Cellulase assay methods: a review

Cellulase activity of Leishmania major in the sandfly vector and in culture

The secretion of cellulose-degrading enzymes by Leishmania promastigotes in culture and in the sandfly vector was demonstrated. Two types of activity of cellulase enzyme-complexes were measured: endoglucanases, which randomly cleave cellulose chains and cellobioydrolases, which remove cellobiose from the nonreducing end of the molecule. The assays demonstrated that enzymes with these activities were secreted into the culture medium by Leishmania major, L. donovani, and L. braziliensis. These activities were also found in cultures of Sauroleishmania agamae, Leptomonas seymouri, Herpetomonas muscarum, Crithidia fasciculata and Trypanosoma brucei brucei that had a relatively low endoglucanase activity. Both endoglucanase and cellobiohydrolase activities were found in the gut of L. major-infected Phlebotomus papatasi, while gut preparations of uninfected sandflies had only cellobiohydrolase activity. The similar growth of L. major parasites in medium supplemented with either cellulose or glucose suggests these parasites can utilize cellulose.

Cloning, expression in Escherichia coli, and characterization of cellulolytic enzymes of Azoarcus sp., a root-invading diazotroph

We screened members of a new genus of grass-associated diazotrophs (Azoarcus spp.) for the presence of cellulolytic enzymes. Out of five Azoarcus strains representing different species, only in the endorhizosphere isolate BH72, which is also capable of invading grass roots, was significant endoglucanase activity, in addition to beta-glucosidase and cellobiohydrolase activity, present. Reducing sugars were readily released from medium-viscosity carboxymethylcellulose (CMC), but neither CMC, cellulose filter strips, Avicel, cellobiose, nor D-glucose served as the sole carbon source for growth of Azoarcus spp. Clones from a plasmid library of strain BH72 expressed all three enzymes in Escherichia coli, apparently not from their own promoter. According to restriction endonuclease mapping and subclone analysis, beta-glucosidase and cellobiohydrolase activities were localized on a single 2.6-kb fragment not physically linked to a 1.45-kb fragment from which endoglucanase (egl) was expressed. Two isoenzymes of endoglucanase probably resulting from proteolytic cleavage had pI values of 6.4 and 6.1 and an apparent molecular mass of approximately 36 kDa. Cellobiohydrolase and beta-glucosidase activity were conferred by one enzyme 41 kDa in size with a pI of 5.4, which we classified as an unspecific exoglycanase (exg) according to substrate utilization and specificity mapping; hydrolysis of various oligomeric substrates differentiated it from endoglucanase, which degraded substituted soluble cellulose derivatives but not microcrystalline cellulose. Both enzymes were not excreted but were associated with the surface of Azoarcus cells. Both activities were only slightly influenced by the presence of CMC or D-glucose in the growth medium but were enhanced by ethanol. egl was located on a large transcript approximately 15 kb in size, which was detectable only in cells grown under microaerobic conditions on N2. Surface-bound exo- and endoglucanases with some unusual regulatory features, detected in this study in a strain which is unable to metabolize cellulose or sugars, might assist Azoarcus sp. strain BH72 in infection of grass roots.

Purification and properties of a beta-1,4-xylanase from a cellulolytic extreme thermophile expressed in Escherichia coli

1. An endoxylanase (EC 3.2.1.8) was purified from an Escherichia coli strain carrying a xylanase gene from the extreme thermophile "Caldocellum saccharolyticum" strain Tp8T6.3.3.1. It was found to have an M(r) of 42,000 and an isoelectric point of approx. 5.0. 2. The enzyme showed optimum activity at pH 5.0-7.7 and had an activation energy of 44 kJ mol-1. It was stable at room temperature at pH 4.5-11.5 in the presence of 0.5 mg ml-1 bovine serum albumin. The half-life of the enzyme at 75 degrees C was 20 min at pH 6.0 in the presence of 0.5 mg ml-1 bovine serum albumin. 3. The xylanase had highest activity on oat spelts xylan, releasing xylobiose and some xylotriose. The Km for oat spelts xylan was 0.021% (w/v) at pH 6.0. 4. The enzyme had high activity on sugar cane bagasse hemicelluloses A and B, lower activity on larchwood xylan and also hydrolysed carboxymethylcellulose, 4-methylumbelliferyl beta-D-cellobioside and p-nitrophenyl beta-D-cellobioside, but could not hydrolyse xylobiose. 5. It showed transferase activity on p-nitrophenyl beta-D-xylopyranoside. Xylose did not inhibit the enzyme.

Black substrate for spectrophotometric determination of cellulase activity in coloured solutions

A simple procedure for spectrophotometric determination of cellulase activity in coloured solutions is described. CM-cellulose, cross-linked with epichlorhydrin in the presence of black drawing ink, is used as an insoluble chromolytic substrate. The absorbance of reaction mixture filtrates are read in the near infra-red region (at 800-900 nm) where the absorbances of contaminating coloured substances are substantially lowered; by contrast, black drawing ink released from the substrate during the action of cellulases absorbs strongly at these wavelengths.

Estimation of cellulase activity using a glucose-oxidase-Cu(II) reducing assay for glucose

In the presence of the Cu(I)-chelating agent neocuproine (2,10-dimethyl-1,9-phenanthroline) hydrogen peroxide acts as a reductant of Cu(II). The reaction does not proceed in the absence of neocuproine and the addition of EDTA to the reaction mixture prior to addition of Cu(II) also inhibits the reduction. Colour development can be arrested and stabilized by addition of EDTA. The reaction can be used to estimate hydrogen peroxide concentrations in the range 0.68-6.8 micrograms/ml and glucose concentrations in the range 3.6-36 micrograms/ml (20-200 microM). Horseradish peroxidase is not required for the peroxide assay but glucose oxidase must be used for glucose estimations. Thermostable cellulase activity has been estimated at 60 degrees C against cellobiose, carboxymethylcellulose and cellulose substrates by estimation of the glucose released from the substrates.