Amylases Producing Specific Maltodextrin Products

In 1978, Wako et al49 described an enzyme from Streptomyces griseus that produced primarily maltotriose from the non-reducing ends of starch chains. Amylose 

Halobacterium sp.,57 Halobacterium halobium5S and Micrococcus halobius59 elaborate amylases that require the presence of Na+, K+ and Ca+2 for activity and stability. Relatively high salt concentrations (2M NaCl or 1M KC1) are required in the culture medium for activity. Purified M. halobius amylase requires 0.25 M NaCl or 0.75 M KC1 for maximum activity. 

An a-amylase from a hyperthermophilic archaebacterium, Pyrococcus furiosus, was purified and found to have optimal activity, with substantial thermal stability, at 100°C.60 Unlike other a-amylases, it is not dependent on calcium ions for activity or stability. The enzyme produces G4, G5 and G6 as the primary products and hydrolyzes these products, as well as G3, but at a much reduced rate, characteristic of a-amylase secondary reactions. 

Using molecular biology techniques, Conrad et al.61 produced hybrids of the a-amylases from B. amyloliquefaciens and B. licheniformis. Thirty-three hybrids were formed. They consisted of the entire a-amylase sequence with variable proportions from B. amyloliquefaciens a-amylase and B. licheniformis a-amylase. The hybrid enzymes fell into six groups that retained the extra-thermostability of the licheniformis enzyme. A specific hybrid sequence (residues 34-76) was correlated with the enzymes product specificity for forming and accumulating maltohexaose. Two of the hybrids were less thermostable than either of the parent types, while two others were enzymatically inactive. 

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Thermophilic archaeal a-amylases do not differ superficially from other a-amylases in their molecular size and amino acid composition. They are primarily monomeric enzymes with molecular weights of 40-70 kDa.84,88-90 Some of these amylases produce specific maltodextrin products, which are also summarized in Table 7.1. 

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