Xylanases molecular weight

The only major accessory enzyme purified thus far for the xylanase was an a-(l,3)-L-arabinosidase with a molecular weight of 66,(XX) and isoelectric point of 4.1 (publication in preparation). The enzyme was not capable of acting on intact xylans. However, it acted on the end-products of arabinoxylan (but not glucuronoxylan) degradation by the xylanase, doubling the total extent of degradation. 

Elimination of Cellulases from Xylanases. Classical methods of protein fractionation can be used for to separate cellulases and xylanases on a large scale only when they differ considerably in molecular weight or isoelectric point. The Tricho-derma harzianum enzymes were separated by ultrafiltration because the xylanase was smaller and passed through the membrane into the ultrafiltrate 18). Fractional precipitation with organic solvents is another possibility (7). 

Low-Molecular Weight Xylanase Inducers. The response of cellulolytic fungi to low-molecular weight fragments of xylan and ceUulose confirmed the separate regulatory control of the formation of xylanases and ceUulases. Xylobiose [Xylp-p-(l- 4)-Xylp] was a specific inducer of xylanases in T. reesei (61) and Aspergillus terreus (67). Sophorose and otho glucobioses selectively induced the synthesis of... 

The variety of control mechanisms of xylanase synthesis is demonstrated by examples of the synthesis of xylanase induced by xylose (38,74,75). To a list of low-molecular weight xylanase inducers one can add 4-thioxylobiose (80,81) and 4-O-p-D-xylopyranosyl-L-arabinopyranose (73,77). 

Attempted purifications of Xylanase I, which has an apparent molecular weight four to six times that of Xylanase II by gel permeation chromatography, by various chromatographic procedures all failed, as more Xylanase II continued to form as the solution underwent dilution (Pestlin, S., Iowa State University, unpublished data). Xylanase I therefore appeared to be cluster of Xylanase II molecules. 

Feruloyl esterase activity was first detected in culture filtrates of Strepto-myces olivochromogenes (49), and has thereafter also been reported for some hemicellulolytic fungi (Table III). A partially purified feruloyl esterase from S. commune liberated hardly any ferulic acid without the presence of xylanase (65). Very recently a feruloyl esterase was purified from Aspergillus oryzae (Tenkanen, M. Schuseil, J. Puls, J. Poutanen, K., /. Biotechnol, in press). The enzyme is an acidic monomeric protein having an isoelectric point of 3.6 and a molecular weight of 30 kDa. It has wide substrate specificity, liberating ferulic, p-coumaric, and acetic acids from steam-extracted wheat straw arabinoxylan. 

There are many recent examples of xylanase induction in fungi grown on media containing xylan, hemicellulose-rich material and low molecular weight carbohydrates (42-66). It has generally been observed that higher... 

The combined action of xylanase and mannanase on sprucewood holocellulose increased the hydrolysis of hemicelluloses without any detectable attack of cellulose. At the end of the experiments—i.e., after 48 hr of xylanase incubation followed by 32 hr of combined xylanase-mannanase incubation—about half the hemicelluloses present in the starting material were selectively converted into low-molecular-weight sugars. The amount of mannan removed was two times higher than after 80 hr of incubation with mannanase only. Unexpectedly, the xylan dissolution was scarcely increased by the combined action of the two hemicellulases. 

Several amylases have been partially sequenced (42-45). For example, a-amylase from Bacillus subtilis, which is composed of two subunits of 24,000 molecular weight each, has an amino terminal sequence as shown in Table V (42). Perhaps fortuitously, the sequence of residues 8 through 12 resembles residues 14 through 18 in xylanase A, in that a polar residue is surrounded by four aromatic residues. 

The molecular weights of D-xylanase preparations of different origins (see Table XXII), like those of the other hemicellulases (see Sections II, III, and IV), are relatively low, ranging from 16,000 to 38,000. The pi values reported for several D-xylanases are also shown in Table XXII, and, with the exception of the Ceratocystis paradoxa D-xylanase I (Ref. 228) (pi 9.17), are mainly acid gly-canases. 

Molecular Weight, Isoelectric Point, and Km Values of D-Xylanases of Different Fungal Origin... 

Bedford, M. R., Classen, H. L. (1992). The influence of dietary xylanase on intestinal viscosity and molecular weight distribution of carbohydrates in rye-fed broiler chick. In J. Visser, G. Beldman, M. A. Kusters-Van Someren, A. G. J. Voragen (Eds.) Xylans and xylanases (pp. 361-370). Amsterdam Elsevier. 

Enzyme preparations active against crystalline cellulose, marble-milled filter paper, carboxymethylcellulose (CM-cellulose), hemicellulose, and D-xylan have been obtained from cultures of Ruminococcus flavefaciens. Carboxymethyl cellulase and D-xylanase activities were present in a high molecular weight complex (see p. 461). 

Enzymes are used also in fruit juice manufacturing. Addition of pectinase, xylanase, and ceUulase improve the liberation of the juice from the pulp. Pectinases and amylases are used in juice clarification. Similarly enzymes are widely used in wine production to obtain a better extraction of the necessary components, and thus improving the yield. Enzymes hydrolyze the high molecular weight substances like pectin. 

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