BIOTECHNOLOGICALLY RELEVANT ENZYMES AND PROTEINS The 53-kDa proteolytic product of precursor starch-hydrolyzing enzyme of Aspergillus niger has Taka-amylase-like activity K. Ravi-Kumar & K. S. Venkatesh & S. Umesh-Kumar Received: 24 July 2006 / Revised: 30 October 2006 / Accepted: 2 November 2006 / Published online: 23 November 2006 # Springer-Verlag 2006 Abstract The 53-kDa amylase secreted by Aspergillus niger due to proteolytic processing of the precursor starch-hydrolyzing enzyme was resistant to acarbose, a potent α-glucosidase inhibitor. The enzyme production was induced when A. niger was grown in starch medium containing the inhibitor. Antibodies against the precursor enzyme cross-reacted with the 54-kDa Taka-amylase protein of A. oryzae. It resembled Taka-amylase in most of its properties and also hydrolyzed starch to maltose of α- anomeric configuration. However, it did not degrade maltotriose formed during the reaction and was not inhibited by zinc ions. Keywords Aspergillus niger . Proteolytic processing . Starch-hydrolyzing enzyme . Acarbose . Taka-amylase . α-anomeric configuration Introduction Amylases (EC 3.2.1.1) or starch-hydrolyzing enzymes have varied industrial applications. In brewing industry, the products of starch obtained after enzymatic hydrolysis are used as nutrients in microbial fermentation (Stewart and Russel 1978) for ethanol production (Ueda et al. 1981; Matsumoto et al. 1982). Acetone, butanol and lactic acid fermentations by microorganisms also use enzyme-hydro- lyzed starch products as substrates (Beech 1953; Mashell 1959). However, food industries constitute the major market for amylases for the preparation of sweeteners and syrups from starch (reviewed by Saha and Zeikus 1989; Nigam and Singh 1995; Ravi-Kumar and Umesh-Kumar 2006). Of the microbial amylases used in the above processes, enzymes characterized from Aspergillus niger find application in industrial glucose production (reviewed by Fogarty and Kelly 1979). Two forms of glucoamylase varying in molecular mass were described from A. niger (Lineback et al. 1969; Svensson et al. 1986). Whereas differential splicing of the mRNA as the cause for the secretion of the two forms of glucoamylase was reported by Boel et al. (1984a,b), some studies hypothesized the 61-kDa enzyme as a post- translational proteolytic product of the 71-kDa protein. Although the identification of the precursor starch-hydro- lyzing enzyme in A. niger culture broths (Suresh et al. 1999) and its in situ proteolytic activity caused the production of the two glucoamylases and a 53-kDa α- amylase (Dubey et al. 2000; Ravi-Kumar et al. 2004), the studies did not characterize the α-amylase. Recently, a Taka-amylase-like activity was identified in this protein, and unlike the other amylases, it was not inhibited by acarbose, an α-glucosidase inhibitor (Salehi et al. 1995). An enhanced production of the enzyme also occurred Appl Microbiol Biotechnol (2007) 74:1011–1015 DOI 10.1007/s00253-006-0742-6 K. Ravi-Kumar (*) : K. S. Venkatesh : S. Umesh-Kumar Department of Food Microbiology, Central Food Technological Research Institute, Mysore 570020, India e-mail: r-kadeppagari@northwestern.edu Present address: K. Ravi-Kumar Department of Microbiology–Immunology, Feinberg School of Medicine, Northwestern University, 303, East Chicago Avenue, Chicago, IL 60611, USA Present address: K. S. Venkatesh Department of Physiology, University of Tennessee Health Science Center, 894, Union Avenue, Memphis, TN 38163, USA