An ultrastructural search for lectin-binding sites on surfaces of spinach leaf organelles |
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Authors: | Sue Ellen Frederick Barbara Nies Peter J Gruber |
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Institution: | (1) Department of Biological Sciences, Mount Holyoke College, 01075 South Hadley, MA, USA |
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Abstract: | Organelles isolated from leaves of spinach (Spinacia oleracea L.) were prefixed in glutaraldehyde and then incubated with ferritin conjugates of four lectins — Concanavalin A (Con A), Ricinus communis L. agglutinin, MW 120,000 (RCA), soybean agglutinin (SBA), and wheat germ agglutinin (WGA) — in order to probe their cytoplasmic surfaces for saccharide residues. In each case the major leaf organelles, including microbodies, mitochondria and chloroplast derivatives, failed to exhibit labeling when examined with the electron microscope. Tobacco (Nicotiana tabacum L.) leaf protoplasts, incubated simultaneously with and under identical conditions to the spinach organelles, showed specific labeling of their plasma membranes with all four lectin conjugates, thus establishing the efficacy of the procedure for demonstrating the presence of binding sites when they exist. Further attempts to show binding of one of the lectins, Con A, by labeling with fluorescein-Con A and by organelle agglutination, yielded results consistent with the absence of ultrastructural labeling. It is concluded that no saccharide residues recognized by the four lectins are present on the cytoplasmic surfaces of organelles and that those residues reported to be constituents of intracellular membranes, therefore, are most likely exposed on the luminal (extracytoplasmic) surfaces.Abbreviations Con A
Concanavalin A
- RCA
Ricinus communis agglutinin, MW 120,000
- SBA
soybean agglutinin
- WGA
wheat germ agglutinin |
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Keywords: | Lectin binding Membranes (surfaces) Nicotiana Organelles (leaf) Protoplasts Spinacia |
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