Soluble Factors in Pisum Extracts Which Moderate Pisum β-Glucan Synthetase Activity

Abstract

(14,17) that at least part of total fl-glucan synthetase activity is subject to rapid turnover in vivo.The aims of the present study were, in part, to assess the potential of the pea extract components to act as synthetasemoderating regulators in vivo. The intent was also to examine their properties, bearing in mind that it might be possible to exploit a natural activator and minimize effects of any destructive agent during tissue homogenization in order to prepare a more effective ,8-glucan synthetase complex for studies in vitro.Brief reports have appeared indicating that crude extracts from pea epicotyl (12,13,20) and lupin hypocotyl (21) contain a heatlabile component which suppresses membrane-bound 81-glucan synthetase activity, and a heat-stable component which enhances it. Little is known of the specificities or modes of action of these factors beyond the observations that they have different effects on the products synthesized from UDP-glucose and GDP-glucose (13), implying specificity, and the labile component appears to act with a pH optimum close to 7 (20). It is possible that these components represent natural regulators of cellulose or callose synthesis in a manner analogous to the role postulated for specific proteases in controlling fungal chitin (3, 9) and f8-1,3-glucan (23) synthetase activities, as well as turnover of numerous other plant enzymes. It is also possible that the net deleterious effect of crude extracts on synthetase activity, which is particularly evident when assays are conducted with tissue slices (13), i.e. cell surface synthetase (15, 18), is responsible in part for the difficulties encountered in achieving rates of f,-glucan synthesis by isolated particulate fractions comparable to those observed in vivo (7,13,15,18 MATERIALS AND METHODSThe source of growing tissue used throughout this study is the apical 10 mm, defined here as a "segment" (about 25 mg fresh wt), cut from the third internode of pea epicotyls. Seedlings were grown as described earlier (15,18). Methods for assaying fB-glucan synthetase activity in this tissue are based on previous results (17,18,20) and basic information on optimal conditions (15

Intermediatry steps in Acetobacter xylinum cellulose synthesis: studies with whole cells and cell-free preparations of the wild type and a celluloseless mutant

“…The low specific activity of the cell-free system, which is about 0.2% of cellulose synthesis from glucose by whole cells, and the progressive loss of activity of these particulate preparations could be related to their lack of a specific acceptor or some structural factor of the cell wall or membrane and reflect the dependence of effective cellulose synthesis on the physical integrity of essential enzymatic and structural components of the synthetic system (3,11,16). Such a deficiency of the particulate preparation could also explain why more glucose of UDP-glucose was incorporated into the glucoprotein than in the presumed final product, the ,B-1,4-glucan ( Fig.…”

Pea Xyloglucan and Cellulose

“…The activities of both buffer-soluble and -insoluble endo-1,4-0-glucanases (Table II) increased markedly only in 2,4-1-treated tissue (13). Since pea xyloglucan is highly susceptible to hydrolysis by these enzymes (8, 11), their activity fl-Glucan synthase activity, assayed under conditions where [1][2][3][4] linkages predominate in the products (4,15,18), increased in the tissue only after 2,4-D treatment (Table II). When assayed in pea membranes under conditions where 1-3 linkages predominate, synthase activity increased in the tissue during elongation growth or after treatment with auxin, but decreased after treatment with ethylene (Table II).…”