Chemistry and Architecture of the Mycelial Wall of Agaricus bisporus

Abstract

SUMMARY: A purified wall fraction was prepared from the mycelium of Agaricus bisporus. The isolated wall consisted of 43% (w/w) chitin, 14% KOH-soluble glucan, 27% β-glucan, 16% protein and 1·5% lipid. Traces of mannose and xylose were detected by gas chromatography. The architecture of the wall was investigated with sequential enzyme digestion and electron microscopy. The outer wall surface is covered by a mucilage that is removed by the isolation procedure. The wall fraction could be completely degraded by extraction in warm I m-KOH followed by digestion with a mixed β-glucanase and then chitinase. The outer layer of KOH-soluble glucan is amorphous and of variable thickness. Incubation with glucanase did not change the dimensions of the wall but was necessary before the inner wall was susceptible to attack by chitinase, indicating that β-glucan does not constitute a separate wall layer but is a matrix associated with the fibrillar chitin. The inner layer presents an even, compact, fibrillar side as the inside surface of the wall, but is looser and uneven outwardly where it interdigitates with the irregular inner surface of the KOH-soluble glucan. Silver hexamide staining showed cystine-containing protein throughout the wall.