Pectinases are a group of enzymes responsible for plant tissue maceration and consist of a number of enzymes that are classified according to their mode of action and the substrates they prefer, viz. pectin esterases (EC 3.1.1.11), polygalacturonases (EC 3.2.1.15), pectate lyases (EC 4.2.2.2), and pectin lyases (PNL) (EC 4.2.2.10). Amongst these, PNL are of particular interest because they degrade pectin polymers directly by the β- elimination mechanism that results in the formation of 4,5-unsaturated oligogalacturonides, while other pectinas- es act sequentially to degrade pectin molecule totally. The major source of PNL on industrial scale is fungi belonging to the genera Aspergillus, Penicillium, and Fusarium, although a few bacterial PNL are also reported [1]. Solid- state fermentation (SSF) has emerged as preferred tech- nology in industrial fermentation as it offers several practi- cal and economical advantages [2]. Agro-industrial residues and wastes such as wheat bran, rice bran, sugar- cane bagasse, corncobs, citrus wastes, apple pomace, and a variety of such byproducts are potentially good substrates for SSF [3]. Acidic PNL have biotechnological potential in fruit juice industries due to the fact, that they degrade pectin without disturbing the ester group, which is respon- sible for specific aroma of the juice, and also it does not lead to formation of the toxic alcohol methanol. Though there is a considerable amount of literature on application of acidic PNL in juice clarifying activity [4-6], reports on retting of natural fiber by alkaline PNL are few [7]. Retting is a process of fiber separation from non-fiber parts of plants. The plant fibers are held togeth- er by pectin, and pectin plays an important role as a binder between adjacent cells [8]. Since PNL degrades pectin, it is expected that it should play a role in the ret- ting of natural fibers. Fibers present in the stems of many herbaceous dicots, such as flax (Linum usitatissimum), Indian hemp (Cannabis sativa), and Sunn hemp (Crotalaria juncea) are potent source of fibers for textile industries. This communication reports on the purifica- tion and characterization of pectin lyase secreted by P. citrinum MTCC 8897 and retting of L. usitatissimum, C. sativa, and C. juncea fibers by the purified PNL. ISSN 0006-2979, Biochemistry (Moscow), 2009, Vol. 74, No. 7, pp. 800-806. © Pleiades Publishing, Ltd., 2009. Published in Russian in Biokhimiya, 2009, Vol. 74, No. 7, pp. 985-992. 800 Abbreviations: PNL, pectin lyase; SSF, solid-state fermentation. * To whom correspondence should be addressed. Purification and Characterization of Pectin Lyase Secreted by Penicillium citrinum S. Yadav 1 *, P. K. Yadav 2 , D. Yadav 2,3 , and K. D. S. Yadav 1 1 Department of Chemistry, D. D. U. Gorakhpur University, Gorakhpur 273009, India; E-mail: sangeeta_rahul@rediffmail.com 2 Department of Biotechnology, D. D. U. Gorakhpur University, Gorakhpur 273009, India 3 Department of Molecular Biology and Genetic Engineering, College of Basic Sciences and Humanities, G. B. Pant University of Agriculture and Technology, Pantnagar (Uttarakhand) 263145, India Received August 5, 2008 Revision received October 20, 2008 Abstract—The importance of various parameters such as sugarcane juice concentration, pH of the medium, and effects of different solid supports for maximum secretion of pectin lyase from Penicillium citrinum MTCC 8897 has been studied. The enzyme was purified to homogeneity by Sephadex G-100 and DEAE-cellulose chromatography. The molecular mass deter- mined by SDS-PAGE was 31 kDa. The K m and k cat values were found to be 1 mg/ml and 76 sec –1 , respectively. The opti- mum pH of the purified pectin lyase was 9.0, though it retains activity in the pH 9.0-12.0 range when exposed for 24 h. The optimum temperature was 50°C, and the pectin lyase was found to be completely stable up to 40°C when exposed for 1 h. The purified pectin lyase was found efficient in retting of Linum usitatissimum, Cannabis sativa, and Crotalaria juncea. DOI: 10.1134/S0006297909070141 Key words: pectin lyase, retting, solid state fermentation, Penicillium citrinum, Cannabis sativa, Crotalaria juncea, Linum usi- tatissimum