An assay for pullulanase in the presence of other carbohydrases

Cloning of the debranching-enzyme gene from Thermoanaerobium brockii into Escherichia coli and Bacillus subtilis

The gene for an enzyme with single or dual specificity on complex carbohydrates has been transferred from its native host (Thermoanaerobium brockii), a thermophilic anaerobe, into Escherichia coli and Bacillus subtilis. Most of the gene coding region is in a 2.2-kilobase PstI fragment that is common to the E. coli and B. subtilis chimeric vectors pCPC902 and pCPC903, respectively. Although the T. brockii debranching enzyme secreted from B. subtilis was unglycosylated and had less thermostability, more enzyme was secreted from B. subtilis (0.80 to 1.0 U/ml) than from T. brockii (0.23 U/ml). E. coli did not export any measurable enzyme. From the fermentation broth of B. subtilis containing pCPC903, three active species of the debranching enzyme were separated; two species are possibly protease digestion products of the larger protein (105,000 molecular weight). Whereas the enzyme can cleave all of the alpha-1----6 glucosidic linkages (and none of the alpha-1----4 bonds) in pullulan, it hydrolyzed mostly alpha-1----4 and very few of the alpha-1----6 linkages in starch. Upon hydrolysis of pullulan by the enzyme, only maltotriose was produced, while starch was digested to various-sized oligomers.

Detection of pullulanase in polyacrylamide gels using pullulan-reactive red agar plates

After electrophoresis, active pullulanase bands in acrylamide gels have been detected by overlaying and then incubating the gel on a replica gel containing 2.5% pullulan-reactive red conjugate and 2.1% agar. The enzyme activity is revealed as a clear band against a red background on the replica gel. The sensitivity of the replica plate is such that 0.0012 unit of Klebsiella aerogenes pullulanase can be detected easily. This procedure is effective in enzyme screening to distinguish pullulanase from other carbohydrases.