Amylases which produce maltotriose as the major end-product from starc
h are relatively rare. The thermophilic actinomycete, Thermomonospora
fusca, produced an extracellular a-amylase which generated maltotriose
as 61% of the identified products. The addition of maltotriose to a g
lucose-adapted exponential phase culture at 55 degrees C in mineral sa
lts medium caused rapid induction of amylase biosynthesis. Addition of
glucose to cells growing on starch did not repress amylase biosynthes
is because the actinomycete had a marked preference for maltotriose ov
er glucose. The pH and temperature optima for the amylase activity of
concentrated, washed extracellular protein were 6.0 and 65 degrees C,
respectively, with an energy of activation of 59 kJ/mol. The thermosta
bility of the concentrated, washed amylase was increased by the presen
ce of its starch reaction products, but not by added Ca2+.