Studies of the Action Pattern of an α-Amylase from Streptomyces praecox NA-273

抄録

An α-amylase [EC 3. 2. 1. 1] from Streptomyces praecox was purified and its characteristic action, the conversion of maltotriose (G₃) to maltose (G₂) without appreciable formation of glucose (G₁), was investigated. Isoelectric focusing or the glycogen adsorption procedure was employed after chromatography. Isoelectric focusing showed that the enzyme preparation after chromatographic separation comprises three isozymes. The preparation from the glycogen adsorption procedure showed the highest specific activity of any preparation of this enzyme ever obtained. Product analysis with uniformly labeled G₃ revealed that at a high concentration (18mM) of G₃, much more G₂ is produced than G₁ (the product ratio G₂/G₁ is over 20), while at a lower concentration (10 μM) the reaction mixture was composed of nearly equimolar amounts of glucose and maltose. Based on the product analysis of reducing endlabeled G₃ in addition to the above findings, the following conversion mechanism is proposed: Streptomyces α-amylase catalyzes transglycosylation to produce maltotetraose (G₄) as a transient product which is immediately degraded into two molecules of G₂ by a subsequent hydrolytic reaction, i.e., two molecules of G₃ are converted into three molecules of maltose without appreciable formation of glucose.