Chemistry: molecular biology and microbiology – Enzyme – proenzyme; compositions thereof; process for... – Hydrolase
Patent
1994-11-22
1997-08-26
Wax, Robert A.
Chemistry: molecular biology and microbiology
Enzyme , proenzyme; compositions thereof; process for...
Hydrolase
4352567, 435278, C12N 942, C12N 114, D21C 300
Patent
active
056610211
DESCRIPTION:
BRIEF SUMMARY
This application has been filed under 35 U.S.C. .sctn.371 as the national stage application of PCT/FI93/00219, filed May 24, 1993, which claims priority from application Ser. No. 922373, filed May 22, 1992, and application Ser. No. 931193, filed Mar. 17, 1993, both of Finland.
The present invention relates to a DNA sequence which codes for mannanase enzymes. The invention also concerns vectors, yeast and fungus strains containing said DNA sequence. Furthermore the invention relates to a method for isolating genes coding for mannanases and to a method for constructing yeast strains capable of expressing mannanase. The invention also provides an enzyme product containing at least one mannanase and a method for preparing mannanase enzymes and enzyme products. Finally, the invention concerns a process for hydrolyzing mannopolymers and to a process for bleaching lignocellulosic pulps.
The main components of wood are cellulose, lignin and hemicellulose. Softwood mainly comprises arabino-4-O-methylglucuronoxylan, whereas hardwood xylan consists of O-acetyl-4-O-methylglucuronoxylan. The glucomannan polymers are formed by a main chain consisting of glucose and mannanose units. The main chain is substituted with galactose and acetylunits. There are only small mounts (2-5%) of glucomannanes in hardwood and the glucomannan of hardwood trees differs structurally from that of softwood trees in the sense that it is not acetylated nor does it contain galactose side groups (Timell 1967). During chemical pulping the relative mounts of hemicelluloses is changed compared to that of the native tree. The main hemicellulose component of both softwood and hardwood kraft pulp is xylan (Sjostrom 1977). Softwood pulp contains also large mounts of glucomannan. During pulping, a pan of the hemicellulose of the wood is dissolved because of the very alkaline cooking liquor. When the cooking is continued, pH decreases and xylan with no or few side chains will start to precipitate on the surface of the cellulose fibers (Yllner and Enstrom 1956, Yllner et al. 1957). This xylan reprecipitation takes place simultaneously with the precipitation of dissolved lignin. The glucomannan behaves in alkaline cooking conditions in a different way compared to xylan. Softwood glucomannanes are subjected to a partial decomposition already at approx. 130.degree. C. and, thus, the relative proportion of glucomannan in pulp is smaller than in the original softwood (Sjostrom 1977). The glucomannan remaining in the fiber is, howvever, very stable (Simonson 1971). Glukomannan is believed to be evenly distributed within the fiber, wheras the xylan concentration is largest on the surface of the fiber (Luce 1964).
After chemical pulping, the pulp will contain darkened residual lignin which is removed by bleaching. In conventional chlorine bleaching the lignin is dissolved using chlorine or chlorine dioxide. Nowadays oxygen bleaching, hydrogen peroxide and combinations of these and the former are also often used.
It has been found out that the bleachability of the fibres can be improved by using hemicellulases, in particular xylanase, (Kantelinen et al 1988, Viikari et al 1991a). The mounts of enzymes needed for achieving bleaching are small and an enzymatic treatment can easily be combined with pulping processes. In the present applications, thus far enhanced bleachability of the fibres has been achieved by hydrolyzing the fibre xylan. According to the present belief, the xylanases act mainly on the xylan located on the surface of the pulp fibres (Kantelinen et al 1991). Hemicellulase (xylanase) treatments have been combined with various bleaching sequences. The use of enzymes in bleaching has been evaluated by peroxide delignification (Viikari et al. 1986, Viikari et al. 1987, Viikari et al. 1990) and by various chlorine bleaching sequences carried out .on laboratory scale. Industrially enzyme treatments have been combined with different chlorine bleaching sequences and also with various multistage peroxide bleaching sequences (Viikari et al. 1991b). However, ev
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Buchert Johanna
Penttila Merja
Ranua Marjatta
Saloheimo Anu
Siika-aho Matti
Alko Ltd.
Hobbs Lisa J.
Wax Robert A.
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