69 MALGORZATA P LESZCZYN; SKA 1 , JANUSZ SZCZODRAK 1 *, JERZY ROGALSKI 2 AND JAN FIEDUREK 1 " Department of Industrial Microbiology, Maria Curie-Sklodowska University, Akademicka 19, 20-033 Lublin, Poland # Department of Biochemistry, Maria Curie-Sklodowska University, M. Curie-Sklodowska Square 3, 20-031 Lublin, Poland The basic hydrolysis parameters, i.e. molecular weight of substrate, reaction time, pH, temperature, and enzyme and substrate concentration, were standardized to maximize sugar yield from dextran. Thus, a 74 % conversion of 4 % dextran to sugar syrup was reached in 12 h using 6 dextranase units g -" hydrolysed substrate. The high concentrations of sucrose in the reaction medium did not affect the hydrolysis efficiency nor the activity of Penicillium notatum dextranase. Action patterns of dextranase from P. notatum on dextran were investigated. Analysis of the dextran hydrolysis end products indicated that P. notatum dextranase was a typical endo-enzyme, and isomaltose and isomaltotriose were identified as the primary final products of dextran hydrolysis. Dextran is a collective name given to a large class of exopolysaccharides composed mainly of α-1,6 glucosidic linkages with minor secondary linkages such as α-1,2, α-1,3 and α-1,4. Microbial synthesis of dextrans in damaged cane and beets or other products containing sucrose is an important problem in the sugar and food industry. Dextran is also a structural component of dental plaque which causes the development of dental caries (Sidebotham, 1974 ; Robyt, 1985). To overcome some of the problems associated with the removal of dextran, enzymes that specifically hydrolyse dextrans of various branched structures are employed. Although related enzymes have been found in mammalian tissues (Preobrazhenskaya, Minakova & Rosenfeld, 1974) and in the coleoptiles of Avena (Heyn, 1981), the richest sources of extracellular dextranases (α-1,6--glucan-6-glucano- hydrolases, EC 3\2\1\11) are mainly microorganisms among which fungi are the most important producers (Miles, 1983). Dextranase can be useful in commercial production of clinical dextran, in studies concerning dextran structure, in obtaining isomaltose and higher isomaltooligomers as well as in preventing the formation of dental caries (Saito, 1982 ; Okada, Sumitomo & Hirasawa, 1986 ; Kim & Day, 1994). The enzymic hydrolysis plays an important role in removing dextran from infected diffusive juices (Stoppok & Buchholz, 1994). Recently it was also found that the dextran- depolymerising enzyme is able to increase the antibiotic efficacy in streptococcal endocarditis (Mghir et al., 1994). In the enzymic hydrolysis of dextran it is essential to obtain a high sugar yield per enzyme unit. Many factors affect this yield, including inhibition of enzyme action by heat or the degradation products, enzyme and substrate concentration, * Corresponding author. molecular weight of substrate, speed of enzyme action, and degree of agitation. In sugar refining, on the other hand, high concentration of sucrose in juices can also affect the efficiency of dextran hydrolysis. Thus, optimization of hydrolysis conditions plays a significant role in the economy of the saccharification process. As for the enzymic hydrolysis of natural dextrans, there have been several papers dealing with the action patterns of some exo- and endodextranases (Tsuru, Hiraoka & Fukumoto, 1972 ; Sugiura & Ito, 1974 ; Wheatley & Moo-Young, 1977). Dextranases from different sources exhibit diverse action patterns, but fundamentally they hydrolyse dextran to isomaltose. Some dextranases gave also -glucose as a final product (Whiting, Sutcliffe & Russell, 1993). In a previous study, a strain of Penicillium notatum was selected as a new effective source of extracellular dextranase, and methods most suitable for obtaining an active dextrano- lytic preparation were evaluated (Pleszczyn! ska, Szczodrak, Fiedurek, 1994 ; Szczodrak, Pleszczyn! ska & Fiedurek, 1994). The purpose of these investigations is to find the best operating conditions for the efficient hydrolysis of dextran by a dextranase from P. notatum, and to identify the final hydrolysis products. MATERIALS AND METHODS Substrates and chemicals Commercial dextrans (average mol. wt : 40, 110 & 500 kDa) were supplied by Polfa Pharmaceutical Works (Kutno, Poland) ; dextran 5–40 MDa (industrial grade), glucose, maltose, isomaltose, isomaltotriose, isomaltotetraose, and p-anisal- dehyde by Sigma Chemical Co. (St Louis, MO, U.S.A.). 3,5- Dinitrosalicylic acid (DNS) was from BDH (Poole, U.K.). All Mycol. Res. 101 (1) : 69–72 (1997) Printed in Great Britain Hydrolysis of dextran by Penicillium notatum dextranase and identification of final digestion products