Enzymatic Characterisation of Novamyl®, a Thermostable α-Amylase

The thermostable -amylase Novamyl® is used in the baking industry as an antistaling agent due to its ability to reduce retrogradation of amylopectin. We have studied its enzymatic properties at pH 5.0. We make two main conclusions: (1) Novamyl® shows sequence homology to cycloglycosyl transferases (CGTases); like these enzymes, Novamyl® cleaves cyclodextrins, forms transglycosylation products and is subject to product inhibition by maltose. Novamyl® has 5 subsites in the active site and is also subject to substrate inhibition. (2) Novamyl® is clearly different from exoglucanases like β-amylase and glucoamylase. It is able to hydrolyse a pentasaccharide with bulky substituents at both ends (INdp5) and is inhibited by the α-amylase inhibitor Trestatin A. Although Novamyl® appears unable to hydrolyse α-1,6-linkages, it is able to degrade amylopectin to a greater extent than β-amylase as well as β-limit dextrins. Novamyl® degrades amylose in such a manner that initially the molecular weight is drastically reduced while β-amylase does not show any detectable effect on the molecular weight of this substrate. Products of the degradation of amylopectin and amylose by Novamyl® are maltose and oligosaccharides, whereas β-amylase and glucoamylase produce only maltose and glucose, respectively. This was shown in baking experiments as well. The new data presented here clearly show that unlike exoamylases, Novamyl® does not require a non-reducing end and attacks amylose, Indp5 and cyclodextrins in an endo-like manner. Based on these results Novamyl® should be reclassified.