Immuno-scanning electron microscopic localization of extracellular polysaccharidases within the fibrillar sheath of the brown rot fungus Postia placenta
F Green III, C A Clausen, M J Larsen, T L Highley
Extracellular polysaccharidases of the brown-rot fungus Postia placenta were localized using colloidal gold labeled monoclonal antibodies to the B-1,4-xylanase (32-36kDa) fraction of Postia placenta. Postia placenta was grown from agar onto glass coverslips, immunolabeled with or without prior fixation, and examined by SEM. Enzymes were localized on the hyphal surface and on the clumped fibrillar elements (mycofibrils) of the hyphal sheath following fixation with enzymes. If fixation was omitted, labeling was diffuse and not localized on individual or clumped mycofibrils. We conclude that extracellular decay enzymes are weakly bound (non-covalently), but not identical to, the linear mycofibrillar elements of the hyphal sheath. Enzymes appear to dissociate into the water soluble glucan matrix of the sheath during incubation in physiological buffers when fixation is omitted.