Purification and Properties of a Thermo-labile Antigen from Bakers Yeast Cells

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A thermo-labile antigen (TLA) on the yeast cell surface was isolated from a yeast cell autolyzate and purified to a homogeneous state by chromatography on an immunoadsorbent affinity column. The molecular weight of TLA was about 1.45 x 105 on SDS-polyacrylamide gel electrophoresis and about 1.5x 105 on gel chromatography on Sephadex G-200. The TLA contained 74.5% protein and 25.5% sugar. It was characterized by high contents of glycine, glutamic acid, serine and aspartic acid. Half-cystine, methionine, histidine and arginine were not found. The sugar moiety was composed of galactose, mannose, 7V-acetylglucosamine and fucose. The antigenic determinant of TLAwas distinct from that of cell wall mannan in the Ouchterlony immunodiffusion test. No precipitin line against anti-TLA serum was observed, when TLAwas heated at 90°C for 10 min. Oxidation with periodate had little effect on antigenicity, but digestion with Pronase or treatment with protein denaturants resulted in loss of the antigenicity. These results suggest that the protein moiety plays an important role as the antigenic determinant of TLA. Moreover, the antiserum specific to TLAagglutinated fresh yeast cells, and the distribution ofTLA was apparent on the yeast cell surface by immunofluorescence staining. These findings suggest that TLAmolecules were exposed on the outer surface of the yeast cell wall.
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