A　novel　continuous　spectrophotometric　assay　to　measure　the　activity　of　the　debranching　enzyme　and　alpha-amylase　has　been　developed.　The　assay　mixture　comprises　the　debranching　enzyme　(GlgX　from　Escherichia　coli)　or　alpha-amylase　(PPA　from　porcine　pancreas),　a　reducing　end-specific　alpha-glucosidase　(MalZ),　maltodextrin-branched　beta-cyclodextrin　(Glc(n)-beta-CD)　as　the　substrate,　and　the　glucose　oxidase/peroxidase　system　(GOPOD).　Due　to　its　high　reducing　end　specificity,　the　branch　chains　of　the　substrates　are　not　hydrolyzed　by　MalZ.　After　hydrolysis　by　GlgX　or　PPA,　the　released　maltodextrins　are　immediately　hydrolyzed　into　glucose　from　the　reducing　end　by　MalZ,　whose　concentration　is　continuously　measured　by　GOPOD　at　510　nm　in　a　thermostat　spectrophotometer.　The　kinetic　constants　determined　for　GlgX　(K-m　=　0.66　+/-　0.02　mM　and　k(cat)　=　76.7　+/-　1.5　s(-1))　are　within　a　reasonable　range　compared　with　those　measured　using　high-performance　anion-exchange　chromatography　(HPAEC).　The　assay　procedure　is　convenient　and　sensitive,　and　it　requires　lower　concentrations　of　enzymes　and　substrate　compared　with　dinitrosalicylic　acid　(DNS)　and　HPAEC　analysis.　(C)　2015　Elsevier　Inc.　All　rights　reserved.