Properties of maltose-inducible alpha-glucosidase MalL (sucrase-isomaltase-maltase) in Bacillus subtilis: evidence for its contribution to maltodextrin utilization.

Recently, we identified the maltose inducible alpha-glucosidase MalL of Bacillus subtilis. The malL gene encodes a 561-residue protein with amino acid identities to several alpha-glucosidases and is located in a nine-gene spanning gene cluster, which is presumably organized in an operon. MalL was overproduced, purified, and its enzymatic characteristics were described in more detail. This characterization of the enzyme showed a protein stable up to 37 degrees C after temperature treatment for 15 min and exhibiting an optimal reaction temperature of 42 degrees C. Various disaccharides such as sucrose, maltose, and isomaltose were hydrolyzed with different efficiencies. MalL also hydrolyzes longer maltodextrins from maltotriose up to maltohexaose, but not maltoheptaose, palatinose, isomaltotriose, or isomaltotetraose. MalL expression is subject to both maltose induction and carbon catabolite repression. In this article, we present data demonstrating that induction of MalL expression also occurs when starch, amylose, or glycogen are present in the growth medium. The hydrolysis of these substrates by alpha-amylase presumably leads to products which, when taken up into the cytoplasm, trigger the initiation of maltose operon transcription. Furthermore, MalL expression varies temporally, showing a second induction in the stationary growth phase.