Glucose Forming Enzyme from Sulfolobus shibatae
Isabella DI LERNIAa, Alessandra MORANAa, Mose ROSSI*b, Mario DE ROSAa
a Istituto di Biochimica delle Macromolecole, Consiglio Nazionale delle Ricerche
b Istituto di Biochimica delle Proteine ed Enzimologia, Consiglio Nazionale delle Ricerche, Via Marconi, 10, 80125-Napoli, Italy
Different strains of Sulfolobales are able to form glucose from starch and dextrines (1). The amylolytic activity was found in the cell free extract and in the cell membrane of the hyperthermophilic acidophilic archaeon S. shibatae. The S. shibatae enzyme, starting from the non reducing end of the polysaccharide chain, catalyzed, in a stepwise manner, the hydrolysis of theα-1,4 linkages. The enzyme shows an optimum of temperature and pH at 85℃ and 5.5, respectively; the molecular weigth is about 200 kDa and pI is about 5.0. The enzyme maintains 100% of activity when incubated at 75℃ for 24 hs in absence of substrate and its thermostability strongly increases in presence of substrates. These properties and the absence of severe glucose inhibition make this enzyme of industrial interest since thermostable and thermophilic enzymes could be used in the saccharification of dextrines for improving the production of glucose from starch. The manufacture of sugars from starch is a multistage process which involves different microbial enzymes in successive steps (2). In the first step starch is liquefied at 105℃ for 5 min and later at 95℃ for 90 min by a thermostable α-amylase at pH 5.0-6.0. For the saccharification of dextrines in the second step usually a glucoamylase from Aspergillus niger is used. Due to differences between the two utilized enzymes, all conditions of this second step have to be varied, lowering the temperature and pH to 60℃ and 4.5, respectively. The variation of different parameters in the above-mentioned multistage process increases the industrial production cost. The use of S. shibatae glucoamylase in the saccharification step would therefore improve the starch conversion process; the enzyme, working in the same reaction conditions of the liquefaction step, would significantly lower the cost of sugar syrup production.
1. Lama, L., Nicolaus, B., Trincone, A., Morzillo, P., De Rosa, M., and Gambacotta, A. (1990) Biotech. Lett., 12, 431-432.
2. Coker, L. E., et al. (1985) in Comprehensive Biotechnology, Pergamon Press, Oxford, 3, 777.
