation of the synthesis of this industrially important enzyme, we cloned and sequenced the G4-amylase gene (amyP) from P. stutzeri. Then, we compared its amino acid * Corresponding author. sequence with those of other amylases of both procaryotic and eucaryotic origins. MATERIALS AND METHODSBacterial ...

No abstract