A rapid method for the assay of dextranase

Molecular basis of auxin-regulated extension growth and role of dextranase

The first step in the extension growth of the plant cell is a process in which the cell wall becomes ductile or plastic, after which the actual enlargement takes place passively under the influence of turgor. The nature of this process has not been explained, although much research has been carried out concerning it. In the present report, it is shown that a specific enzyme, which is identical or nearly so with dextranase (alpha-1,6-D-glucan 6-glucanohydrolase, EC 3.2.1.11) and is associated with the cell walls of growing coleoptiles, plays a prominent role in this process. The action of this enzyme is dependent on the level of growth hormone, auxin, in the tissue. Under its action, certain cell wall components are broken down to yield arabinose and glucose. These sugars are also released during autolysis of cell wall material. The molecular linkages broken in the process are probably the arabinogalactan crosslinks of the hemicellulose matrix, which are the main constituents of the wall containing arabinose. This is substantiated by the finding that dextranase can break down arabinan and compounds containing arabinose chains with the release of arabinose, just as in the action of the enzyme on the wall. The breaking of these crosslinks will impart the necessary plasticity to the wall for cell extension to occur.

Microbial dextran-hydrolyzing enzymes: fundamentals and applications

Dextran is a chemically and physically complex polymer, breakdown of which is carried out by a variety of endo- and exodextranases. Enzymes in many groups can be classified as dextranases according to function: such enzymes include dextranhydrolases, glucodextranases, exoisomaltohydrolases, exoisomaltotriohydrases, and branched-dextran exo-1,2-alpha-glucosidases. Cycloisomalto-oligosaccharide glucanotransferase does not formally belong to the dextranases even though its side reaction produces hydrolyzed dextrans. A new classification system for glycosylhydrolases and glycosyltransferases, which is based on amino acid sequence similarities, divides the dextranases into five families. However, this classification is still incomplete since sequence information is missing for many of the enzymes that have been biochemically characterized as dextranases. Dextran-degrading enzymes have been isolated from a wide range of microorganisms. The major characteristics of these enzymes, the methods for analyzing their activities and biological roles, analysis of primary sequence data, and three-dimensional structures of dextranases have been dealt with in this review. Dextranases are promising for future use in various scientific and biotechnological applications.

The cell surface of Trypanosoma musculi bloodstream forms. II. Lectin and immunologic studies

Living Trypanosoma musculi bloodstream trypomastigotes were agglutinated specifically with concanavalin A (ConA), wheat germ agglutinin (WGA), soybean agglutinin (SBA), and fucose-binding protein (FBP). The agglutination with these lectins of living cells from which the coat was removed by trypsinization was the same as with intact trypanosomes. Glutaraldehyde or formalin fixation did not affect the results with regard to agglutination with WGA, SBA, and FBP, but lower agglutination with ConA was observed upon fixation. By using a dense iron-dextran marker many fewer ConA marker particles were localized at the fine structural level in the intact than in trypsin-treated trypanosomes. On the basis of the results obtained by agglutination and electron microscopy, it is likely that fixation cross-links intact surface-coat components associated with the ConA binding sites. It is evident from the studies in which lectins were employed that ligands containing alpha-D-mannose, N-acetylglucosamine, N-acetylgalactosamine, and alpha-L-fucose are randomly distributed in the outer surface of the pellicular and flagellar membranes of T. musculi trypomastigotes. Results obtained with alpha-amylase- and dextranase-treated trypanosomes suggested that lectin-binding sugar ligands in the cell surface were not directly associated with alpha-1,4 or repetitive alpha-1,6 glucan-bonded polysaccharide moieties. Similar conclusions can be drawn on the basis of neuraminidase treatment with regard to N-acetylated neuraminic acids. After thorough washing, intact, but not trypsin-treated trypomastigotes were agglutinated specifically with antisera against whole mouse serum and against mouse IgG. Evidently, adsorbed constituents of mouse serum are regular components of the T. musculi surface coat. After incubation in dilute whole mouse serum or in mouse IgG solutions, also the trypsinized cells were agglutinated by the 2 antisera. No such results were obtained with trypsinized cells incubated in serum-free buffers. It was concluded that mouse serum proteins were readily readsorbed on, and firmly bound to the trypsinized cells' surfaces. Specific agglutinations were obtained with trypsinized cells after incubation in dilute rat, rabbit, bovine, and human sera and in solutions of rat and rabbit IgG in reactions with the corresponding antisera. It seems, therefore, that the host serum proteins are adsorbed nonspecifically to the cell surface of trypsinized T. musculi bloodstream forms. When examined by electron microscopy, the intact trypomastigotes were covered by an ununiform, slightly granular, fibrillar extracellular coat, applied to the entire outer lamina of the pellicular and flagellar membranes. No indication of such a coat was noted in the trypsinized organisms. Flocculent surface coat-like matrix could, however, be discerned in cells which, after trypsinization, were incubated in various sera.